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Publisher: Elsevier   (Total: 3184 journals)

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Showing 1 - 200 of 3184 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 37, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 25, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 100, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 27, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 37, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 5)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 432, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 28, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 3)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 10, SJR: 0.18, CiteScore: 1)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 295, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 6, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 26, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 7, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 17, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 9, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 11, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 182, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 16, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 29, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 11, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 15, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 32, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 5)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 14)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 28, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 13)
Advances in Digestive Medicine     Open Access   (Followers: 12)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 26)
Advances in Ecological Research     Full-text available via subscription   (Followers: 43, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 49, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 62, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 20, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 10, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 24, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 12, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 23)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 3, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 20, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 12, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 7, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 23)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 17, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 25, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 17)
Advances in Pharmacology     Full-text available via subscription   (Followers: 16, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 10)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 65)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 1, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 416, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 13, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 36, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 20)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 51, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 368, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 11, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 471, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 17, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 44, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 58, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 6, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 11)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 2, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 10, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 53, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 5, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 5, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 6)
American Heart J.     Hybrid Journal   (Followers: 57, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 62, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 45, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 11)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 13, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 34, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 29, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 35, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 49)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 239, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 30, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 39, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 64, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 21, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 44, SJR: 1.512, CiteScore: 5)
Analytica Chimica Acta : X     Open Access  
Analytical Biochemistry     Hybrid Journal   (Followers: 204, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 12, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 14)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 25, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 210, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 6, SJR: 0.937, CiteScore: 2)
Animal Reproduction Science     Hybrid Journal   (Followers: 7, SJR: 0.704, CiteScore: 2)

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Similar Journals
Journal Cover
Natural Gas Industry B
Number of Followers: 0  

  This is an Open Access Journal Open Access journal
ISSN (Print) 2352-8540
Published by Elsevier Homepage  [3184 journals]
  • Decomposition characteristics of natural gas hydrates in hydraulic lifting
           pipelines

    • Abstract: Publication date: Available online 20 March 2019Source: Natural Gas Industry BAuthor(s): Hailiang Xu, Weiyang Kong, Fangqiong Yang For the sake of guiding parameter setting of the hydraulic lifting pipeline system for cutter-suction mining of natural gas hydrates (“hydrates” for short) on the seabed, the decomposition characteristics of hydrates in hydraulic lifting pipelines and the effects of flow parameters on decomposition characteristics were studied in this paper. A temperature–pressure model for the hydrate hydraulic lifting pipeline, a hydrate decomposition mass transfer model and a pipeline multiphase flow model were established using mathematical modeling method according to thermodynamics and fluid mechanics. Then, the relationships of the temperature and pressure of pipeline fluid, the amount of hydrate particulate matter and the decomposition surface vs. the underwater depth under the effect of different influencing factors during the transformation from solid–liquid two-phase flow to solid–liquid–gas three-phase flow were analyzed. And the following research results were obtained. First, the decomposition of hydrate slows down and the decomposition surface moves upward slightly with the increase of flow rate in the pipeline. Second, particle size basically has no effects on the temperature and pressure of pipeline fluid, the hydrate phase equilibrium pressure and hydrate decomposition surface. However, only the hydrate particles whose diameter is smaller than 0.2 mm can be completely decomposed in the pipeline while the decomposition of those whose particles size is greater than 2.0 mm is negligible. Third, if the back pressure at the outlet is positive, the decomposition surface moves upward and the decomposition of hydrate slows down with the increase of the back pressure. And if the back pressure at the outlet is negative, the decomposition surface moves downward and the decomposition of hydrate speeds up with the increase of the back pressure. Fourth, the decomposition of hydrate slows down and the decomposition surface moves upward with the increase of mineral depth. However, the decomposition rate and decomposition surface are basically unchanged when the mineral depth is below 1500 m under water. Fifth, the experimental results are basically consistent with the numerical simulation results, and it is indicated that the newly established models are of high reliability. In conclusion, decomposition surface height and decomposition rate can be adjusted by controlling flow rate and outlet back pressure rationally during the cutter-suction mining of hydrates while the influences of particle diameter and mining depth on gas production need not be taken into consideration.
       
  • Application of the loop method to the preparation of gas reference
           material

    • Abstract: Publication date: Available online 19 March 2019Source: Natural Gas Industry BAuthor(s): Zheng Fang, Xin Zhou, Zhi'ang Li, Fanfeng Deng, Liaoyu Dong, Liwen Zheng High-accuracy gas reference material is an important prerequisite to guaranteeing the accuracy of stoichiometry. At present, however, the existing procedures of preparing gas reference material are complicated and time-consuming with high degree of uncertainty, so it is difficult to realize the high-accuracy measurement of gas compositions. In this paper, a loop method of preparing the gas reference material was developed. Then, its uncertainty degree on trace materials and preparation process was assessed and compared with the preparation process of the traditional dilution method. Finally, its weighing value was verified by means of a gas chromatography. And the following research results were obtained. First, the weighing cylinder of traditional preparation methods need a balance of wide range and low precision, so the uncertainty degree in the weighing process is introduced many times by multi-stage dilution. Second, when the loop method is adopted to prepare mixed gas reference material, the preparation can be completed in one step, so the uncertainty degree introduced in the preparation process is decreased by one order of magnitude. Third, by virtue of the loop method, the previously-used preparation procedures are simplified, the consumption of raw material is reduced and the preparation efficiency of mixed gas reference material is increased. Fourth, the loop method has been successfully applied to the preparation of gas reference material of natural gas and sulfide mixtures, and it is promising in more extensive application to realize efficient preparation and accurate valuing of gas reference material. And fifth, a gas chromatography is used to verify the nominal value of mixed gas reference material prepared by the loop method. And it is indicated that the loop method is of strong feasibility and accuracy.
       
  • Application of CBM horizontal well development technology in the roof
           strata close to broken-soft coal seams

    • Abstract: Publication date: Available online 16 March 2019Source: Natural Gas Industry BAuthor(s): Yaobo Xu, Yushuang Zhu, Peihe Zhang Broken coal structure and low permeability are the main reasons for the difficult production of coalbed methane (CBM) in broken-soft coal seams. In this paper, No.8 coal seam in the Luling Mine of the Huaibei Coal Field was taken as an example to study the way to improve CBM production of broken-soft coal reservoirs. First, drilling, fracturing and production of horizontal wells were considered comprehensively. Then, based on the idea of exploiting CBM through horizontal wells in roof strata close to the broken-soft coal seams, the propagation laws of fractures created by layer-penetrating fracturing of horizontal wells in roof strata were studied, and accordingly the location of horizontal well was optimized. Finally, the CBM horizontal well exploitation technology for the roof strata close to coal seams was developed and tested on site. And the following research results were obtained. First, the vertical fractures created during layer-penetrating fracturing of horizontal wells in roof strata can propagate from the roof strata with high stress values downward to the coal seam with low stress values. In addition, the location of horizontal well has an important influence on the effect of layer-penetrating fracturing. The closer the horizontal well is to the coal seam, the better the fracture propagation effect of layer-penetrating fracturing. Second, the horizontal well should be arranged in the roof strata 1.5 m away from the top of coal seam, so that fracturing stimulation requirements of horizontal wells in roof strata can be satisfied to the uttermost. Third, three key technologies are formed, including the “high-quality, fast and safe” drilling technology, the deep-penetration oriented perforating technology and the “large displacement, large scale, high pad ratio and moderate proppant concentration” active water fracturing technology. Fourth, the gas production with this technology in engineering practice is remarkable. In conclusion, the CBM development technology of horizontal wells in roof strata close to broken-soft coal seams is feasible. The research results provide a new technical method for the development of CBM in broken-soft coal seams.
       
