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Natural Resources Research
Journal Prestige (SJR): 0.8  Citation Impact (citeScore): 3 Number of Followers: 7  Hybrid journal (It can contain Open Access articles)ISSN (Print) 1573-8981 - ISSN (Online) 1520-7439 Published by Springer-Verlag  [2468 journals]
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- 3D Static Modeling and CO2 Static Storage Estimation of the
Hydrocarbon-Depleted Charis Reservoir, Bredasdorp Basin, South Africa-
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Abstract: An essential greenhouse gas effect mitigation technology is carbon capture, utilization and storage, with carbon dioxide (CO2) injection into underground geological formations as a core of carbon sequestration. Developing a robust 3D static model of the formation of interest for CO2 storage is paramount to deduce its facies changes and petrophysical properties. This study investigates a depleted oilfield reservoir within the Bredasdorp Basin, offshore South Africa. It is a sandstone reservoir with effective porosity mean of 13.92% and dominant permeability values of 100–560 mD (1 mD = 9.869233 × 10–16 m2). The petrophysical properties are facies controlled, as the southwestern area with siltstone and shale facies has reduced porosity and permeability. The volume of shale model shows that the reservoir is composed of clean sands, and water saturation is 10–90%, hence suitable for CO2 storage based on petrophysical characteristics. Static storage capacity of the reservoir as virgin aquifer and virgin oilfield estimates sequestration of 0.71 Mt (million tons) and 1.62 Mt of CO2, respectively. Sensitivity studies showed reservoir depletion at bubble point pressure increased storage capacity more than twice the depletion at initial reservoir pressure. Reservoir pressure below bubble point with the presence of gas cap also increased storage capacity markedly.
PubDate: 2023-06-01
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- Monitoring Groundwater Storage Based on Satellite Gravimetry and Deep
Learning-
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Abstract: Improper abstraction of groundwater in Iran has led to an average annual subsidence rate of 15 cm/yr. The management of Iran's water resources is essential due to its arid and semiarid climate and traditional agriculture. Monitoring groundwater storage (GWS) changes and their correct interpretation using deep learning (DL) methods can improve our understanding of groundwater systems. For this purpose, in this study, the GWS in Iran from 2003 to 2021 was downscaled using DL based on combining gravity recovery and climate experiment (GRACE) and GRACE-Follow on with a hydrological model. The GWS downscaling was performed from 1° to 0.25°. The GWS in the south of Tehran and northeast of Qazvin had the highest decrease of 15 mm/yr. A new GWS index was developed to correctly interpret the decline in GWS through the standardized precipitation index. The main reason for the decrease in GWS was the development of unsustainable agriculture from 2007 to 2012, which reached its lowest possible level after 2012–2018 with the intensification of climatic conditions. The calculated GWS index correlates more than 80% with 400 piezometric wells in Iran.
PubDate: 2023-06-01
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- Update and Review of Continental Conductive Surface Heat Flow Measurements
in México: An Analysis of Deep Boreholes-
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Abstract: Conductive heat flow is an important parameter that is used to explain, directly or indirectly, several geological, geophysical and geochemical processes in the Earth´s interior. It is also one of the main input parameters for reliable estimations of resources related with geothermal and petroleum systems. That is because heat flow is used to describe subsurface temperature profiles and heat transfer mechanisms, thereby enabling the establishment of heat storage reserves in the case of geothermal systems and conditions of thermal maturation of organic matter in petroleum genesis. Since 2014, collection of data to estimate new continental conductive heat flow values in México has been an exhaustive scientific task. As a result, data from 4159 sites have been compiled, mostly from deep geothermal and petroleum boreholes. In this context, only 3,888 new geothermal gradient data were compiled and used to estimate new heat flow values. These new values complement the 702 continental heat flow values compiled and published between 1974 and 2021. Traditionally, all efforts to measure geothermal gradient in México have focused on the five high enthalpy geothermal fields under exploitation. Therefore, this continuous updating of the continental heat flow database would be an excellent input for Geothermal Play Fairway Analysis, enabling to define areas at a regional level with thermal anomalies and discovering new prospects, resulting in better knowledge of Mexican geothermal resources. Finally, the obtained data will help interested private and public entities to improve the geothermal exploration techniques in collaboration with academic institutions. Moreover, the scientific community interested in Earth science studies will benefit from this information with application to diverse research that involves the thermal evolution of the crust.
