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Journal of Natural Gas Geoscience
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ISSN (Print) 2468-256X
Published by Ke Ai Homepage  [15 journals]
  • Review of the chemometrics application in oil-oil and oil-source rock

    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Natural Gas GeoscienceAuthor(s): Yao-Ping Wang, Yan-Rong Zou, Jian-Ting Shi, Jun Shi Chemometric methods have unique advantages regarding comprehensive consideration of multiple parameters and the classification of samples or variables. The above is especially suitable for the data mining of a large number of samples, data, as well as the regional oil-oil and oil-source rock correlations. This paper describes the frequently used chemometric methods for geochemical correlations in detail: hierarchical cluster analysis (HCA), principal component analysis (PCA), and the newly introduced method–multidimensional scaling (MDS). MDS and its suitable range, principles, and comparison of each method were also studied. Also, there is a need to discretely treat such issues (i.e., sample screening, correlation parameter, data preprocessing, and the measured distance between samples in high dimensional space) when the chemometric methods are adopted to conduct geochemical correlation in the studied area. These issues are closely related to the reliability of the correlation results.
  • Hydraulic fracture optimization by using a modified Pseudo-3D model in
           multi-layered reservoirs

    • Abstract: Publication date: Available online 1 September 2018Source: Journal of Natural Gas GeoscienceAuthor(s): Garavan Aboozar, Podgornov Valery Mikhaliovich The aim of hydraulic fracturing optimization is to maximize well productivity index by optimizing fracture geometry parameters. Height in geometry calculation is the most important parameter, especially in the multi-layered reservoirs due to the complexity of the in-situ stress distribution. A modified pseudo-3D model suggests a combination of unified fracture design (UFD), 2D fracture propagation models (PKN or KGD) and linear elastic fracture mechanic (LEFM) principle to achieve optimized fracture geometry. First, the LEFM principle has been used to obtain equilibrium fracture height associated with a calculated vertical pressure distribution along the in-situ stress and fracture toughness profiles. Then, the UFD concept in conjunction with 2D fracture models are used to obtain an optimum fracture target length, the corresponding net pressure, and the maximum dimensionless productivity index. This paper shows the insight of the new approach of hydraulic fracture optimization by using an efficient and practical algorithm in calculating equilibrium fracture height growth belong to certain treating pressure. The proposed model is applicable to broad-spectrum of multi-layered oil and gas reservoirs with more accurate estimation of final fracture height and treating pressure. Finally, two case studies have been used to represent that the model is effective and appropriate for practical purposes.
  • Study on the influence of elastic modulus heterogeneity on in-situ stress
           and its damage to gas shale reservoirs

    • Abstract: Publication date: Available online 31 August 2018Source: Journal of Natural Gas GeoscienceAuthor(s): Daobing Wang, Hongkui Ge, Bo Yu, Dongsheng Wen, Jun Zhou, Dongxu Han, Lu Liu Shale heterogeneity has a significant effect on drilling and completions, hydraulic fracturing, as well as hydrocarbon development performance. However, it lacks representation of rock damage/failure caused by the mechanical heterogeneity and “stress shadow” effect during the hydraulic fracturing process. In this paper, the Galerkin finite element method was adopted to numerically simulate the hydro-mechanical coupled interaction based on the solver in the COMSOL Multiphysics software and Matlab scripting development. The Weibull probability density function was used to represent the mechanical heterogeneity of gas shale. Under the condition of fully fluid-solid coupling during the fracking process, the effect of mechanical heterogeneity on von – Mises stress, strain energy density, damage factor, and the fluid pressure was numerically simulated in the gas shale wells. The curves of von – Mises stress, strain energy density, and damage factor along a certain straight line showed the obvious decreasing distribution in a completely homogeneous formation. As the strata are heterogeneously enhanced, their distribution curves showed fluctuations. Moreover, von – Mises stress and strain energy density had a good relationship with damage factors. Accordingly, the method of rock damage/fracture and "stress shadow" effect caused by mechanic heterogeneity was put forward under the circumstance of two–dimensional plane strain. That was to use, the von – Mises stress or strain energy density at the single point or line to characterize the degree of local rupture or the shadow effect of stress, and the average strain energy density per unit area to characterize the degree of rupture of the rock or the intensity of the shadow effect. The study is of great significance to further improve the SRV(Stimulated Reservoir Volume) fracturing design and the productivity of gas shale wells.
  • The role of deep fluid in the formation of organic-rich source