  • Calculation and analysis of dynamic drag and torque of horizontal well
           strings

    • Abstract: Publication date: Available online 16 March 2019Source: Natural Gas Industry BAuthor(s): Xiaohua Zhu, Ke Li, Jiawei An In recent years, shale gas production horizontal well types mainly include conventional horizontal well, highly deviated well and scoop-shape horizontal well. For the sake of construction decision making, it is necessary to study these three types of wells from the aspects of drag and torque characteristic, weight on bit transferring efficiency, key hole sections or links and extreme penetration length. In this paper, these three types of horizontal wells were taken as the study objects. Their drag and torque, load transfer and extended reach drilling were explored based on the dynamic model of full hole drilling string and the simulation calculation of dynamic characteristics of full hole drilling string system. And the results were applied and tested on site in three shale gas wells (a conventional horizontal well, a highly deviated well and a scoop-shape horizontal well) in the Changning area, Sichuan Basin. And the following research results were obtained. First, the contact friction strength of the deeper part of the buildup section in the scoop-shape horizontal well is very high, and it is 1.67 times that of the hold section. The total contact force of buildup section in the scoop-shape horizontal well is 1.62 times that in the highly deviated well. Second, the contact friction strength of the hold section in highly deviated well is not only higher than that of its buildup section, but also higher than any characteristic section in the three well types of the same depth. Third, the operating stress of drilling strings during the drilling of three well types is not high, but during the extended reach drilling in the curved section of the scoop-shape horizontal well, it is necessary to focus on the twist off of drilling string in the hold section. Fourth, the weight on bit transferring efficiency of scoop-shape horizontal well is lower than that of conventional horizontal well and highly deviated well. In conclusion, the research results preliminarily reveal the drag and torque characteristics and active load transferring mechanisms of conventional horizontal well, highly deviated well and scoop-shape horizontal well for shale gas production, and present important hole sections for safety assessment. They can be used as references for efficient and safe construction of shale gas horizontal wells.
       
  • A new quantitative evaluation method for development area selection of
           tight gas and CBM commingled production

    • Abstract: Publication date: Available online 16 March 2019Source: Natural Gas Industry BAuthor(s): Yuhu Bai Existing evaluation methods used for the development area selection for commingled production of tight gas and coalbed methane (CBM) are poorly universal and their parameters (e.g. reserves and reservoir physical properties) cannot reflect the production rate difference during commingled production of tight gas and CBM. In this paper, an integrated evaluation coefficient used for evaluating favorable commingled production areas of tight gas and CBM was defined so as to establish a universal quantitative evaluation index system. Then, by means of orthogonal design together with numerical simulation, the key parameters influencing the commingled production rate and their influence degree on the production rate were determined by taking the commingled production rate as the evaluation target. Finally, a new quantitative evaluation method for the development area selection for commingled production of tight gas and CBM was established. And the following research results were obtained. First, by virtue of the new quantitative evaluation method, the geological occurrence model of tight gas and CBM, the key evaluation parameter and the orthogonal experiment design are established, and the influence degree of evaluation parameters on production rate and the integrated evaluation coefficient of favorable commingled production area of tight gas and CBM are determined. Second, the quantitative evaluation results on the development areas of commingled production of tight gas and CBM in KNW Block based on 12 selected key parameters show that the southern KNW Block and the Well block KNW-37 in the north of KNW Block are the favorable areas for single production of tight gas, Well blocks KNW-10, KNW-33 and KNW-9 are the favorable areas for single production of CBM, and the central and southwestern areas are the favorable areas for the commingled production of tight gas and CBM. In conclusion, this new quantitative evaluation method is universal and can be used as reference for the development area selection for commingled production of tight gas and CBM.
       
  • Stress corrosion cracking behavior of X90 pipeline steel and its weld
           joint at different applied potentials in near-neutral solutions

    • Abstract: Publication date: Available online 16 March 2019Source: Natural Gas Industry BAuthor(s): Jinheng Luo, Sheji Luo, Lifeng Li, Liang Zhang, Gang Wu, Lixia Zhu X90 pipeline steel is a new generation of pipeline steel developed after X80 and X100 pipeline steels, and it is now a new research hotspot at home. In order to thoroughly study the effect of applied potential on the soil stress corrosion cracking (SCC) behavior of X90 pipeline steel, we investigated the SCC behaviors of base metal and weld joint samples in the straight-weld pipe of X90 pipeline steel at different applied potentials in near-neutral solution using electrochemical measurements methods and slow strain rate testing (SSRT). Besides, the fracture surfaces were observed through scanning electron microscope (SEM) and the mechanisms of the corrosion cracking behaviors were analyzed. And the following research results were obtained. First, the polarization curves of the base metal and weld joint samples in the NS4 solution present the typical characteristics of anodic dissolution but no activation–passivation phenomenon happens. Second, in the NS4 solution, the base metal and weld joint samples present SCC sensitivity. The SCC sensitivity indicator which is expressed by yield loss percentage elongation and yield loss percentage elongation area decreases firstly and then increases with the negative increase of the applied potential, and the SCC sensitivity of weld joint is higher than that of base metal. Third, there are three mechanisms on the SCC behaviors of base metal and weld joint samples, i.e., anodic dissolution mechanism when the applied potential is open circuit potential (EOCP), anodic dissolution and hydrogen embrittlement mechanism when the applied potential is −850 mV, and hydrogen embrittlement mechanism when the applied potential is −1000 mV and −1200 mV. It is concluded that the research results can provide a technical support and theoretical basis for the large-scale application of X90 pipeline steel.
       
  • Damage mechanism of cement slurry to CBM reservoirs with developed
           fractures and cleats: A case study from eastern Yunnan and western Guizhou
           in China

    • Abstract: Publication date: Available online 16 March 2019Source: Natural Gas Industry BAuthor(s): Hansen Sun, Chengwen Wang The coalbed methane (CBM) reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures, so cementing slurry (“slurry” for short) can invade into CBM reservoir easily, resulting in reservoir damage and abnormal increase of reservoir transformation fracturing pressure. In order to reveal the damage mechanisms of slurry to this type of coal reservoirs, we analyzed the physical and chemical properties and potential damage modes of coal rocks. Then, the development situations of fractures and pores before and after the coal core samples were internally contaminated and the invasion and plugging situations of slurry in fractures and pores were analyzed intuitively by means of CT scanning and scanning electron microscope (SEM), and the percentage of slurry and fractures in coal core volume was calculated. In this way, a method to quantitatively evaluate the damage of slurry to coal reservoirs was established. And the following research results were obtained. First, under the effect of differential pressure, slurry and its filtrate invade into coal reservoirs along the fractures. The invasion degree varies with the development degree of fractures and pores. The more developed the fractures and pores, the higher the invasion degree. Second, the cement products formed after the slurry in the reservoirs gets cemented and solidified fill the fractures and pores tightly and cover the surface of coal core samples densely, so CBM flowing channels are blocked severely. Consequently, the permeability of coal core samples decreases and the compressive strength of coal rocks increase, leading to the abnormal increase of subsequent fracturing pressure and impacting the fracturing stimulation effects. Third, the effect of slurry filtrate on the alkali sensitivity and velocity sensitivity of coal rocks is much less than the damage degree of slurry invasion to coal rocks. In conclusion, this newly developed quantitative evaluation method for the damage of slurry to coal reservoirs is of guiding significance to improving the cement job quality of coal reservoirs and ensuring the efficient CBM development.
       
  • Laboratory experiments on blockage removing and stimulation of CBM
           reservoirs by composite pulsating hydraulic fracturing of radial
           horizontal wells

    • Abstract: Publication date: Available online 16 March 2019Source: Natural Gas Industry BAuthor(s): Shouceng Tian, Zhongwei Huang, Gensheng Li, Peiqing Lu, Hongyuan Zhang, Tianyu Wang It is a common phenomenon during CBM drilling and production that reservoir damage is not eliminated completely. In view of this, a technical idea of composite pulsating hydraulic fracturing of radial horizontal wells which is conducive to blockage removing and stimulation was put forward in this paper. Speaking of the hydraulic jetting in a multi-branch radial well, it is to conduct pulsating hydraulic fracturing moderately through a high-diversion radial hole, so as to crush and break coal beds near the main hole to the uttermost. Thus, an extensive pressure relief and permeability increase area where high-diversion pathways are combined with fracture networks is formed. Then, to verify its technical principles, laboratory tests on pulsating hydraulic fracturing of radial wells were designed and carried out. Besides, the relationships of the features of acoustic emission (AE) response during the formation of fractures by composite fracturing of radial horizontal wells vs. coal breaking degree and macro fracture morphology were experimentally studied by using a pulse servo fatigue testing machine and an acoustic emission detector. And the following research results were obtained. First, under experimental conditions, fractures initially occur when the pressure of composite pulsating hydraulic fracturing of radial horizontal wells is 1/3–1/4 of the peak pressure of conventional fracturing, and the amount of its AE events is 1.38–7.07 times that of conventional fracturing. Second, when composite pulsating hydraulic fracturing of radial horizontal wells is conducted, AE emission signals respond strongly, the peak pressure for macro fracturing is lower and a larger fracture network can be generated more easily under the same condition. Third, radial laterals amount, borehole length, dynamic loading frequency and amplitude are the important factors affecting the effect of composite pulsating hydraulic fracturing of radial horizontal wells. In conclusion, composite pulsating hydraulic fracturing of radial horizontal wells provides a new idea of removing the blockages in CBM reservoirs and developing CBM efficiently, realizing effective blockage removing and stimulation of CBM wells.
       