PubDate: 2023-06-01
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- Rheology of Coal at Particle Level Characterized by Nanoindentation
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Abstract: Rheological deformation of coal could severely jeopardize the extraction performance during deep coal mining and coalbed methane development by causing instability, shrinkage and collapse of drilling boreholes in the long run. Standard macroscale creep test could only reveal the bulk properties of coal while neglecting the high heterogeneity nature of coal mainly composed of various organic macerals. This study took a low-rank (0.39% Ro) humic coal as research object, and employed nanoindentation technique to study its mechanical and rheological heterogeneity from the particle level. The results showed that mechanical heterogeneity within the humic coal is manifested as inertinite being much harder and less likely to undergo creep than vitrinite. By focusing on vitrinite, both mechanical properties and creep resistance showed negative relationships with loading rate and indentation size. The relationship of creep displacement and time can be best depicted by the model with one spring and two Kelvin–Voigt bodies. To probe into the structure-dependent rheological properties of organic matter in geo-field, carbon stacking structure from X-ray diffraction, creep behavior via nanoindentation and stress distribution simulated by finite-element analysis of coal were compared with another natural carbon aggregation as solid bitumen. The results showed that the coal investigated exhibited a relatively weaker creep resistance than solid bitumen, which is a consequence of its looser stacking manner with small size of crystallites in plane but large layer space inside. The observations here signified the role of chemical structure in determining rheology of organic matter.
PubDate: 2023-06-01
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- A Novel Approach to Three-Dimensional Inference and Modeling of Magma
Conduits with Exploration Data: A Case Study from the Jinchuan Ni–Cu
Sulfide Deposit, NW China-
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Abstract: The genesis of magmatic Ni–Cu–precious metal sulfide ore deposits in open system magma conduits provides a means to reconcile the very large ratios of sulfide to magma in relatively small mafic–ultramafic intrusions. The Jinchuan Intrusion in Gansu Province, NW China, is a classic example where the relationships between the chonoliths and ores can be investigated with extensive exploration data on Ni and Cu concentrations generated during exploration, development, and mining. Along these lines, in this work, a novel approach for inference and modeling of magma conduits with exploration data is proposed. More specifically, for the reconstruction of three-dimensional models (3D) of magma conduits, a Markov random field (MRF) model, which is solved by utilizing a graph cut algorithm (an algorithm for \(n\) -dimensional image segmentation), was developed to find a globally optimal solution, in terms of segmentation of the pattern of magma conduits from the exploration data. In addition, a specialized implicit 3D modeling scheme was devised to generate automatically the underlying 3D geometry of the magma conduits from the solutions of the MRF. The proposed approach was used to establish the 3D architecture of the magma conduit system at Jinchuan, and it illustrated the presence of three different magma conduits. The western intrusion resulted from a bifurcated magma conduit whose entrance was located at the bottom of segment III and its major branch extended sub-horizontally to the southeast of the intrusion. The formation of the eastern intrusion was attributed to two “funnel-shaped” magma conduits whose entrances were located at the bottom of Nos. 1 and 2 orebodies, respectively. The reconstructed magma conduits were supported by evidence from lithological assemblages, grained sizes of olivine, ore-style distributions, and spatial variations of PGE tenors, which reflected the effectiveness and robustness of the proposed approach in 3D inferring and modeling magma conduits. Following the dip direction of the associated magma conduits, the refined locations structurally below orebodies 1, 2, and III-1 were expected to have a high potential for mineral exploration.