    • Abstract: Publication date: Available online 30 August 2018Source: Journal of Natural Gas GeoscienceAuthor(s): Jiayi Liu, Quanyou Liu, Dongya Zhu, Qingqiang Meng, Wenhui Liu, Dengfeng Qiu, Zhenkai Huang The inner basin has been the focus of organic-rich source rocks -related studies for a long time. In contrast, the effect brought by deep fluids on organic-rich source rocks has not received its much-deserved attention. As a belt connecting the inner and external parts of basins, deep fluids promote the formation of organic-rich source rocks by increasing the marine primary productivity and creating favorable conservation environment. In the productivity facet, deep fluids carry a significant amount of nutrients like NO3−, PO43−, NH4+, hydrothermal gases (i.e., CH4, CO2, H2, and NH3), minor metal elements (i.e., Fe, Mn, Zn, Co, and Cu), as well as microbes from the deep earth like Archaebacteria and thermophilic bacteria. The injection of deep fluids assists organisms to thrive in water and helps facilitate the enhancement of marine primary productivity. The results then create favorable conditions for the formation and enrichment of organic matter. In regards to the organic matter conservation facet, the eruption of deep fluids sends a great deal of CO2 into atmosphere and ocean. By connecting with the Ca2+ and Mg2+ in the water, the CO2 above transforms into carbonate and contribute to the ever increasing water salinity. As a consequence, it will cause the stratification and circulation suspension of the ocean as well as the formation of favorable hydrodynamic conditions and preservation environments. In addition, magma and hydrothermal fluids can also create a reductive environment by sending reductive gases like H2S and CO into the water. In summary, the eruption of deep fluids guarantees the production of essential substances and a favorable environment for the formation and preservation of organic-rich source rocks.
  • Distribution pattern and main factors controlling hydrocarbon accumulation
           of global oil and gas-rich deepwater basins

    • Abstract: Publication date: Available online 1 August 2018Source: Journal of Natural Gas GeoscienceAuthor(s): Hongjun Qu, Gongcheng Zhang, Shuo Chen It is observed from distribution of oil and gas-rich basins as well as summary and analysis of main control factor for hydrocarbon accumulation in global deepwater that oil and gas-rich basins in deepwater in the world shows “one horizontal and two vertical” in distribution pattern and that “one vertical” of deepwater basin group chiefly distributed in Atlantic Ocean from north to south of deepwater oil rich-basin group in the world is under the influence of fault basin group and that deepwater gas-rich basin group along Neo-tethyan tectonic domain and epicontinental basin group in East Africa shows “one horizontal and one vertical” in distribution, being under the influence of “fault basin group in transitional facies”; Comparative analysis and research of main factors for hydrocarbon accumulation in main deepwater oil and gas-rich basins in the world in a systemic way show that main control factors for hydrocarbon accumulation in deepwater oil and gas-rich basin in the world can be reduced to following five types: (1) Reservoir under common control of salt structure, passage system and large turbidite fan; (2) Reservoir under control of source control area and large reservoir body; (3) Reservoir under control of source rock and cap rock control area and large delta; (4) Reservoir under control of source and cover control zone and reef flat; (5) Reservoir under control of source heat control zone, passage system and trap.
  • Discussion on the contribution of graptolite to organic enrichment and
           gas shale reservoir: A case study of the Wufeng–Longmaxi shales in
           South China