  • A high-efficiency development mode of shale gas reservoirs in mountainous
           areas based on large cluster horizontal well engineering

    • Abstract: Publication date: Available online 15 March 2019Source: Natural Gas Industry BAuthor(s): Deli Gao With the basic characteristics of conventional horizontal wells, the so-called complex wells including horizontal extended-reach wells, multi-lateral horizontal wells, U-shaped wells, cluster horizontal wells, etc., are advanced well types for the efficient development of low-permeability, unconventional, deep-water, and deep oil and gas reservoirs, which have been highly concerned all over the world. Significant progress at home and abroad has been made in relevant researches and practices and is expected to play an important role in the efficient development of shale oil and gas. To meet the basic needs of environment & safety, land conservation, cost reducing and efficiency improving, it is urgent to create a unique and efficient mode for developing shale gas. Therefore, an efficient shale gas development mode for mountainous areas and an engineering and technical support system are presented based on large cluster horizontal-well engineering. An equation is thus obtained for calculating the maximum number of horizontal wells arranged allowably in “Well Factory” on a single platform. The general research and development of large extended-reach well technology are analyzed by expounding the basic concept of an extended-reach well and its drilling extension limit. And a calculation method is thus established to predict the maximum measured depth of open hole in extended-reach drilling. Moreover, some relevant research results and their significance for downhole tubular mechanics & mechanical extension limits in extended-reach drilling are also briefly introduced in this paper. The conclusions are drawn that, by following the idea of “integration of geology and engineering” in oil and gas development, these research results have a foreseeable application prospect in shale gas development in the mountainous areas in the future, and will contribute to new progress in China's “Shale Revolution”.
       
  • An experimental study on oxidizer treatment used to improve the seepage
           capacity of coal reservoirs

    • Abstract: Publication date: Available online 15 March 2019Source: Natural Gas Industry BAuthor(s): Yili Kang, Yingqian Tu, Lijun You, Xiangchen Li, Fansheng Huang It is difficult to stimulate coal reservoirs in physical approaches, and the recovery factor of coalbed methane (CBM) can be enhanced by applying strong oxidizers through oxidation to stimulate coal reservoirs. At present, however, there have been very few studies on the oxidation of CBM and fewer experimental studies for systematically evaluating the effect of oxidation on the seepage capacity of coal reservoirs. In this paper, the coal samples taken from coal seams of the Jurassic Xishanyao Formation in the Heishan Coal Mine, Toksun, Xinjiang, were selected as the study objects. Hydrogen peroxide solution immersion experiments were carried out on columnar and powdered coal samples, respectively to measure the permeability of columnar coal samples, the dissolution rate of powdered coal samples and the property parameters of hydrogen peroxide solution. Then, the reaction mechanisms between coal samples and hydrogen peroxide and the mechanisms to improve the seepage capacity of coal reservoirs were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM), infrared spectrum and wetting angle measurement. Finally, the stimulation effect of oxidation was compared with that of acidification. The following research results were obtained. (1) The permeability of coal samples is increased significantly after oxidation to 1.4–3.2 times the original permeability. (2) A large number of micro-fractures and dissolved pores are formed in the coal samples after oxidation, and consequently pore connectivity is improved greatly. Thus, the amount of associative hydroxyl and carboxyl functional groups on the surface of the coal samples increases, and the water wettability on the surface reduces. (3) Organic matters and pyrites are oxidized and consumed easily, and the generated H+ and micro-molecular aliphatic acids further dissolve inorganic mineral components. (4) Oxidation also has the advantage of acidification for dissolving inorganic mineral components, so there is a low and controllable probability of generating coal powder. In conclusion, applying strong oxidizers has the potential to become a new technology for coal reservoir stimulation.
       
  • A CBM development well type optimization method based on the long-run
           marginal cost

    • Abstract: Publication date: Available online 15 March 2019Source: Natural Gas Industry BAuthor(s): Youjin Dai, Shiqun Li, Liangyu Xia, Jingxin Li, Yang Lü Reasonable optimization of development well type is the prerequisite to realize the economic and effective development of coalbed methane (CBM). However, the existing CBM development well type optimization methods are disadvantageous in many aspects. CBM is a kind of typical unconventional natural gas resource, and its study focuses on single-well evaluation. In this paper, the assessment method and the evaluation index (EI) for CBM development well type optimization based on the long-run marginal cost (LRMC) were constructed on the basis of CBM characteristics from the perspective of economic feasibility. Then, the corresponding decision making criteria were established. Finally, this newly developed method was applied to the well-type optimization of different development blocks in two important CBM development basins in China. And the following research and application results were obtained. First, under the current technical and economic conditions, both directional well and horizontal well are economically feasible to the development of Block A in the Qinshui Basin and Block B in eastern margin of the Ordos Basin, and the economically optimal well type is a horizontal well in Block A and a directional well in Block B. Second, compared with single-well steady daily gas production and single-well investment, the evaluation results on the schemes of different well types present critical value, above which the economic benefit of different schemes are equivalent. Third, EI of different well types is affected by many factors, e.g. geological characteristic of gas reservoirs, single-well production profile, CBM selling price, investment and cost. Therefore, it is necessary to carry out dynamic analysis and update in time based on the change of various influential factors so as to ensure the rationality of decision-making. In conclusion, this newly developed method is intrinsically consistent with traditional evaluation methods, and it is more advantageous with strong operability, intuitive evaluation results and quick and accurate optimization of CBM development well types.
       
  • Factors influencing biogenic gas production of low-rank coal beds in the
           Jiergalangtu Sag, Erlian Basin

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Hao Chen, Yong Qin, Ze Deng, Meng Geng, Guizhong Li, Guangjie Sang, Daping Xia The study on the factors influencing the biogenic gas production of low rank coal beds is of great significance to the search of the favorable biogenic gas enrichment areas of similar coal beds and the guidance of the microbial stimulation technologies. In this paper, the lignite samples taken from the Jiergalangtu Sag in the Erlian Basin were selected to carry out the simulation experiment of biogenic coalbed methane under different temperatures, pH values, oxidation-reduction potentials (Eh) and trace element concentrations. Then, the influences on biogenic gas production were discussed and the optimal biogenic gas production condition was determined. And the following research results were obtained. First, in the simulation experiments, the biogenic gas production of coal beds increases first and then decreases with the increase of temperature, pH and trace element concentration and the decrease of Eh. Second, in the case of temperature 30–35 °C, pH 7.0–7.5 and Eh −225 mV, the metabolism of methanogen is the most active and the most favorable for the generation of biogenic gas, so biogenic gas production can be promoted by adding the trace elements (Fe2+ and Ni2+) of proper concentration. It is concluded that a proper burial depth (300–600 m), a weak runoff hydrodynamic condition and an anaerobic environment constitute the favorable conditions for the generation of biogenic gas in the Jiergalangtu Sag, Erlian Basin. Moreover, the addition of appropriate trace elements can be an effective means of microbial stimulation.
       