PubDate: 2023-06-01
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- Microstructure Evolution of Bituminous Coal Modified by High-Pressure CO2
Foam Fracturing Fluid with Different Treatment Times-
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Abstract: The microstructure of bituminous coal can be changed significantly due to injection of CO2 foam fracturing fluid into the coal seam, affecting CBM production efficiency. To investigate the microstructural change characteristics of bituminous coal treated with high-pressure CO2 foam fracturing fluid at different treatment times (0–24 h), medium-rank bituminous coal was selected as the research object. X-ray diffraction, Fourier transform infrared spectroscopy, and low-temperature N2 adsorption tests were carried out to study the changes in mineral components, functional groups, micropore structure, respectively. It was found that the pore structure of bituminous coal can be changed by CO2 foam fracturing fluid. With increase in modification time, the proportion of macropore (> 50 nm) volume of bituminous coal increased gradually, while the proportion of pore (2–5 nm) volume showed a trend of “increase rapidly–decrease rapidly–decrease slowly.” When the modification time was within 6–24 h, the average pore size showed a quadratic polynomial positive correlation with treatment time, the seepage pore fractal dimension (D1) decreased linearly with increase in modification time, and the adsorption pore fractal dimension (D2) showed the opposite trend. Moreover, with increase in modification time, the infrared peak area of oxygen-containing functional groups and aromatic, aliphatic, and hydroxyl structures of bituminous coal showed a trend of “decrease rapidly–decrease slowly,” the aromaticity and degree of aromatic ring condensation showed “decreasing–increasing–decreasing” trends, and the aliphatic chain length and oxygen-containing functional groups fluctuated and increased. CO2 foam fracturing fluids significantly dissolve clay and carbonate minerals in bituminous coal. Coal microstructure can be changed by CO2 foam fracturing fluid through hydrocarbon extraction and transport, differential swelling, and mineral dissolution. The findings showed that 18–24 h was the optimal time range for fracturing fluid flowback after performing CO2 foam fracturing measurements. The research results are significant for selecting CO2 foam fracturing fluid flowback time and improving CBM recovery.
PubDate: 2023-06-01
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- Elemental Geochemical Distribution of the Jurassic Yan'an Formation in the
Ningdong Coalfield and its Controlling Effect on Coal Reservoir Properties
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Abstract: Geochemical elements are important for judging the coal-forming environments and control on pore structure distribution of coal. Geochemical element and reservoir physical property experiments were carried out on the Jurassic Yan'an Formation coal samples from the Ningdong coalfield. Then, the coal-forming environment of Jurassic Yan'an Formation was distinguished, and the relationship between geochemical elements distribution and pore structure of coals was analyzed. The results indicate that the coal samples have low moisture, low ash, medium volatile matter, and high fixed carbon, with an average Ro of 0.58%, belonging to low-rank coal. The contents of major elements CaO, MgO and Na2O and trace elements Co, Ni, Cu, Zn, Sr, Mo, and Tl were similar to those of Chinese coal, and the other major elements and trace elements were deficient. The contents and distribution pattern of rare earth elements in each sample were similar, and light rare earth elements were relatively enriched. The average porosity of the coal samples was 13.70%, which was dominated by adsorption pores (< 100 nm), and the pore morphology was dominated by parallel plate pore and ink bottle pore. The Yan’an Formation coal in the Ningdong coalfield was formed in a medium-level peat swamp with relative oxidizing conditions, and the sediments were obviously controlled by terrestrial sources. The element distribution indirectly affected the pore characteristics of coal as indicated by changes of provenance and sedimentary environment. The increase of terrigenous input decreased the porosity of the samples and increased the Brunauer–Emmett–Teller (BET) specific surface area (SSA) and the Barrett–Joyner–Halenda (BJH) total pore volume (TPV); the increase of seawater input increased the porosity of the samples and decreases the BET SSA and the BJH TPV. The sedimentary environment changed the provenance and indirectly affected the pore structure of the coal.
