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19 pages, 16298 KiB

Open AccessArticle

Natural Maturation-Induced Changes in Molecular Structure and Associated Micropores of Kerogen in Shale: Implications for Geological Storage of Carbon Dioxide

by Yuewen Zhu, Fuhua Shang, Yulong Zhao, Guanqun Zhou, Yutong Pang, Ke Miao and Yujin Chen

Processes 2025, 13(4), 1150; https://doi.org/10.3390/pr13041150 - 10 Apr 2025

Viewed by 284

Abstract

Kerogen micropores in shale are crucial for gas sorption; nevertheless, their formation and evolution have been insufficiently studied. To qualitatively and quantitatively analyze changes in the molecular structure and associated micropores of kerogen throughout natural maturation, a series of experiments were performed on [...] Read more.

Kerogen micropores in shale are crucial for gas sorption; nevertheless, their formation and evolution have been insufficiently studied. To qualitatively and quantitatively analyze changes in the molecular structure and associated micropores of kerogen throughout natural maturation, a series of experiments were performed on collected kerogen samples with varying maturity levels. The results demonstrated that the evolution of the chemical structure and associated micropores of kerogen can be divided into three stages during thermal evolution. When Ro < 1.43%, micropores are primarily controlled by the aliphatic composition of kerogen, resulting in a reduction in the micropore volume with decreasing numbers of aliphatic functional groups. When 1.43% < Ro < 1.93%, the micropore structure is primarily governed by the aromatic composition of kerogen and the micropore volume exhibits a gradual increment with increasing aromatic ring size. When Ro > 1.93%, the micropore volume rapidly increases with increasing aromatic composition of kerogen, and the aromatic rings become more orderly. Moreover, molecular simulations also show that the adsorption curves of CO₂ and CH₄ are type I isotherms, and that the adsorption capacity of CO₂ is greater than that of CH₄ under the same conditions, which indicates that the microscopic adsorption mechanism of CH₄ and CO₂ is gas competitive adsorption. This research offers new perspectives on the formation and evolution of kerogen micropores, and the carbon sequestration process. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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18 pages, 6145 KiB

Open AccessArticle

Classification and Analysis of Dominant Lithofacies of the Fengcheng Formation Shale Oil Reservoirs in the Mahu Sag, Junggar Basin, NW China

by An Xie, Heyuan Wu, Yong Tang, Wenjun He, Jingzhou Zhao, Weitao Wu, Jun Li, Yubin Bai and Liang Yue

Processes 2025, 13(4), 1065; https://doi.org/10.3390/pr13041065 - 2 Apr 2025

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Abstract

The exploration of the Fengcheng Formation has revealed the characteristic orderly coexistence of conventional reservoirs, tight reservoirs, and shale reservoirs, constituting a full spectrum of reservoir types, and is important for unconventional oil and gas exploration and development. Affected by frequent volcanic tectonic [...] Read more.

The exploration of the Fengcheng Formation has revealed the characteristic orderly coexistence of conventional reservoirs, tight reservoirs, and shale reservoirs, constituting a full spectrum of reservoir types, and is important for unconventional oil and gas exploration and development. Affected by frequent volcanic tectonic movement, hot and dry paleoclimate, and the close provenance supply distance, unique saline–alkaline lacustrine deposits formed during the depositional period of the Fengcheng Formation. The lithologies of the Fengcheng Formation are highly diverse, with endogenous rocks, volcanic rocks, terrigenous debris, and mixed rocks overlapping and forming vertical reservoir changes ranging from meters to centimeters. Owing to the complexity of rock types and scarcity of rock samples, the evaluation of reservoirs in mixed-rock has progressed slowly. Hence, we aimed to evaluate the characteristics of Fengcheng Formation shale oil reservoirs. Centimeter-level core characteristics were analyzed based on the lithological change and structural characteristics. To investigate the lithofacies of the Fengcheng Formation in the Mahu Sag and factors affecting reservoir development, high-frequency sedimentary structures were analyzed using sub-bio-buffering electron microscopy, energy spectrum testing, and fluorescence analysis. The results showed that the shale oil reservoirs in the study area can be divided into four categories: glutenite, volcanic rock, mixed rock, and endogenous rock. The reservoir capacity has improved and can be divided into eight subcategories. Mixed-rock reservoirs can be further divided into four subcategories based on differences in structure and composition. Differences in the bedding and dolomite content are the main factors controlling the differences in the physical properties of this type of reservoir. This study provides a reference for the classification and characteristic study of shale oil reservoirs in saline–alkali lake basins. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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20 pages, 4189 KiB