  • Unconventional casing programs for subsalt ultra-deep wells with a complex
           pressure system: A case study on Well Wutan 1 in the Sichuan Basin

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Lingzhan Zou, Yuncai Mao, Wenzhong Liu, Haige Wang, Jianhua Guo, Chuanguang Deng, Youcheng Zheng, Hongchun Huang, Jie Li, Hong Yue, Gang Chen Well Wutan 1 is a wildcat well deployed in the Dazhou–Kaijiang paleo-uplift, eastern Sichuan Basin and its design depth is 7570 m. The Cambrian and Sinian strata are its main exploration targets, and the strata below the Silurian in this well are geologically uncertain with a high risk. A large section of gypsum-salt layer may be encountered in the Cambrian and the longitudinal pressure system is complex. It is predicted that the bottom hole temperature is up to 175 °C, and the bottom hole liquid column pressure exceeds 140 MPa, and there is hydrogen sulfide. As a result, the casing program design is confronted with great challenges. In this paper, the difficulties and risks of drilling engineering were analyzed. Then, a casing program was designed and optimized referring to the successful drilling experience of subsalt ultra-deep wells at home and abroad, combined with the pressure system characteristics of Well Wutan 1 and the creep performance of gypsum-salt layers. Finally, the casing program was applied on site. And the following research results were obtained. First, in order to prevent lost circulation, blowout and differential pressure induced stuck pipe in the open hole section, it is determined that the casing program shall be in the pattern of six-section casing with 5 setting points. Second, no setting point is needed in the Carboniferous pressure depleted reservoir for it is lithologically tight and differential pressure induced stuck pipe and lost circulation are less risky. Third, to better isolate the salt layer, one section of casing is specially designed for the Cambrian gypsum-salt layer and its collapse strength is 160 MPa to prevent collapse by salt creep. Fourth, Well Wutan 1 is drilled successfully to the expected strata and its total depth is 8060 m. In conclusion, the unconventional six-section casing program with 5 setting points to ensure the subsalt drilling safety in the eastern Sichuan Basin is rational. The successful drilling of Well Wutan 1 provides experiences and references for the follow-up exploration of deep-seated gas in the Dazhou–Kaijiang paleo-uplift.
       
  • Optimal selection and effect evaluation of re-fracturing intervals in
           shale gas horizontal wells

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Yanchao Li, Yunbin He, Jianfeng Xiao, Xiaozhi Shi, Qiang Feng, Congbin Yin The monitoring results of production logging show that almost one third of perforation clusters produce no or less gas after volumetric fracturing is initially applied in shale gas reservoirs. Besides, the production decline after the commissioning is commonly faster. In this paper, a fracture network prediction model and a fracturing well productivity prediction model were established based on microseismic interpretation data and hydraulic fracture network propagation results. After petrophysics, microseism, production performance were taken into consideration comprehensively, shale re-fracturing development potential evaluation index (RDPEI) was proposed. Then, a re-fracturing design and evaluation method was developed and targeted interval selection and evaluation was realized and applied on site. And the following research results were obtained. First, due to the heterogeneity of natural fractures, hydraulic fracture networks are more different, so an obvious “dead gas zone” can be easily formed and its re-fracturing potential is high. Second, the initial hydraulic fracture network is more affected by natural fractures. The main part of a fracture network propagates along the direction of maximum horizontal major stress, the fractures in regional stimulated intervals propagate in the form of double wing, and the length of a liquid swept fracture network is 52–70% of seismic interpretation result. Third, the RDPEI model avoids the limitations of single factor analysis and realizes the quantitative prediction on three types of indexes of recoverability, compressibility and re-fracturing. Fourth, re-fracturing of the case well is remarkable in stimulation effect. Its shale gas productivity is increased by 38.9%, and its cumulative gas production in one year is increased by 62.5%. In conclusion, re-fracturing is an effective and feasible method for improving the single well ultimate recovery reserves of shale gas. This method provides a theoretical and technical support for the selection and effect evaluation of re-fracturing intervals in shale-gas horizontal wells.
       
  • Influence of reservoir primary water on shale gas occurrence and flow
           capacity

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Zhiming Hu, Xianggang Duan, Yabin He, Jianfa Wu, Jin Chang, Li Liu, Kang Wu, Zhenyong Ma In this paper, shale samples of Lower Silurian Longmaxi Fm, taken from the Changning–Weiyuan area in the Sichuan Basin, were selected to figure out the influence of reservoir primary water on the adsorption laws and the flow capacity of shale gas. Experimental samples with different water saturations were prepared using the adsorption equilibrium method. Then, high-pressure isothermal adsorption experiments were carried out, and the isothermal adsorption effects and mechanisms of shale under different water saturations were discussed. Finally, the flow capacity of shale gas under different water saturations was tested using the independently developed steady-state flow test device. And the following research results were obtained. First, the presence of primary water in micron–nanometer pores of shale reservoirs reduces the adsorption capacity of shale. When the water saturation is 40%, the simulated total gas content is 18% lower than that in the conventional calculation result. Second, the apparent shale permeability is a function of pressure. Due to the effect of Knudsen diffusion, the apparent shale permeability increases significantly with the decrease of pressure under low pressure. When the average pressure is 5 MPa and the water saturation reaches 50%, the apparent shale permeability is about 70% lower than that of a dry sample. Third, when the water saturation is lower than the critical value, water is mainly presented as non-movable water in micropores and mesopores, and it has less effect on the flow capacity of shale gas. When the water saturation is greater than the critical value, the lodging point of water is changed, resulting in significant reduction of the shale gas flow capacity. It is concluded that an accurate understanding of the original water saturation and critical water saturation of shale reservoirs helps to calculate shale gas reserves accurately and predict gas well production rate rationally.
       
  • Simulation of effective fracture length of prepad acid fracturing
           considering multiple leak-off effect

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Lurui Dang, Changlin Zhou, Mei Huang, Desheng Jiang For the purpose of improving the accuracy and effectiveness of acid fracturing design for carbonate reservoirs with developed natural fractures, an acidizing fluid flow and reaction model taking the multiple leak-off effect of natural fracture, wormhole and matrix into account was established according to the liquid phase reaction equilibrium principle and the local reaction equilibrium principle after the dynamic change of fracture geometry in the process of fracture created by prepad fluid was simulated in the classical pseudo-three dimensional mathematical model of fracture propagation. Then, the acid fracturing stimulation of a case well on site was taken as an example. The newly developed model was used to simulate the filtration process of acidizing fluid in fractures and the dynamic etching morphology of acidic rocks during the acidizing fluid injection of prepad acid fracturing. The effective length of etched fractures was determined by analyzing the concentration change of acidizing fluid along the direction of hydraulic fracture length and the threshold concentration of residual acidizing fluid comprehensively, and then it was compared with the interpretation result of pressure buildup test. And the following research results were obtained. First, in the process of acid fracturing in fractured–porous reservoirs, the acidizing fluid filtration velocity along the direction of fracture length is not constant and the filtration velocity curve fluctuates in a serrated shape. And the acidizing fluid filtration velocity where etched wormholes meet natural fractures is commonly higher than that in matrix. Second, acidizing fluid is lost seriously and the effective distance of acidizing fluid gets short significantly during the acid fracturing of fractured–porous reservoirs. Third, acid fracturing in the verification well is remarkable in blockage removing and stimulation, and its well test interpretation results are consistent with the simulation interpretation results provided by the newly developed mathematical model. It is indicated that this newly developed model is reliable. In conclusion, the mathematical model of prepad acid fracturing which considers multiple leak-off effect is more suitable for acid fracturing simulation of fractured–porous reservoirs.
       
  • Logging-based identification and evaluation of karst fractures in the
           eastern Right Bank of the Amu Darya River, Turkmenistan

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Shudong Zhang, Xingguo Ren, Li Luo, Tingliang Guo, Xusheng Liang Carbonate gas reservoir in the eastern area on the Right Bank of the Amu Darya River, Turkmenistan, are of low-porosity and with developed fractures. In this area, fractures control reservoir properties and natural gas production, and karst fractures are the most important kind of fractures, so their identification and evaluation are quite necessary. In this paper, fracture types were identified and their occurrence was extracted by using conventional logging and image logging data after core calibration. Then, the distribution characteristics of karst fractures and their controlling effect on reservoirs were studied according to the identification results. And the following research results were obtained. First, karst fractures are mainly of high angle with the characteristic of mono system and the interactive relation of genesis. Second, they are mainly distributed in the upper XVhp layer of Callovian–Oxford Stage and the lower XVa2–XVI layer. Third, they are the main effective fractures in this area. The dissolved pores are connected effectively through the expanded karst fractures by dissolution, and consequently reservoirs of high porosity and permeability are formed and they are the important reservoir type and high-yield gas reservoir in this area. Fourth, karst fractures are related to high-yield wells and high-yield layers in this area, and they also control the distribution of high-yield reservoirs in the lower part of Callovian–Oxford Stage. It is concluded that by virtue of imaging logging and conventional logging data, karst fractures, unfilled fractures, semi-filled fractures and fully filled fractures can be identified and evaluated better. Furthermore, the identification and evaluation of karst fractures deepen the understanding on fractured reservoirs in this area, improve the reservoir evaluation effect, and provide the basis for the target horizon and azimuth optimization of horizontal wells and highly deviated wells. And it is also indicated that the reservoirs with developed karst fractures are the subsequent important drilling targets.
       