PubDate: 2023-06-01
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- Study on Flow Field Variation in Fracture Channel of Coalfield Fire
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Abstract: Coalfield fire areas are widespread in the world, seriously threating the local ecological environment and the economic development. The complexity of occurrence and evolution challenges the scientific prevention and control of coalfield fire. Taking the Tanyaoqu coalfield fire area in China as the object, a physical model was established, and variations of temperature field during coal seam combustion were investigated. Moreover, the distribution of flow field in the fracture channel was examined by numerical simulation. The results indicated that the temperature field in coal seam expands faster in the dip direction than in strike direction, and this is related to the development pattern of fracture channel. The relationship between temperature and time was conformed to the logistic model, while the temperature decreased exponentially with extension of horizontal distance. The temperature variation in rock strata was similar, but lags behind those in the coal seam. Furthermore, at the initiative stage of coalfield fire, both the inflow and outflow happened in the initial fracture. It turned to be the air intake channel when new fractures formed. When the combustion center moved forward, the ventilation quantity decreased until the new fractures formed. Meanwhile, the ventilation quantity increased rapidly when the U-shape channel formed from the interval fractures. The variation of flow field in fracture channel provides a view that the air supply in coalfield fire area changes periodically with the closure and generation of fracture channels, which will influence the evolution of coalfield fire. These are of great significance for revealing the evolution process of coalfield fire.
PubDate: 2023-06-01
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- Detection of Thermal Features Through Interpolation of Well-Log Data in
Low-to-Medium Enthalpy Geothermal System, Gulf of Suez, Egypt-
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Abstract: The Gulf of Suez (GOS) is the most promising geothermal resource for power generation to promote a green energy mix in Egypt. This research clarifies the GOS geothermal features and the control factors forming high-temperature zones by three-dimensional (3D) interpolation of temperature, geothermal gradient, and heat flux borehole temperature data from 281 oil wells with confirmed ranges of 25.1–184.5 °C (average: 105.7 °C), 0.02–6.97 °C/(100 m) (average: 3.1 °C/(100 m)), and 20.4–232.4 mW/m2 (average: 104.2 mW/m2), respectively. K-means clustering distinguished three regional structural areas and two local accommodation zones. These formed the highest potential plays: a medium enthalpy (100–180 °C) basement-dominated play in the southernmost GOS and a low enthalpy (< 100 °C) sediment-dominated play in the northernmost GOS. The results clarified that the GOS resource is characterized by (a) large radiogenic heat and permeability at shallow basement depths, (b) frequent volcanic activity, (c) large porosity and permeability of the clastic and carbonate sequences, (d) development of fractures of varying density, geometry, intersection, and frequent rejuvenation, (e) development of evaporites together with salt diapirs, and (f) frequent earthquakes with magnitudes greater than 3. Strong fault control on the geothermal resource was identified through lineament analysis of integrated bathymetry and topography in the GOS and surrounding area. Findings from the analysis helped to locate efficiently areas with high geothermal potential, leading to better management for binary power generation and enhanced geothermal systems in the GOS.
PubDate: 2023-06-01
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- Experimental Study on Fractal Characteristics of Surface Roughness of
Briquettes and their Effect on Wettability of Coal Samples-
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Abstract: To quantify the influence of surface roughness and its fractal characteristics on the wettability of the samples, coal samples of five particle sizes were selected to produce different cylindrically shaped coal samples in the laboratory, and four grinding methods were used to obtain the coal samples having different roughness values. Three different wetting solutions were utilized to conduct the wetting tests on the coal samples having different roughness values. Theoretical analysis and laboratory studies were carried out to investigate the influence of roughness on wetting parameters. The fractal characteristics of the coal samples with different surface roughness values were analyzed by electron microscopy, and the mechanism of the effect of roughness on wetting performance was analyzed in conjunction with parameters. The results showed that as the surface roughness of the coal samples gradually increased, the fractal dimension increased, the specific surface area of the coal samples increased, the actual contact area of the solid–liquid interface was found to be larger than the apparent contact area, and the adhesion tension and the adhesion work of the wetting solution on the surface of the coal samples increased. The chance of forming a continuous liquid film on the surface of coal samples decreased, more pores were found filled by the wetting solution, resulting in the decrease in contact angle of the liquid on the surface of the coal samples. When the roughness values of the coal samples were in the range of 7–11 μm, the fractal dimension increased rapidly, while the contact angle decreased rapidly.