    • Abstract: Publication date: Available online 14 July 2018Source: Journal of Natural Gas GeoscienceAuthor(s): Zhen Qiu, Caineng Zou, Xizhe Li, Hongyan Wang, Dazhong Dong, Bin Lu, Shangwen Zhou, Zhensheng Shi, Ziqi Feng, Mengqi Zhang The graptolitic shale of the Wufeng–Longmaxi Formations is widely deposited across the Ordovician and Silurian transition in South China, which is the target of shale gas exploration and development within China. The contribution of graptolites to organic enrichment and reservoir of gas shale is discussed below based on the statistics of nearly 1000 shale samples from the Wufeng Formation and the bottom part of the Longmaxi Formation in the southern and northern margins of the Yangtze plate. The assessment involves graptolites abundance, the total organic carbon (TOC) content analyses, and the different scales of scanning electron microscopy analyses of related samples. The TOC content of the Wufeng–Longmaxi graptolitic shales (including graptolites and non-graptolites, i.e., the host shale) is mainly controlled by that of its host shale, while less affected by the graptolites abundance, indicating that the graptolites barely influence the organic enrichment. Graptolites consist of a large number of organic matter with reticular biological tissue structure; they account for 20%–50% of the graptolitic area. The aforementioned also developed honeycomb-shaped pores with pore sizes ranging 110 nm-1.7 μm (an average of about 500 nm), which are higher than those of the organic pores in the host shale (108–770 nm, average 330 nm), proving that graptolites have an important contribution to shale gas storage space. Since there are a large number of graptolites within the shales from the Wufeng Formation and the bottom part of the Longmaxi Formation, the laminated and stacked local pattern of their distribution provides abundant storage space for shale gas. Moreover, the feature also serves as the predominant channel for shale gas flow. Therefore, the widely developed graptolites should be considered as one of the essential factors controlling enrichment and high productivity of shale gas in the Wufeng–Longmaxi Formations.
  • New approach towards the classification of microporosity in Miocene
           carbonate rocks, Central Luconia, offshore Sarawak, Malaysia

    • Abstract: Publication date: Available online 20 June 2018Source: Journal of Natural Gas GeoscienceAuthor(s): Hammad Tariq Janjuhah, Abubaker Alansari, Deva Prasad Ghosh, Yasir Bashir Microporosity is recognized as a significant concern in limestone reservoirs throughout the world because it presence can highly complicate the hydrocarbon estimation and production. Numerous studies around the globe emphasises on the physical appearance, occurrence, and abundance of microporosity, but no published study has been emphasises on the presence of microporosity in Miocene carbonate reservoirs. Miocene carbonates from Central Luconia, offshore Sarawak, Malaysia, contains a significant amount of micropores, which occurs in grain, matrix, and cement. For a better understanding of the presence of micropores, it is necessary to consider grains, matrix, cement, and pore types. Based on the qualitative and quantitative knowledge of these components a classification of micropores is proposed and their effect on reservoir quality. These results can reduce the number of the assumption made about the internal rock connectivity and quality.For quantitative analysis, 32 high-resolution images of each thin sections were taken under the transmitted light microscopy. Succeeding these 32 images were stacked together as a photo panel to enable quantifying the amount of grain, matrix, cement, pore types and macroporosity using Digital Image Analysis and J.Microvision software. Furthermore, Field Emission Scanning Electron Microscopy images were also used for the measurement of crystallometry of micrite particles, classification of micrite particles and the micropores.Eight facies scheme is introduced based on the detailed lithofacies study of five wells. The qualitative observation of thin sections unveiled that corals, red algae, green algae, foraminifera, echinoderms, sponge, bivalve, and bryozoans are the most dominant components. Foraminifera, red algae, and corals are the far most dominant components covering almost 50% of the total intervals. Regarding porosity types, the mouldic porosity is the far most dominant pore types with converting the total 50% of the interval. Lithofacies observed in these wells indicate a good reservoir quality, but diagenesis plays a vital role in enhancing or reducing their porosity and permeability. Most of the depositional textures of the reservoir are leached, making this location unique to study facies distribution and diagenetic history.Result exhibits that the micrite particles are classified into five classes, which are very fine, fine, medium, coarse and very coarse, with a diameter of 0.1–2 μm, 2–4 μm, 4–6 μm, 6–8 μm and 8–10 μm respectively. The texture and morphology of micrite microtexture are classified into six classes. Among these six classes, rounded, subrounded, trigonal, rhombic (micro-sub)-polyhedral micrite are representing porous micrite particles, whereas fitted bounded subhedral, and fitted fused anhedral are interpreted as tight micrite particles. Furthermore, five micropores classes are introduced based on the size of these particles. The empirical porosity-permeability relationship is affected by the presence of microporosity and its influences the assessment of ultimate recovery of hydrocarbons in Central Luconia, offshore Sarawak, Malaysia.
  • Discovery and geological significance of high quality hydrocarbon source
           rocks in interglacial of Neoproterozoic in the eastern part of the
           southern margin of North China