  • Effect of cross-section distortion on the performance of small-radius
           induction bends

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Gaofeng Wang, Zhuanzhao Yang, Yinglai Liu, Xianghui Nie, Yan Xu, Jinlan Zhao While a small-radius induction bend is manufactured, various cross-section distortions may occur, such as its cross section tending to be elliptic, and wall thickness reduction or increase. These defects may deteriorate the bearing capacity of pipelines. In order to study the effect of cross-section distortion on the performance of small-radius induction bends, 3D (D refers to pipe diameter) induction bends were manufactured based on different combinations of process parameters. Then, the cross-section distortion, structure properties and their correlation of 3D bends and conventional 5D bends were analyzed comprehensively by means of cross-section geometry analysis, distortion analysis, physical and chemical property test, micro-structural analysis and so on. The following results were obtained. First, the wall thickening/thinning rate of 3D bends is about 2 times that of 5D bends, and the roundness of 3D bends is about 2–4 times that of 5D bends. Second, the cross-section distortion of 3D bends is obvious, so its heating temperature varies greatly in different parts, leading to different structure morphologies and contents. As a result, the numerical distribution of mechanical properties of each part of 3D bends (e.g. intrados, extrados and neutral zone) is discrete. Third, the strength at the intrados of most bends doesn't meet the standard, and it is sorted form the higher to the lower as extrados, neutral zone and intrados while the sequence of Charpy impact toughness is right contrary to the strength. Fourth, the strength at intrados and extrados decreases with the increase of roundness. The strength at intrados decreases with the increase of thickening rates. And the strength at extrados increases with the increase of thinning rates.
       
  • New understanding of the sedimentary model of Lower Cambrian Longwangmiao
           Formation reservoirs in the Sichuan Basin

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Wei Yang, Guoqi Wei, Wuren Xie, Mancang Liu, Hui Jin, Fuying Zeng, Nan Su, Ai Sun, Juehong Shen, Shiyu Ma Natural gas in the gas reservoirs of Lower Cambrian Longwangmiao Fm is mainly concentrated in the granular shoal facies in central Sichuan Basin, therefore the study on lithofacies paleogeography and the prediction on granular shoal distribution are the key to improving the success ratio of natural gas exploration in this area. In this paper, outcrop, drilling, seismic and logging data were studied comprehensively. Subsequently, the sedimentary facies and sedimentary model of Longwangmiao Formation in the Sichuan Basin and its adjacent areas were studied, and lithofacies paleogeographic maps were prepared based on previous research results. Besides, “three-shoal” sedimentary model of Longwangmiao Fm was established, the distribution range of three shoal belts was predicted and their development characteristics and main controls were analyzed, thereby pointing out the direction and field of natural gas exploration in the next stage. It is indicated from the research results that: first, the paleogeographic pattern of the Sichuan Basin in the Longwangmiao period was represented as a rimed carbonate rock platform, with the developments of sedimentary facies such as mixed tidal flat, restricted platform, open platform, platform margin and slope facies. Second, the “three-shoal” sedimentary model of Longwangmiao Fm was established. One of them is the granular shoal in platform margin facies and is distributed along the eastern margin of the Sichuan Basin. The other two are intra-platform granular shoals which were distributed on the east and west sides of lagoon subfacies, belonging to restricted platform facies and open platform facies, respectively. Third, the granular shoal of restricted platform facies is the main reservoir of Longwangmiao Fm gas reservoir in the Anyue Gas Field. It is distributed in central Sichuan, and its development is controlled by lagoons and Gaoshiti–Moxi Paleo-uplift. Fourth, the platform margin granular shoal is mainly distributed along the northern and eastern margins of the basin, and its development is controlled by the slope break of sedimentary paleogeomorphy. In conclusion, the granular shoal of restricted platform facies and shoal of platform margin facies are good reservoirs that they are the important fields of natural gas exploration. Furthermore, the new understanding to “three-shoal” sedimentary model and granular shoal distribution of Longwangmiao Fm is of great theoretical significance to the study on sedimentary systems of ancient strata.
       
  • Negative adsorption in the isotherm adsorption experiments of
           low-adsorption coal and shale

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Wenguang Tian, Ze Deng, Hongyan Wang, Honglin Liu, Guizhong Li, Xuejun Liu, Zhenhong Chen, Hao Chen, Yanan Li Negative absorption of an inverse V type which rises first and then drops is often observed in the adsorption test of low adsorption samples. In view of this, a gravimetric isotherm rig with a large sample size was introduced. Its testing principles and operation processes were analyzed based on the previous research results. Then, the volumetric method, magnetic-levitation gravimetric method and large sample size gravimetric method were compared in terms of their advantages and disadvantages. Accordingly, this gravimetric isotherm rig with a large sample size was adopted to perform isotherm adsorption experiments on the low-rank coal samples taken from Well Jimei 2 in the Jiergalangtu sag, Erlian Basin, Inner Mongolia, and shale samples from the Lower Silurian Longmaxi Fm in the southern Sichuan Basin, so as to explore the essential reason for the “negative adsorption” after the effect of a systematical cumulative error is eliminated. And the following research results were obtained. First, when the large sample size gravimetric method is adopted, the phenomenon of “negative adsorption” doesn't occur and the test results of low-rank coal and shale samples are reliable with a high fitting degree (R2 > 0.99). Second, an electronic sensor error (e.g. electronic balance and P&T sensors), a system cumulative error and an adsorbed phase density error are not the factors leading to the reversal of negative adsorption curves. Third, the void volume error of a sample cell is the essential reason for the negative adsorption. In conclusion, the test accuracy can be improved by introducing the volume correction factor into the isotherm adsorption interpretation algorithm.
       
  • Influence of sloshing on the performance of a trough plate redistributor

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Jianfeng Tang, Jian Cui, Qingyan Xing, Weiming Zhang, Xinming Jin, Pengfei Ma A packed tower is one of the components of offshore floating liquefied natural gas (FLNG) storage and unloading device. In order to ensure the good redistribution performance of a gas–liquid redistributor in the packed tower, we developed a set of experimental devices which can realize different sloshing conditions and different bias current incoming forms and a corresponding numerical calculation model by combining hydraulic experiments with hydromechanic numerical simulation. Then, the simulation results were verified by using the experimental results, and simulation results and experimental results were analyzed. Finally, the performance of the traditional trough plate redistributor was investigated under the working conditions of quiescence, sloshing and different bias current incoming. And the following research results were obtained. First, under the working condition of quiescence, the liquid flow rate of different sprinkling points on the traditional trough plate redistributor is basically the same and the uniform distribution is presented with the non-uniformity in the order of 10–2. Second, the reason for the uniform redistribution deterioration of the redistributor is mainly the liquid level difference caused by the liquid migration. Third, under the working conditions of quiescence, rolling and pitching, the uniform distribution of trough plate redistributor is rarely affected by the change of bias current degree of the incoming liquid. Under the working condition of sloshing 5°, the non-uniformity difference of the overall orifice flow rate between the liquid incoming in the whole area and that in 2/3 area is less than 5%. Fourth, the non-uniformity of the overall orifice flow rate in the trough plate redistributor is more affected by rolling and pitching. The non-uniformity of the overall orifice flow rate rises to over 0.5 under the working condition of rolling 5° and over 0.3 in pitching 5°. It is indicated that under the working condition of sloshing 5°, the uniform distribution of trough plate redistributor is poor not only in the case of whole area liquid incoming but also in the case of bias current incoming, and it is affected more by sea conditions. In conclusion, the traditional trough plate redistributor is poorly adaptive to the sloshing at sea.
       