PubDate: 2023-06-01
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- Variations in Formation Resistivity and Geometric Tortuosity Factors for
Consolidated Niger Delta Formations-
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Abstract: Formation resistivity evaluation is an essential part of electrical properties measurement of porous media. Such deduced properties are often considered in modeling of associated rock properties for better hydrocarbon exploitation. Cognizance of these properties trend are necessary to ensure acceptable magnitudes for regional-based analyses. The aim of this research study was to establish a trend in formation resistivity factor and geometric tortuosity factor for Niger delta formations in Nigeria. These electrical properties were evaluated via core analysis using direct and alternating current sources. Consolidated core samples were procured from different terrains of producing oilfields in Nigeria. Characterized samples in terms of porosities and permeabilities conformed to existing trends. However, clay minerals embedded in acquired samples resulted in lower values of formation resistivity factor. Deduced formation resistivity factors show acceptable values in the range of 3.55–10.26. Geometric tortuosity factor was adopted to evaluate the tortuous nature of Niger delta porous media due to electrical conductivity. Results obtained for geometric tortuosity factors were all < 1. This was used to infer the highly tortuous and sinuous nature of consolidated Niger delta formations. Furthermore, experimental data were subjected to multivariate regression analysis model of second order. All deduced mathematical formulations were comparatively analyzed with existing geometric tortuosity factor models. Mathematical models show reasonable forecast ability for prescribed porosity range with corrected Akaike’s Information Criteria difference of 0.98 and 1.59.
PubDate: 2023-06-01
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- Storage Potential of Multi-State Fluids in Different Lithotypes of
Lignite: An In Situ Water-Gas-Bearing Analysis Based on Nuclear Magnetic
Resonance-
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Abstract: The reservoir properties and gas-bearing characteristics of different lithotypes of lignite are different, resulting in complex migration and accumulation laws of methane in lignite. Following systematic collections of samples of different lithotypes from the Erlian Basin, occurrence modes and storage potential of methane in lignite were explored through a series of isothermal adsorption experiments and NMR-based experiments on original water-containing samples. The maceral composition affects the reservoir characteristics and hydrophilicity of different lithotypes of lignite, which control the reservoir’s gas–water competition. Xylite lignite has a strong adsorption capacity, poor development of macropores, and high irreducible water content. Therefore, among various lithotypes of lignite, xylite lignite has the highest occurrence potential for adsorbed gas and soluble gas and the lowest potential for free gas. Notably, the soluble gas in lignite is never dominant in the gas composition. Therefore, gas in xylite lignite is mainly adsorbed. Due to carbonization, the fusain-rich lignite retains many unexpanded primary plant tissue structures and has developed macropore spaces and weak hydrophilicity. Therefore, the fusain-rich lignite has high free fluid porosity and the highest free gas storage potential. When the burial depth of the matrix lignite is less than 500 m, the methane is mainly adsorbed. The storage potential of free gas gradually exceeds that of adsorbed gas as the burial depth increases. There are apparent differences in the occurrence states and accumulation patterns of methane in different lithotypes of lignite. Clarifying methane’s occurrence and storage potential in different lithotypes of lignite are significant for evaluating methane resources and exploring the methane enrichment model.