    • Abstract: Publication date: April 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 2Author(s): Shengfei Qin, Ping Luo, Tongshan Wang, Lanjun Wang, Kui Ma A conglomerate of glacial deposits from Neoproterozoic Sinian is generally developed in the southern margin of the North China Plate. However, whether the hydrocarbon source rock exists in a conglomerate of glacial deposits is still undeterminable as it has not been studied previously. The developmental characteristics of the conglomerate were systematically observed and measured. The conglomerate was subsequently divided into four sets, and the gray-black shale was discovered in between them. The said shale has the thickness of 36 m, 46 m, and 7 m, respectively from top to bottom. The study presents the highly-abundant organic matter in the shale, which belong to the high-quality hydrocarbon source rock. The organic matters are derived from lower organisms. The discovery of thick and high-quality hydrocarbon source rocks in conglomerates opens up new exploration areas for conventional natural gas, as well as provides a powerful basis for shale gas exploration. The dropstones that appeared in hydrocarbon source rocks and conglomerates are cogent evidence of glaciation. The findings provide an important guiding significance for the genesis of the conglomerate.
  • Hydrogen isotopic characteristic of hydrocarbon gas pyrolyzed by
           herbaceous swamp peat in hydrous and anhydrous thermal simulation

    • Abstract: Publication date: April 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 2Author(s): Yi Duan, Yingzhong Wu, Yang Zhao, Xixi Cao, Lanhua Ma In order to understand the influence of diagenetic water medium on hydrogen isotope of thermogenic coalbed gas, the hydrous and anhydrous pyrolytic simulation experiments have been carried out on herbaceous peat. We studied hydrogen isotope composition and its difference and evolution pattern of the pyrolysis hydrocarbon gases It was observed that diagenetic water medium exerts a significant influence on hydrogen isotopic composition of the pyrolysis hydrocarbon gases. The experiment added water with heavier hydrogen isotopic composition than peat-formed environmental water generated hydrocarbon gases with heavier hydrogen isotopic compositions. When peat was subject to continuous pyrolysis until 5.5%Ro, average δD values of the generated methane, ethane and propane were increased by 74‰, 42‰ and 66‰, respectively. It was considered that the reason for hydrous simulation experiment to increase hydrogen isotopic value of pyrolytic hydrocarbon gases is due to isotopic exchange between water-derived hydrogen and organic hydrogen. Mathematical models between the δD values of the hydrocarbon gases generated under the participation of freshwater with higher δD values and Ro values as well as between δD values of the generated hydrocarbon gases were established. These research results provide a scientific basis for the genetic study of thermogenic coalbed methane pyrolyzated by coal-forming materials formed in herbaceous marsh under the participation of diagenetic water media.
  • Study on the optimization of fracturing parameters and interpretation of
           CBM fractured wells

    • Abstract: Publication date: April 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 2Author(s): Qing Feng, Jingping Liu, Zijun Huang, Miao Tian Due to complex seepage mechanism and weak reservoir property, CBM requires being exploited by hydraulic fracturing. In order to comprehend the influencing laws of fracturing parameters' on productivity, recovery efficiency, and well network thoroughly, this paper establishes a non-linear gas-water percolation model of fractured wells. Stress deformations, fluid–structure interaction, CBM desorption, and diffusion research are done. On top of the above, injection pressure-drop well test method is adopted to evaluate fracturing effects. The result demonstrates that the reservoir porosity initially declines and subsequently rises. Permeability is non-linearly affected by threshold pressure gradient. Well space optimization involves fracture orientation, fracture penetration ratio, and fracture conductivity impacts. The rectangle and rhombus well pattern selection refers to reservoir anisotropy critical ratio. The injection pressure-drop test interpretation should be improved further due to the changes in wellbore liquid level. This study is of great significance to improve fracturing evaluation and parameters optimization.
  • The dissolution characteristics of the Chang 8 tight reservoir and its