  • Development of Keshen ultra-deep and ultra-high pressure gas reservoirs in
           the Kuqa foreland basin, Tarim Basin: Understanding and technical
           countermeasures

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Tongwen Jiang, Xiongwei Sun The Keshen Gas Field in the Kuqa foreland basin, Tarim Basin, is a rare fractured tight sandstone gas reservoir with ultra-depth and ultra-high pressure. During its pilot period of gas field development, the development effect is poor with a low development well success rate, a low utilization rate of production capacity and a rapid decline of gas well productivity. In view of these problems, development experiments and technological researches were carried out continuously after the geological characteristics of gas reservoirs, productivity control factors, reservoir connectivity, seepage characteristics, gas and water relations and water invasion laws were studied thoroughly. And consequently, the development countermeasures of “well placement in high position, moderate stimulation and early-stage drainage” were prepared, and five matching development technologies were formed, such as description technology of ultra-deep complex structures, well pattern optimization technology for fractured tight sandstone gas reservoirs, fracture net acid fracturing technology for fractured tight sandstone reservoirs, dynamic monitoring technology for ultra-deep and ultra-high pressure gas wells, wellbore integrity management and evaluation technology for high pressure gas wells. The following remarkable application results were achieved in the process of gas field development. First, the drilling depth error of the target formation drops from 125 m to less than 30 m. Second, the utilization rate of production capacity in the Keshen 8 Block reaches 100%. Third, the average absolute open flow rate is increased by 5 times to 273 × 104 m3/d from 50 × 104 m3/d before the stimulation. Fourth, safe and smooth production under high temperature and high pressure conditions is realized in the Keshen Gas Field. In conclusion, the successful and efficient development of the Keshen Gas Field provides experiences for the development of similar gas reservoirs at home and abroad, and its development countermeasures and matching technologies have important guidance and reference significance.
       
  • Influence of reservoir heterogeneity on water invasion differentiation in
           carbonate gas reservoirs

    • Abstract: Publication date: January 2019Source: Natural Gas Industry B, Volume 6, Issue 1Author(s): Xi Feng, Xian Peng, Longxin Li, Xuefeng Yang, Juan Wang, Qian Li, Chun Zhang, Hui Deng Diversified heterogeneities tend to occur in carbonate gas reservoirs due to different scales and distribution densities of pores, vugs and fractures in reservoirs, and consequently the water invasion laws of gas reservoirs are more different. In this paper, the methods quantitatively describing the matching relationships between pores, vugs and fractures were improved based on full-diameter core digital processing and analysis so as to understand the heterogeneity of carbonate reservoirs and its influence on the water invasion laws of gas reservoirs and then predict the water invasion dynamics of gas reservoirs. Firstly, a new method to evaluate the contribution of microfractures to reservoir seepage capacity was established according to the analysis chart of percolation theory. Then, gas–water relative permeability and rock compressibility were measured by conducting gas/water seepage and fluid–solid coupling stress sensitivity experiments under the conditions of actual gas reservoir pressure and temperature. And accordingly the effects of various fractures and caves on the gas invasion laws of gas reservoirs were analyzed. Finally, the method to predict the differentiation characteristics of water invasion influence of the reservoirs with different types of physical properties was developed based on the water invasion characteristics of typical carbonate gas reservoirs in the Sichuan Basin. The following research results were obtained. First, in a broad sense, different types of carbonate reservoirs are classified as a triple continuum. The development of fractures speeds up the appearance of water invasion in gas reservoirs while the uniform development of caves slows down the appearance of water invasion effect. Second, the development of microfractures is a prerequisite for ultra-low porosity reservoirs to possess the ability of medium permeability or high permeability. The water invasion law in this case is obviously different from the channeling along large fractures or the water invasion in the network small fracture development belt. Third, the stress sensitivity of reservoir porosity in aquifer is the main source of formation water invasion energy. This characteristic is more prominent in the early stage of the exploitation of abnormal high pressure gas reservoirs. The research results have been applied to water invasion energy assessment, water invasion performance forecast and water control measure effectiveness prediction in a number of carbonate reservoirs in the Sichuan Basin. And they provide effective technical guidance for water invasion control in complex gas reservoirs and further understanding of water invasion differentiation laws.
       
  • Migration and distribution of complex fracture proppant in shale reservoir
           volume fracturing

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Linhua Pan, Ye Zhang, Lijun Cheng, Zhaohui Lu, Yuanbo Kang, Pei He, Bingqiang Dong In this paper, a large-scale experimental system was established to identify the migration and distribution laws of complex fracture proppant in shale reservoir volume fracturing. With this system, the effects of secondary fracture angle, fluid displacement, proppant concentration and size, fracturing fluid viscosity and other factors on the migration and distribution of proppant were tested, and the migration and distribution of proppant in primary/secondary fractures were analyzed. The following results were obtained. First, the fluid flow pattern in fractures transforms gradually from laminar flow into turbulent flow with the increase of fracture supporting height. Second, the migration modes of proppant in fractures mainly include suspended migration and gliding migration. Third, the distribution form of proppant in primary fractures before branching is related to secondary fracture angle, fluid displacement and proppant concentration and size, among which the fluid displacement is the most important factor. Fourth, the mass ratio of proppant in primary fractures after branching is proportional to the secondary fracture angle, fluid displacement, fracturing fluid viscosity and proppant concentration and size, and is inversely proportional to the flow ratio between secondary fractures and primary fractures. Fifth, the mass ratio of proppant in secondary fractures after branching is proportional to fluid displacement, fracturing fluid viscosity and flow ratio between secondary fractures and primary fractures, and is inversely proportional to secondary fracture angle and proppant concentration and size. Sixth, the angle at the leading edge of proppant bank in the primary fractures after branching is proportional to the proppant concentration and size and the flow ratio between secondary fractures and primary fractures, but is inversely proportional to secondary fracture angle, fluid displacement and fracturing fluid viscosity. Seventh, the angle at the leading edge of proppant bank in the secondary fractures after branching is proportional to the secondary fracture angle and the proppant concentration and size, but is inversely proportional to the fluid displacement, fracturing fluid viscosity and flow ratio between secondary fractures and primary fractures. In conclusion, the research results can provide a theoretical support for proppant optimization and program design of shale reservoir volume fracturing.
       
  • Progress and prospects of natural gas development technologies in China

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Ailin Jia Under the present situation of low global oil prices and vigorous development of green energy resources, China has turned to focus on natural gas in oil and gas sector, both production and consumption of which are soaring high these days and the role of which is gradually prominent in energy sources. With the aims to help promote the further rapid development of natural gas business in China, this paper analyzed natural gas development process and summarized the new advances in natural gas development technologies in the recent years. On this basis, this paper analyzed the prospects of natural gas development in China in the four aspects of production rates, demand potential, import volume, future position of natural gas. The following results were obtained. (1) Since the 12th Five-Year Plan, natural gas business has been doing well with a rapid increase of consumption, diversified supply sources, steadily increasing of reserves and production rates, obviously satisfactory benefits from exploitation. (2) Breakthroughs have been made in technical bottlenecking problems with an improved innovation capacity in the respects of deep-strata gas development, large-scale gas field development adjustment, tight-gas recovery enhancement, development of shale and CBM gas, engineering techniques, and development strategies support system. (3) With the deepening of development, influenced by policies, environment concerns and geological conditions, continuous efficient natural gas development will face up with such challenges as lower ratio of quality reserves, higher gas field development expenses, more difficult benefit development of unconventional gas reservoirs, further compressed upstream benefits, less stable production capacity of those major gas fields, increasingly fierce competition in the energy market, etc. In conclusion, it is demonstrated that natural gas development in China will enter into a new stage of attaching equal importance to both unconventional and conventional gas; natural gas demand potential will be great and its consumption structure will become more diversified; gas imports will rise year by year, resulting in the vigorously increasing external dependency; and natural gas will become the main growth engine in the process of energy mix adjustment.
       