Open AccessArticle

Prediction of Influencing Factors on Estimated Ultimate Recovery of Deep Coalbed Methane: A Case Study of the Daning–Jixian Block

by Feng Wang, Mansheng Wu, Yuan Wang, Wei Sun, Guohui Chen, Yanqing Feng, Xiaosong Shi, Zengping Zhao, Ying Liu and Shuangfang Lu

Processes 2025, 13(1), 31; https://doi.org/10.3390/pr13010031 - 26 Dec 2024

Viewed by 583

Abstract

China has vast amounts of deep coalbed methane resources but is still in the early stage of deep coalbed methane development; thus, it lacks mature gas exploitation and development theories and technologies, particularly effective methods for evaluating final recoverable reserves. This paper intends [...] Read more.

China has vast amounts of deep coalbed methane resources but is still in the early stage of deep coalbed methane development; thus, it lacks mature gas exploitation and development theories and technologies, particularly effective methods for evaluating final recoverable reserves. This paper intends to develop a method that can rapidly and accurately predict deep coalbed methane EUR before well spacing to guide the formulation of rational exploitation schemes and full exploitation of geological resources, thus lowering costs and enhancing efficiency. Taking deep coalbed methane in the Daning–Jixian block of the Ordos Basin as the research object, this paper first uses the production decline method to evaluate the EUR of brought-in wells and analyzes the influence of geological conditions and engineering parameters on the EUR. Second, the ADASYN method is used to process the unevenly distributed samples to solve the small number and poor representativeness of the machine learning model samples. After this, the BP neural network, support vector machine, and Gaussian process regression are used to build EUR evaluation models, and the models are compared and the best is selected. Lastly, the selected EUR evaluation model is applied to analyze the influence weights of geological conditions and engineering parameters on EUR. According to the research results, the MAPEs of the BP neural network, support vector machine, and Gaussian process regression models reach 7.03%, 7.23%, and 1.28%, respectively, after ADASYNA oversampling. However, the Gaussian process regression model may bear the risk of overfitting. The model comparison results show that the support vector machine model is superior to the BP neural network model and the Gaussian process regression model. Therefore, the support vector machine is favorably selected to predict EUR in this paper. Feature importance analysis results indicate that engineering parameters (including clusters, horizontal length, fracturing liquid, and proppant) are the major factors influencing the EUR prediction results. This paper establishes a model for predicting the EUR of deep coalbed methane, which provides a reference for the future formulation of well spacing schemes in the surveyed region. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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19 pages, 17295 KiB

Open AccessArticle

Gas Charging Characteristics and Controlling Factors in Tight Sandstone Reservoir of Xujiahe Formation, Sichuan Basin

by Zengye Xie, Yurun Rui, Jianying Guo, Jian Li, Rongjun Yang, Du Guo and Shuangbiao Han

Processes 2024, 12(12), 2878; https://doi.org/10.3390/pr12122878 - 16 Dec 2024

Viewed by 703

Abstract

The tight reservoirs in the Sichuan Basin generally contain water and have complex gas–water relationships. The dynamic changes and main controlling factors of natural gas injection are unclear, which has had a serious impact on the exploration and development of tight sandstone gas. [...] Read more.