PubDate: 2023-06-01
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- Modified Method for Calculating Saturation Gas Content in Deep Coal and
the Pore Size Effect of Methane Adsorption on Guizhou Middle- and
High-Rank Coals-
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Abstract: Comprehensive development of deep coalbed methane is the basis of sustainable coalbed methane development in China. An accurate assessment of deep coal gas-bearing characteristics is of great significance for the efficient development of coalbed methane. The Guizhou middle- and high-rank coals were taken as examples. The quantitative characterization of full pore size distribution and isothermal adsorption experiments were first conducted. Then, the calculation of saturated gas content in deep coal was modified, and various methane adsorptions in middle- and high-rank coal were elaborated. The difference in saturated gas content calculated by two methods and their pore size effect was then discussed. The results showed that (1) the absolute adsorption amounts of WJZ-11 and LT-6 coals have different increases as a function of depth. The gap between the excess adsorption and absolute adsorption amount showed a positive relationship with depth. (2) Adsorbed gas is still the main constituent of saturated gas content in deep coal. The difference calculated by the two methods showed significant increase in depth, similar to high-rank coal below 2000 m. The relative size between micropore volume and adsorption space determines this difference. (3) The average number of layers of the adsorbed molecule (ANLAM) ranged from 1.25 to 1.66 in WJZ-11 coal, indicating the coexistence of micropore filling and multilayer adsorption. The ANLAM ranged from 0.45 to 0.56 in LT-6 coal, suggesting unsaturated monolayer adsorption with minor volume filling in smaller micropores. (4) The pore size effect of methane adsorption as a function of depth is the fundamental reason for the different calculated results of saturated gas content in deep coal. However, it shows different effects on middle- and high-rank coals. This study aimed to provide a new idea and method for distinguishing methane adsorption behaviors of middle- and high-rank coals and their applicability for prediction of saturation gas content in deep coal.
PubDate: 2023-06-01
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- Exploring Chromium Ore Consumption: New Perspectives from Hybrid
CEEMDAN–S-Curve Modeling-
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Abstract: Chromium ore is an important metallic raw material that is widely used in the metallurgy industry, chemical industry, and refractory. Clarifying the consumption mechanism of chromium ore is crucial for policy making, enterprise production, and commodity investment. Based on the signal decomposition tool and S-curve model, a new hybrid complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN)–S-curve model is proposed to analyze chromium ore consumption of different countries for the last 100 years. The results showed the following. (1) Per capita chromium ore consumption can be decomposed into low-frequency, medium-frequency, and high-frequency components, which contribute more than 55%, 10–30%, and less than 15%, respectively, to the volatility of the original series. These can be interpreted as economic development represented by GDP per capita, shocks induced by significant events, and normal market disequilibrium, respectively. (2) The CEEMDAN–S-curve facilitates understanding and data logic of data by linking consumption to end-use segments. (3) A new strategy is provided to analyze the consumption mechanism of other commodities for future modelers. Moreover, based on the results, a series of topics related to chromium ore consumption are discussed, such as resource recovery, environmental pollution, CO2 emissions, and consumption trends. The discussions emphasize that, to reach sustainable development goals, a series of measures should be implemented, such as developing advanced smelting technology, recycling technology, and effective enforcement measures.
PubDate: 2023-04-16
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- ConvLSTM for Predicting Short-Term Spatiotemporal Distribution of Seismic
Risk Induced by Large-Scale Coal Mining-
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Abstract: Coal-burst is a typical dynamic disaster that raises mining costs, diminishes mine productivity, and threatens workforce safety. To improve the accuracy of coal-burst risk prediction, deep learning is being applied as an emerging statistical method. Current research has focused mainly on the prediction of the intensity of risks, ignoring their evolution in a spatiotemporal distribution. A spatial distribution model based on the seismic energy attenuation law was established to describe quantitatively the relative spatial evolution of seismic risk at the work face. Spatiotemporal sequence samples were constructed using seismic events that occurred during the extraction of LW250105 in Huating Coal Mine. A deep learning model based on a convolutional long short-term memory network (ConvLSTM) was constructed to predict the short-term spatiotemporal distribution of seismic risks. A new loss function and metric were used in the deep learning model to improve its performance. The results showed that (1) the optimal performance of the ConvLSTM model improved on the test set by 14.7%, compared with the baseline; (2) the prediction results of the ConvLSTM model were a correction of the current RSR distribution; and (3) the multistep prediction results outperformed the baseline, with improvement rates ranging from 20 to 27%. The effectiveness of the ConvLSTM model in predicting the spatiotemporal evolution of seismic risk was demonstrated by comparing the predicted distribution in several cases. The proposed method can explicate the evolution and distributions of the key characteristics associated with seismic risk and provide effective guidance for the early warning of coal-bursts.