  • Development and field application of a pulse-jet hydraulic impactor

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Wei Li, Shichang Li, Lipeng Yan, Dong Qin, Shihui Sun, Huan Zhao The current studies on hydraulic pulse jet mainly focus on the pulse jet flow field and its effect, but have never extended to the collaboration of hydraulic impact and pulse jet for rock breaking. In this paper, both hydraulic impact and pulse jet were combined effectively to develop a pulse-jet hydraulic impactor for drilling after analyzing the working principles and realization conditions. The rock-breaking capacity of this tool was verified through laboratory experiments and field tests. The following results were obtained. First, the tool can run when the weight of the impactor body is less than 60 kg. Second, the rock-breaking capacity of the drilling borehole assembly (BHA) under the synergistic action of hydraulic impact and pulse jet is obviously better than that of other drilling tools, and the tool is much more efficient than other tools in ROP enhancement. Third, the impact effect is dependent on the weight and impact frequency of the impactor and the impactor with the weight of 30 kg is better in impact effect. Fourth, the larger the impulse jet, the higher its rock-breaking capacity is. The pulse jet can be increased by reducing the diameter of the tool's nozzle. Fifth, hydraulic impact can help accelerate the breaking of high-hardness rocks, and the breaking of less-cemented rocks can be greatly enhanced by increasing the pulse jet. Field application results show that the ROP of the drilling tool based on the collaboration of hydraulic impact and pulse jet is 2.52 m/h, which is 72.5% higher than that of conventional BHAs. It is concluded that this developed pulse-jet hydraulic impactor provides a new idea to solve the problems in deep wells and horizontal wells, such as low drilling speed, obvious chip hold down effect and difficult cuttings removal.
       
  • Significance of paleo-fluid in the Ordovician–Silurian detachment zone
           to the preservation of shale gas in western Hunan–Hubei area

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): An Liu, Wenjia Ou, Huilan Huang, Kai Wei, Hai Li, Xiaohong Chen The studies on the paleo-fluid in the Ordovician–Silurian detachment zone in the Middle–Upper Yangtze area focus on the origin of high-density methane inclusions and the evolution process of formation pressure, but rarely deal with the significance of paleo-fluid to shale gas preservation. In this paper, the relationship between fracture formation and detachment zone was analyzed by observing the Ordovician–Silurian outcrops in western Hunan–Hubei area and by investigating the geological characteristics of fracture veins in the drilling cores. Then, the significance of paleo-fluid forming environment and detachment zone to shale gas preservation was studied by using inclusion compositions of fracture veins and homogenization temperature test data. Finally, accumulation–dispersion modes of shale gas in the detachment zone were established. The following results were obtained. First, the detachment zone is lithologically composed of silicite with intercalated shale at the Ordovician–Silurian interface. In the detachment zone, rocks are broken and small crumples are developed. The conjugate-vertical joints are relatively developed in the silicite above and below the detachment zone. Second, multi-stage and multi-type inclusions, especially the aqueous inclusions, are developed in the veins of the detachment zone. Third, the infiltration depth of ancient meteoric water along the detachment zone in the study area is over 4000 m. High-density overpressure methane inclusions were captured in the detachment zone during early stage, while normal-pressure methane and nitrogen inclusions were captured during late stage. Fourth, the ionic constituents of inclusions recording the fluid activity during the late stage was characterized by high sodium-chloride coefficient, high desulfurization coefficient and low metamorphic coefficient, and it is indicated that the sealing capacity of the shale in the detachment zone gets worse. Fifth, the accumulation and dispersion of shale gas in the detachment zone within the study area is divided into three modes, i.e., syncline, broad anticline and closed anticline. In conclusion, the detachment zone in the study area is permeable. Synclines and closed anticlines developed in detachment structures are unfavorable for the accumulation of shale gas, while broad anticlines are favorable.
       
  • Authigenic embrittlement of marine shale in the process of diagenesis

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Honglin Liu, Wei Guo, Dexun Liu, Shangwen Zhou, Jixin Deng Studies on the origin of shale brittleness are of great significance to understanding shale gas accumulation laws. The current studies, however, mostly focus on the improvement of shale brittleness by biological quartz enrichment, but rarely on the recrystallization of quartz in the process of diagenetic evolution. In this paper, a series of researches were carried out on the Lower Silurian Longmaxi Fm marine shale in the Changning block of the Sichuan Basin. Firstly, shale pore, mineral component and bedding characteristics were observed by means of cathodoluminescence (CL), scanning electron microscope (SEM) and so on. Then, the control effects of quartz origin, overpressure environment and diagenetic evolution on shale brittleness were investigated by analyzing the mineral composition and siliceous composition of shale microscopically. Finally, the authigenic embrittlement model of marine shale was put forward and the geological significance of authigenic microcrystalline quartz to the improvement of shale brittleness in the process of diagenesis was illustrated. The following results were obtained. First, during the sedimentation, burial and diagenetic evolution, shale experiences diagenetic changes which help increase quartz content and form concealed fracture networks, thus benefiting the formation of complex flow pathways in later stimulation. Second, organic matters play a positive role in improving shale brittleness in the process of geological evolution. It promotes the formation of authigenic microcrystalline quartz and improves the brittleness of shale. In conclusion, due to the authigenic embrittlement of shale in the process of diagenesis, rock structure is changed, rock strength is enhanced and shale porosity is preserved. Consequently, reservoir space in shale is improved and the enrichment state of shale gas is modified. Therefore, the preservation condition under the control of tectonic movement factors is vital to geological evaluation on shale gas. In addition, marine shale is certainly well brittle after authigenic embrittlement in the process of diagenesis as long as its organic matter content is abundant.
       
  • A new deliverability evaluation method of gas condensate wells in
           gas–liquid two-phase state

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Jialiang Lu, Hao Zhang, Baohua Chang, Wen Cao, Hedong Sun Gas well deliverability evaluation and analysis are challenging due to the frequent abnormalities of deliverability test data of gas condensate wells caused by seepage of oil and gas phases in the reservoirs. To this end, based upon the pseudo-single-phase seepage equation and the oil–gas two-phase seepage equation, a new deliverability evaluation method was established which is applicable to the following two cases when the flow of a gas well reaches the quasi-steady stage, i.e., the pseudo-single-phase stable point deliverability evaluation for the case when the formation pressure is above the dew pressure; the gas–liquid two-phase stable point deliverability evaluation for the case when the formation pressure is below the dew pressure. Using this established deliverability evaluation method, based on the basic parameters of the Yaha gas field, Tarim Basin, the IPR curves were first obtained of gas wells do not get this at the same production gas–oil ratio and at the formation pressure above and below the dew point pressure; then, according to the four condensate gas fields, such as Yaha, Tazhong I, Qianmiqiao and Dina 2, the absolute open flow (AOF) potentials of condensate gas wells under different gas–oil production ratios were calculated. Finally, through statistical analysis of the calculation results from typical wells, the following findings were obtained. This new deliverability evaluation method under the two states of condensate gas wells with quasi-single-phase and gas–liquid two-phase stable points can be used to avoid cases due to the oil–gas flow in a condensate gas well which has remained unresolved by the classical deliverability evaluation methods. Also, with the increase of gas–oil ratios in gas condensate wells, a variable discrepancy is gradually reduced in AOF potentials calculated respectively by the quasi-single-phase and gas–liquid two-phase stable point deliverability evaluation equations. For the condensate gas wells with high condensate content and low condensate gas production rates, the AOF potentials calculated by the gas–liquid two-phase stable point deliverability equation is more appropriate and reliable compared with that obtained by classical methods.
       