The tight reservoirs in the Sichuan Basin generally contain water and have complex gas–water relationships. The dynamic changes and main controlling factors of natural gas injection are unclear, which has had a serious impact on the exploration and development of tight sandstone gas. This article selects samples from Yongqian and Qiulin gas fields to characterize the reservoir characteristics of the tight sandstone samples in the Xu-3 section. Nuclear magnetic resonance technology is applied to plan gas–water injection simulation experiments, and the dynamic changes in pore water and gas content during the natural gas injection of tight reservoir rock samples are characterized. The main controlling factors are analyzed based on the theory of nuclear magnetic resonance singlet and multifractal models. The results showed that material composition, pore type, structural characteristics, and physical properties cooperatively control the charging characteristics of natural gas. There was no significant difference in mineral content among the tight sandstone samples, and the pore morphology types were mainly parallel plate-like pores and fracture-type pores. There were significant differences in the pore structure characteristics of the samples with varying burial depths. The heterogeneity of gas-bearing pores is negatively related to the buried depth of tight sandstone, is a coupling relationship with quartz and feldspar content, and is negatively correlated with pore permeability. The stronger the sample heterogeneity, the more unfavorable it is for natural gas migration and accumulation. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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23 pages, 8705 KiB

Open AccessArticle

Multiscale Qualitative–Quantitative Characterization of the Pore Structure in Coal-Bearing Reservoirs of the Yan’an Formation in the Longdong Area, Ordos Basin

by Rong Wang, Baohong Shi, Tao Wang, Jiahao Lin, Bo Li, Sitong Fan and Jiahui Liu

Processes 2024, 12(12), 2787; https://doi.org/10.3390/pr12122787 - 6 Dec 2024

Viewed by 855

Abstract

Accurate characterization of coal reservoir micro- and nanopores is crucial in evaluating coalbed methane storage and gas production capacity. In this work, 12 coal-bearing rock samples from the Jurassic Yan’an Formation, Longdong area, Ordos Basin were taken as research objects, and micro- and [...] Read more.

Accurate characterization of coal reservoir micro- and nanopores is crucial in evaluating coalbed methane storage and gas production capacity. In this work, 12 coal-bearing rock samples from the Jurassic Yan’an Formation, Longdong area, Ordos Basin were taken as research objects, and micro- and nanopore structures were characterized via scanning electron microscopy, high-pressure mercury pressure, low-temperature N₂ adsorption and low-pressure CO₂ adsorption experiments. The main factors controlling coal pore structure development and the influence of pore development on the gas content were studied by combining the reflectivity of specular samples from the research area, the pore microscopic composition and the pore gas content determined through industrial analyses and isothermal absorption experiments. The results show that the coal strata of the Yan’an coal mine are a very important gas source, and that the coal strata of the Yan’an Formation in the study area exhibit remarkable organic and clay mineral pore development accompanied by clear microfractures and clay mineral interlayer joints, which together optimize the coal gas storage conditions and form efficient microseepage pathways for gas. Coalstone, carbonaceous mudstone and mudstone show differential distributions in pore volume and specific surface area. The general trend is that coal rock is the best, carbonaceous mudstone is the second best, and mudstone is the weakest. The coal samples’ microporous properties are positively correlated with the coal sample composition for the specular group, whereas there is no clear correlation for the inert group. An increase in the moisture content of the air-dried matrix promotes adsorption pore development, leading to increases in the microporous volume and specific surface area. CH₄ adsorption in coal rock increases with increasing pressure, and the average maximum adsorption is approximately 8.13 m³/t. The limit of the amount of methane adsorbed by the coal samples, V_L, is positively correlated with the pore volume and specific surface area, indicating that the larger the pore volume is, the greater the amount of gas that can be adsorbed by the coal samples, and the larger the specific surface area is, the greater the amount of methane that can be adsorbed by the coal samples. The P_L value, pore volume and specific surface area are not correlated, indicating that there is no direct mathematical relationship between them. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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18 pages, 5575 KiB

Open AccessArticle

Investigation of Coal Structure and Its Differential Pore–Fracture Response Mechanisms in the Changning Block

by Xuefeng Yang, Shengxian Zhao, Xin Chen, Jian Zhang, Bo Li, Jieming Ding, Ning Zhu, Rui Fang, Hairuo Zhang, Xinyu Yang and Zhixuan Wang

Processes 2024, 12(12), 2784; https://doi.org/10.3390/pr12122784 - 6 Dec 2024

Viewed by 702

Abstract

The deep coal seams in the southern Sichuan region contain abundant coalbed methane resources. Determining the characteristics and distribution patterns of coal structures in this study area, and analyzing their impact on pore and fracture structures within coal reservoirs, holds substantial theoretical and [...] Read more.