    • Abstract: Publication date: April 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 2Author(s): Shutong Li, Jingli Yao, Weiwei Mou, Anxiang Luo, Qi Wang, Xiuqin Deng, Meijuan Chu, Yang Li, Cancan Yan The Chang 8 tight reservoir in the area of Jiyuan holds characteristics such as high feldspar content and common feldspar dissolution phenomenon, which are vital to improve the physical properties of tight reservoirs. This paper simulates the interaction between the Chang 8 tight reservoir rock samples and organic acid, analyzes the types and characteristics of dissolution, explains the dissolution mechanism, and quantitatively calculates the influence of dissolution on the porosity of the reservoir on the basis of identifying the fundamental characteristics of the Chang 8 tight reservoir by utilizing the simulation experiment of fluid–rock interaction with high temperature and high pressure combined with polarized microscope and scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis techniques. With the purpose of making the simulation experiment closer to the actual geological conditions, 0.15 mol/L acetic acid solution with pH = 2.65 is used as the reaction fluid, wherein the simulated temperature range is set to 87–103 °C, and the simulated pressure range is set to 24.70–30.18 MPa. The result of the research shows that intergranular pores and feldspar dissolved pores are the primary pore types. The feldspar dissolved pores are more developed and accounts for 39% of the total porosity. The apparent solution ratio is 37.8%–50.0% with a moderate degree of dissolution. Additionally, carbonate minerals can also be dissolved in an acidic condition. The solution ratio of carbonate minerals generally exceeds that of feldspar. The dissolution degree is most robust at about 95 °C, and the burial depth is about 2370–2710 m by the geothermal gradient calculation, which should be the primary distribution area of the favorable tight reservoir of the Chang 8. Overall, dissolution is the main diagenesis type to improve the porosity that can result in the porosity increasing about 3.57%–3.69% in the tight reservoirs of Chang 8. Therefore, it is also the main controlling factor for the development of the "dessert" in the Chang 8 tight reservoir of western Jiyuan area.
  • Main controlling factors and distribution of high-quality deep dolomite
           reservoirs in typical cratonic basins in China

    • Abstract: Publication date: April 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 2Author(s): Jianyong Zhang, Xinfeng Ni, Xingning Wu, Wenzheng Li, Yi Hao, Yanna Chen, Xueju Lü, Mingfeng Gu, Han Tian, Mao Zhu Deep dolomite in cratonic basins is an essential target for future natural gas exploration in China. Statistical analyses of major cratonic basins in China, such as the Sichuan, Tarim, and Ordos basins, indicate that the major types of deep dolomite (including granular dolomite, microbial dolomite, and crystalline dolomite) where fracture-vug and fracture-pore dominate the pore types. It is proposed that the favorable sedimentary microfacies is the base, whereas early dissolution is a necessary condition to form pores. Early dolomitization in penecontemporaneous and shallow burial periods is helpful to preserving the pores that developed during the penecontemporaneous period. Additionally, supergene karstification and structural fractures improve reservoir physical properties. It is pointed that sedimentary facies still control the referred high-quality deep dolomite reservoirs; they inherited more than being transformed in structure. The early sedimentary cycles, rather than depth, control their vertical distribution. Meanwhile, their lateral distribution is controlled by high-energy sedimentary facies belt rather than karstification. It is suggested that future exploration of high-quality deep dolomite reservoirs should target “both sides of an intra-platform rift” and low-middle parts of carbonate slopes.
  • Status and prospects of deep oil and gas resources exploration and
           development onshore China