  • Change of water saturation in tight sandstone gas reservoirs near
           wellbores

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Hongyu Ma, Shusheng Gao, Liyou Ye, Huaxun Liu, Wei Xiong, Jianglong Shi, Lin Wang, Kang Wu, Qingshan Qi, Chunqiu Zhang Tight sandstone gas reservoirs commonly contain water, so liquid loading often appears near wellbores, leading to production decline and even shutdown of gas wells. Therefore, the study on the change of water saturation near wellbores is of great significance to understanding the water production mechanisms of gas wells. In this paper, a set of physical simulation experiment procedures of identifying the change of water saturation near wellbores was designed according to the principle of radial well seepage of gas wells, and the production performance after vertical well fracturing in gas reservoirs was simulated by connecting tight cores with a diameter of 10.5 cm, 3.8 cm and 2.5 cm in series in a descending order of distance. According to the depressurizing production mode of gas wells, tubes with small diameters of 20, 30, 40 and 50 μm were used to simulate gas well tubing to control the gas production rate. And the change of water saturation near wellbore in the process of depletion production and its influencing factors were investigated. Finally, combined with actual data of production wells, the water saturation and water production of gas wells near wellbores and in different zones were calculated at the above four different small diameters of tubes and the changes thereof were also analyzed. The following results were obtained. First, each gas production rate corresponds to a critical water saturation. When the initial water saturation is lower than the critical value, the formation water flowing near the wellbore and in the middle zone can be carried out along with the production of gas and no liquid loading is formed. Second, when the initial water saturation is higher than the critical value, a large amount of formation water migrating from the far-wellbore zones accumulates near the wellbore, and thus liquid loading occurs at the bottom hole. Third, when the initial water saturation is equal to the critical value, the higher the gas production rate is, the more easily liquid loading tends to form near the wellbore. Fourth, for the same water saturation, water production increases and recovery factor decreases with the increase of gas production rate. In conclusion, the cumulative water production chart of a gas well generated by the physical simulation experiment method proposed in this paper agrees well with the water production behavior of the corresponding gas well. The research results are conducive to the effective prediction of gas well water production and can be used as guidance for the reasonable gas well water control.
       
  • Injection–production mechanisms and key evaluation technologies for
           underground gas storages rebuilt from gas reservoirs

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Junchang Sun, Hongcheng Xu, Jieming Wang, Lei Shi, Chun Li, Ligen Tang, Rong Zhong Underground gas storages (UGSs) rebuilt from gas reservoirs is the most popular UGS type in the world. It accounts for 75% of the total active gas of all gas storages. In order to design more scientific and reliable geological schemes for constructing the underground gas storages rebuilt from gas reservoirs and optimize the UGS operation parameters, we analyzed the UGS basic characteristics of multi-cycle high-rate injection and production. Then, the dynamic sealing capacity of traps and the water–gas high-speed interactive flow mechanism of UGSs rebuilt from gas reservoirs with complex geological conditions were investigated by both physical simulation and numerical simulation. Finally, the key technologies for evaluating the dynamic sealing capacity of caprocks and faults and the storage capacity parameters were developed. Some results were obtained. First, the alternating stress in the process of UGS injection and production weakens the original static capillary sealing capacity and mechanical integrity of caprocks to different extents, and the trap sealing capacity can be quantified and evaluated comprehensively by using dynamic breakthrough pressures, shear safety indexes and other indicators. Second, a UGS capacity design method based on effective gas-bearing pores was developed according to the local pore-based recovery mechanism revealed in the high-speed gas–water mutual flooding test. Field application in the multi-layer UGS of H shows that these technologies provide an effective guidance for the design of geologic schemes. After five cycles of injection and production, its ramp-up ratio reached 91.8% and the peak shaving capacity increased quickly to 36.3 × 108 m3 from 2.7 × 108 m3 in the early stage of production. Moreover, the operation indicators matched well with the design.
       
  • Key technologies for salt-cavern underground gas storage construction and
           evaluation and their application

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Qiqi Wanyan, Guosheng Ding, Yan Zhao, Kang Li, Jingen Deng, Yali Zheng Salt-cavern underground gas storage is technically faced with non-uniform distribution of stratified salt rocks, complex solution mining mechanism, difficult control of solution mining process, less operation safety and stability of caverns and difficult reconstruction and utilization of old caverns. In view of these technical difficulties, the design concept was fully updated based on the design experience and field practice of Jintan gas storage in Jiangsu, for purpose of maximizing salt layer utilization ratio, improving solution mining efficiency, shortening construction time and ensuring cavity safety. Based on the updated design concept, five series of key technologies were proposed in site evaluation, cavern design and control, stability assessment and storage capacity parameter design, old cavern screening and utilization, and gas storage operation and monitoring. The following results were obtained from the actual application of these key technologies to the Jintan gas storage. First, the actual drilling coincidence rate of geological program is high. Second, the cavern is morphologically coincident with the design. Third, the cavern deformation retract rate is in line with the stability evaluation result. Fourth, old caverns are successfully reconstructed and utilized. Fifth, the arrangement of the monitoring network ensures the operation safety of salt-cavern underground gas storage and makes an important contribution to the peak shaving and supply guarantee of natural gas in the Yangtze River Delta region. In conclusion, the research results provide guidance for the design and engineering implementation of salt-cavern underground gas storage construction program, as well as a theoretical and technical support for the construction of similar gas storages.
       
  • Reservoir stability in the process of natural gas hydrate production by
           depressurization in the shenhu area of the south China sea

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Yizhao Wan, Nengyou Wu, Gaowei Hu, Xin Xin, Guangrong Jin, Changling Liu, Qiang Chen Reservoir stability is a key factor in the production of natural gas hydrate (NGH), and also a prerequisite to ensuring safe and efficient NGH production. However, it has been rarely discussed. To analyze the reservoir stability in the process of NGH production by depressurization in the Shenhu area of the South China Sea, we established a 3D geological model of NGH production by depressurization on the basis of NGH drilling data in this area, which was then discretized by means of nonstructural grid. Then, the mathematical model coupling four fields (i.e. thermal, hydraulic, solid and chemical) was established considering the heat and mass transfer process and sediment transformation process during NGH production. The model was solved by the finite element method together with the nonstructural grid technology, and thus the time-space evolution characteristics of reservoir pore pressure, temperature, NGH saturation and stress in the condition of NGH production by depressurization were determined. Finally, reservoir subsidence, stress distribution and stability in the process of NGH production by depressurization in the Shenhu area were analyzed. The results obtained are as follows. First, the higher the reservoir permeability and the larger the bottomhole pressure drop amplitude are, the larger the subsidence amount and the higher the subsiding speed. Second, as the reservoir pore pressure decreases in the process of production, the effective stress increases and the shear stress near the well increases obviously, resulting in shear damage easily. Third, the increase of effective reservoir stress leads to reservoir subsidence, which mainly occurs in the early stage of NGH production. After the production for 60 days, the maximum reservoir subsidence reached 32 mm and the maximum subsidence of seabed surface was 14 mm. In conclusion, the NGH reservoirs in the Shenhu area of the South China Sea are of low permeability and the effect range of reservoir pressure drop is limited, so the reservoirs would not suffer from shear damage in the sixty-day-production period.
       
  • Influence of sediment media with different particle sizes on the
           nucleation of gas hydrate

    • Abstract: Publication date: December 2018Source: Natural Gas Industry B, Volume 5, Issue 6Author(s): Baoyoong Zhang, Lihong Zhou, Changling Liu, Qiang Zhang, Qiang Wu, Qiong Wu, Chuanhai Liu In order to identify the effect of the particle size of sediment media on the nucleation of gas hydrate (hereinafter referred to as hydrate), we conducted gas hydrate nucleation kinetics experiments on six types of sediment media by using the high-pressure visualized reactor to measure the nucleation induction time of hydrates in sediment media with different particle sizes, based on the size of hydrate-bearing sediments in the Shenhu sea area of the South China Sea. Besides, the nucleation pattern of hydrates in sediment media was analyzed using the probability distribution function. Then, considering the effect of capillarity on the liquid-gas interfacial tension in the pores of sediments, a theoretical model for the pore radius of sediment-nucleation induction time of hydrates was established based on the Kashchiev model in combination with the Arrhenius equation. Finally, the calculation results of the theoretical model were compared with the experimental results. The following results were obtained. First, sediment media with larger particle sizes can help effectively shorten the nucleation induction time of hydrate and increase the concentration degree of induction time. Second, it is deduced from the theoretical model formula that, due to the interfacial tension of pores in the sediment, the nucleation induction time of hydrate increases and then decreases with the increase of sediment particle size, and there is a critical particle size. Third, there is a non-positive correlation between the sediment particle size and the change of hydrate formation difficulty. Within a certain range, the hydrate formation difficulty decreases gradually with the increase of sediment particle size. The research results provide a technical support for the exploration of marine gas hydrate deposits.
       
 
 
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