PubDate: 2023-04-14
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- Seismic Data Integration Workflow in Pluri-Gaussian Simulation:
Application to a Heterogeneous Carbonate Reservoir in Southwestern Iran-
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Abstract: In this study, we present a procedure for reservoir property modeling in a channelized carbonate reservoir based on hierarchical geostatistical simulation and seismic data integration. Because soft data integration in facies modeling has always been challenging, we used an innovative approach to incorporate seismic data in facies simulations properly. In this regard, we produced a facies proportion model (FPM) using sequential Gaussian co-simulation of facies proportion as primary data and acoustic impedance as secondary data. The facies proportions were extracted from vertical proportion curves, and the impact of seismic data in facies simulation was determined with the help of correlation coefficient maps. An alternative type of seismic-based soft data was also derived using a supervised neural network to create a facies probability cube (FPC) for each facies. Afterward, pluri-Gaussian simulation (PGS) was implemented to these two prepared soft datasets, and consequently, porosity was simulated twice in each of the models—with and without seismic-derived secondary data. Histogram analysis showed that the facies modeled with the PGS–FPM method reproduced the original well data better than the PGS–FPC method. In addition, blind wells validation showed that the PGS–FPM outputs had up to 79% accuracy, while channel geometries were better constructed using the PGS–FPC approach. The difference between the reservoir quality of channel and background was distinguishable in all hierarchical simulated porosity results. At the same time, the predicted results from simulated porosity in PGS–FPM facies had stronger correlation with true values in blind wells.
PubDate: 2023-04-05
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- Methane Adsorption Characteristics Under In Situ Reservoir Conditions of
the Wufeng–Longmaxi Shale in Southern Sichuan Basin, China: Implications
for Gas Content Evaluation-
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Abstract: The accuracy of adsorbed gas content under actual in situ reservoir conditions is crucial for the evaluation of shale gas reserves. In this study, the characteristics of methane adsorption on the Wufeng–Longmaxi shale were investigated under a wide range of pressure (0–51 MPa) and actual in situ water saturation. Methane–shale adsorption exhibits the Gibbs excess adsorption phenomenon at high pressure. The excess adsorption amount needs be corrected to absolute adsorption amount, otherwise it will be seriously underestimated. The optimal supercritical methane adsorption model was determined by the corrected Akaike’s Information Criterion method. The methane adsorption amount of shale samples ranged from 1.521 to 4.079 m3/t. Adsorption capacity was dominated by the total organic carbon content as well as micropore volume and total specific surface area. Additionally, pore volume and specific surface area were contributed mainly by abundant micropores associated with organic matter. Thermodynamic parameters revealed that the adsorption of methane on shale was an exothermic process. As the temperature increased from 40 to 80 °C, the methane adsorption capacity decreased from 4.27 to 2.99 m3/t, a 30% decrease. The actual in situ water saturation correlated primarily with clay content, regardless of clay types, and increased with clay content. The formation of an adsorbed water film and the blockage of pores for gas adsorption by clusters of water molecules significantly lowered the adsorption capacity. The relative difference in the adsorption capacity increased with water saturation, with the adsorption capacity of water-bearing shales decreasing by 21–84% at a water saturation of 30–71% compared to dry shales.