    • Abstract: Publication date: February 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 1Author(s): Chunchun Xu, Weihong Zou, Yueming Yang, Yong Duan, Yang Shen, Bing Luo, Chao Ni, Xiaodong Fu, Jianyong Zhang Many significant breakthroughs have been made in regards to deep oil and gas exploration and development in recent years. However, a systematic analysis has not been carried out on the progress, challenges, and development trend of exploration and development of onshore deep oil and gas resources in China. This paper summarizes five main points of deep oil and gas resources: (1) more gas, less oil, and complicated phases; (2) high temperature and pressure, as well as profoundly different basins or formations; (3) multiple hydrocarbon sources and accumulations; (4) relatively tight but effective large-scale reservoirs; and (5) complicated accumulation process and multi-stage reconstructions. Based on the exploration and development history of deep oil and gas, this paper points out China's take on it is at the “large-scale discovery stage during which significant achievements have been obtained in carbonate, clastic, and volcanic reservoirs. Nonetheless, there are still four challenges, namely: (1) complex hydrocarbon generation, reservoir evolution, and accumulation restriction on how to determine exploration orientation and targets; (2) long well drilling and completion period, as well as high well construction cost delay petroleum discovery and efficient development; (3) undeveloped logging technology for HPHT slim holes that cannot ensure accurate identification of hydrocarbon reservoir; and (4) effective development and large-scale utilization of unspecific recovery technique and equipment limit. Finally, by the comprehensive analysis, it is concluded that onshore deep oil and gas resources are mainly distributed in three areas of six basins in China. The areas have a vast exploration potential and have strategically successive resources. It is suggested that petroleum companies and universities, as well as research institutes, should work together to overcome difficulties in theory and practical technology for deep oil and gas exploration and development. Such partnership could develop fit-for-purpose theories and technical systems to support deep oil and gas development.
  • Accumulation condition and favorable area evaluation of shale gas from
           the Niutitang Formation in northern Guizhou, South China

    • Abstract: Publication date: February 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 1Author(s): Xianqing Li, Jizhen Zhang, Yuan Wang, Man Guo, Zhe Wang, Feiyu Wang In order to investigate the potential of the Lower Cambrian shale gas in South China, a study on the accumulation condition of shale gas from the Niutitang Formation was conducted. In addition, the favorable accumulation area of shale gas in northern Guizhou was evaluated. The study and evaluation were both analyzed according to the geochemical analysis data of the core and outcrop samples in this paper. The result shows that the Niutitang Formation shale in northern Guizhou is formed in the shallow sea sedimentary environment, which features moderate buried depth (3.0%), type I kerogens, over-mature thermal evolution level (Ro>2.0%), low porosity, abundant micro- and nano-meter pores and fractures, rich brittle mineral (average content>40%), and relatively high gas content (average 1.5 m3/t). The aforementioned feature indicates that the Niutitang Formation in northern Guizhou has good accumulation condition for shale gas. Through the studies above, it is proposed that the southeastern Shiqian—Yuqing—Shibing area is the most favorable area for shale gas accumulation in northern Guizhou.
  • Status and prospects of exploration and exploitation key technologies
           of the deep petroleum resources in onshore China

    • Abstract: Publication date: February 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 1Author(s): Genshun Yao, Xianzhu Wu, Zandong Sun, Chunhao Yu, Yunhua Ge, Xianyou Yang, Long Wen, Chao Ni, Xiaodong Fu, Jianyong Zhang In recent years, China's deep oil and gas exploration and exploitation have developed rapidly. Technological advancements have played an important role in the rapid exploration and highly efficient development. Aimed at the complex engineering geological environment of deep oil and gas in China, this paper has combined the four technological systems that have made significant progress, mainly including: (1) seismic imaging and reservoir prediction techniques for deep–burial complex structures, includign “2W1S” technique (wide-band, wide azimuth, and small bin), RTM (Reverse Time Migration), integrated modeling technology for complex structures and variable velocity mapping technique, improving structural interpretation accuracy, ensuring high precision ofimaging, and prediction for deep geological bodies; (2) deep speed raising and efficiency drilling technology series, which significantly improved the drilling speed, in turn reduced the drilling cost and drilling risk; (3) development of a deep high-temperature and high-pressure logging technology series, which provided a guarantee for the accurate identification of reservoir properties and fluid properties; (4) the efficient development technology for deep reservoirs, especially the development and maturity of the reconstruction volume technology, improve the production of single well and the benefit of deep oil and gas development. This paper further points out the improvement direction of the four major technology series of deep oil based on the analysis of the current development of the four major technological systems. Moreover, the development of applicability and economy for technical system is the key to realize high efficiency and low-cost exploration and development of deep oil and gas.
  • Formation and distribution of large lithologic-stratigraphic oil & gas
           fields (provinces)