PubDate: 2023-04-03
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- Experimental Study on the Damage Evolution Behavior of Coal Under Dynamic
Brazilian Splitting Tests Based on the Split Hopkinson Pressure Bar and
the Digital Image Correlation-
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Abstract: Fully understanding the dynamic tensile behavior of coal is of great significance to the prevention and control of rock burst in underground coal resource mining. In this study, the split Hopkinson pressure bar and the digital image correlation were used to conduct dynamic Brazilian splitting experiments on coal to explore its dynamic tensile behavior. The evolution behaviors of vertical displacement, displacement velocity, and displacement acceleration fields in the process of dynamic tensile fracture of coal were investigated; the damage process of coal was characterized quantitatively; and the relationship between damage and energy was analyzed. The results showed that absolute values of displacement, displacement velocity, and displacement acceleration gradually expand along the central axis to the upper and lower ends of coal. The displacement changed in the form of variable velocity and acceleration, proving that the damage of coal evolves in the form of variable velocity and acceleration. The damage acceleration reached the maximum soonest, followed by the damage velocity, and the degree of damage was last. Before the peak stress, the absorbed energy can only cause slight damage to the coal but it led to high damage velocity and acceleration. After the peak stress, a little added absorbed energy can lead to more severe damage to the coal, with high damage velocity and low damage acceleration. Although the strength, energy, displacement, displacement velocity, and displacement acceleration of coal at different impact velocities were different, their forms of evolution and damage modes were similar.
PubDate: 2023-04-02
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- Prediction of Thermal Coal Ash Behavior of South African Coals:
Comparative Applications of ANN, GPR, and SVR-
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Abstract: The coal ash fusion characteristics are a significant factor to consider while designing a boiler to match a coal or different coal range. Characterization of coal ash provides the fundamental mechanism that controls the heating efficiency of the coal in a pulverized coal-fired boiler, regarding the coal minerals association. Changes in coal properties could lead to changes in ash properties, i.e., ash fusion temperatures (AFT) and ash elemental composition, which could lead to slagging or fouling issues inside the boiler. The main cause could be attributed to the high temperature of the combustion process and the low melting point of ash, or vice versa. This study aimed to develop AFT prediction models using coal samples from different coalfields to predict the initial deformation temperature (DT), softening temperature (ST), hemispherical temperature (HT) and fluid temperature (FT) of coal ash. The artificial neural network (ANN), Gaussian process regression (GPR) and support vector regression (SVR) are the three machine learning tools used in this modeling. The resulting AFT predictive models indicated that the ANN model predicted DT, ST, HT and FT more adequately and reliably than the GPR and SVR. The Taylor’s diagram, which enabled easy identification of the closeness of the model predictions to the measured data, also indicated that the ANN outperformed all the other models.
PubDate: 2023-04-02
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- Spectral Decomposition-Based Quantitative Inverted Velocity Dynamical
Simulations of Early Cretaceous Shaly-Sandstone Natural Gas System, Indus
Basin, Pakistan: Implications for Low-Velocity Anomalous Zones for Gas
Exploration-
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Abstract: Incised marine valleys (ISVs) form brilliant petroleum systems. The development of an ISV occurs throughout a rapidly falling sea, followed by a subsequent rise (transgressive system), which fills the ISV with coarse-grained reservoir facies. These reservoir facies have variable velocities, thicknesses, and lateral continuity, which are not predictable using bandlimited seismic amplitude. This study used a new technique for imaging the heterogeneous depositional systems of the early Cretaceous Middle Indus Basin of Pakistan. This technique uses amplitude-based inverted velocity simulations (SIVS) to quantify the ISVs. The conventional amplitudes can predict the 31-m-thickest sandstone-filled ISVs with a laterally continuous distance of 9 km. The 18-Hz waveform-based SIVS predicted the 8.2 m thick reservoir facies of channelized sandstone with a laterally continuous distance of 2 km. The SIVS predicted the tuning effects due to destructive interference of the down-going seismic waves along the erosional zones of the channel system, which have simulated velocities of 3674 to 5237 m/s. The SIVS simulated the actual velocities of the seismic waves of Pakistan’s Indus natural gas systems with a deposition of 8 to 8.2 m thick sandstone-filled channels and velocities of 2960 to 2992 m/s. This work has strong implications for achieving enhanced thickness of sedimentary reservoirs inside ISVs, which can be used for exploring any shoreline petroleum system with similar geology and structure.
PubDate: 2023-04-01
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