    • Abstract: Publication date: February 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 1Author(s): Shizhen Tao, Xuanjun Yuan, Lianhua Hou, Guosheng Zhang, Fan Yang, Xiaowan Tao, Yanzhao Wei, Xin Li, Chenglong Zhang, Lan Wang, Guoxin Sun, Ying Wang, Changhai Gao Since the “Tenth Five-Year Plan”, lithologic and stratigraphic reservoirs have been the main contribution of both the discovery as well as reserve and production increase in China; there were about 80% of proven reserves. The typical reservoirs in six major basins in the eastern, central, and western China were adopted as reservoir forming models. The reservoir forming models in three types of slopes, three types of depressions, and three types of lithologic reservoir assemblages have been built on the basis of application of new technologies, physical modeling of reservoir forming mechanism, and investigation to the formation and distribution of the reservoirs. The evaluation methods for large lithologic reservoirs provinces were established based on the forming mechanism and main controlling factors mentioned above. In addition, the study reveals the main controlling factors and the laws of enrichment of two types of stratigraphic reservoirs (pinch-out and weathered karst reservoirs) based on the evaluation methods for large stratigraphic reservoir provinces that have been established. By comprehensively understanding the laws of enrichment of lithologic-stratigraphic reservoirs in four types of basins, specific evaluation methods and fine exploration techniques have been developed. The findings led to an exploration direction in the “Thirteenth Five-Year Plan” period. The study supported the exploration and selection of oil and gas plays, as well as promoted the exploration of lithologic and stratigraphic reservoirs.
  • Facies and porosity origin of reservoirs: Case studies from the Cambrian
           Longwangmiao Formation of Sichuan Basin, China, and their implications on
           reservoir prediction

    • Abstract: Publication date: February 2018Source: Journal of Natural Gas Geoscience, Volume 3, Issue 1Author(s): Anjiang Shen, Yana Chen, Liyin Pan, Long Wang, Min She The dolostone of the Cambrian Longwangmiao Formation has been a significant gas exploration area in Sichuan Basin. In Gaoshiti-Moxi regions, a giant gas pool with thousands of billion cubic meters' reserve has been discovered. However, the origin of the reservoir and the distribution patterns are still disputed, eventually constraining the dolostone exploration of the Longwangmiao Formation. This paper focuses on the characteristics, origin, and distribution patterns of the dolostone reservoir in the Longwangmiao Formation based on: the outcrop geological survey, cores, thin-sections observation, reservoir geochemical characteristics study, and reservoir simulation experiments. As a result, two realizations were acquired: (1) The Cambrian Longwangmiao Formation could be divided into upper and lower part in Sichuan Basin. Based on the two parts of the Longwangmiao Formation, two lithofacies paleogeographic maps were generated. In addition, the carbonate slope sedimentary models were established. The grainstone shoals are mainly distributed in the shallow slope of the upper part in the Longwangmiao Formation. (2) The grainstone shoals are the developing basis of the dolostone reservoir in the Longwangmiao Formation. Moreover, the contemporaneous dissolution was a critical factor of grainstone shoal reservoir development in the Longwangmiao Formation. Controlled by the exposure surface, the dissolution vugs are not only extensively distributed, but also successively developed along the contemporaneous pore zones. Hence, the distribution patterns could be predicted. The geological understandings of the origin of dolostone reservoir in the Longwangmiao Formation show that the reservoir distributed in the areas of karstification in the Gaoshiti-Moxi regions, as well as the widespread grainstone shoals in the whole basin, are the potential exploration targets.
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