The deep coal seams in the southern Sichuan region contain abundant coalbed methane resources. Determining the characteristics and distribution patterns of coal structures in this study area, and analyzing their impact on pore and fracture structures within coal reservoirs, holds substantial theoretical and practical significance for advancing coal structure characterization methods and the efficient development of deep coalbed methane resources. This paper quantitatively characterizes coal structures through coal core observations utilizing the Geological Strength Index (GSI) and integrates logging responses from different coal structures to develop a quantitative coal structure characterization model based on logging curves. This model predicts the spatial distribution of coal structures, while nitrogen adsorption data are used to analyze the development of pores and fractures in different coal structures, providing a quantitative theoretical basis for accurately characterizing deep coal seam features. Results indicate that density, gamma, acoustic, and caliper logging are particularly sensitive to coal structure variations and that performing multiple linear regression on logging data significantly enhances the accuracy of coal structure identification. According to the model proposed in this paper, primary-fragmented structures dominate the main coal seams in the study area, followed by fragmented structures. Micropores and small pores predominantly contribute to the volume and specific surface area of the coal samples, with both pore volume and specific surface area increasing alongside the degree of coal fragmentation. Additionally, the fragmentation of coal structures generates more micropores, enhancing pore volume and suggesting that tectonic coal has a greater adsorption capacity. This study combines theoretical analysis with experimental findings to construct a coal structure characterization model for deep coal seams, refining the limitations of logging techniques in accurately representing deep coal structures. This research provides theoretical and practical value for coal seam drilling, fracturing, and reservoir evaluation in the southern Sichuan region. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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17 pages, 14375 KiB

Open AccessArticle

Numerical Simulation of Coal’s Mechanical Properties and Fracture Process Under Uniaxial Compression: Dual Effects of Bedding Angle and Loading Rate

by Jianchun Ou, Jizhan Niu, Bican Wang, Wei Zhang, Jing Zhao, Benming Lyu, Beihuai Zhan and Yue Ma

Processes 2024, 12(12), 2661; https://doi.org/10.3390/pr12122661 - 25 Nov 2024

Viewed by 722

Abstract

In view of the significant influence of bedding structure on the mechanical characteristics and fracture behavior of coal, uniaxial compression discrete element numerical simulation experiments were carried out on coal samples with bedding angles of 0°, 30°, 60°, and 90°, and loading rates [...] Read more.

In view of the significant influence of bedding structure on the mechanical characteristics and fracture behavior of coal, uniaxial compression discrete element numerical simulation experiments were carried out on coal samples with bedding angles of 0°, 30°, 60°, and 90°, and loading rates of 10⁻³/s, 10⁻²/s, 10⁻¹/s, and 10⁰/s, respectively, using PFC 6.0 software. The dual effects of bedding angle and loading rate on the mechanical properties of coal and its damage behavior were analyzed. The results show that (1) as the loading rate increases, the peak strength of the specimen increases, and the damage intensifies. The counts of the three types of cracks increased exponentially, while the crack growth rate was dramatic. (2) With the increase in loading rate, the density of the compressive stress force chain inside the specimen increases and gathers to the two ends, and the density of the tensile stress force chain is basically unchanged but gathers to the middle. The overall strength of the force chain changes according to the law of decreasing and then increasing. (3) With the increase in the bedding angle, the peak strength decreases and then increases, and the curve is approximately “V” shape. When the bedding angle is 60° and 90°, the peak stress is minimum and maximum, respectively. Shear cracks are dominant in the model, and the crack distribution shows a trend of increasing and then decreasing. (4) With the increase in the bedding angle, the density of the compressive stress force chain gradually decreases, and the density of the tensile stress force chain appears to be aggregated. The overall strength of the force chain changes according to the law of decreasing and then increasing. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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14 pages, 11316 KiB

Open AccessArticle

The Gas Generation Process and Modeling of the Source Rock from the Yacheng Formation in the Yanan Depression, South China Sea

by Liu Yang, Gaoyuan Yan, Yang Wang, Yaoning Liu, Xiujie Chen, Tang Pan and Hanyu Zhang

Processes 2024, 12(11), 2476; https://doi.org/10.3390/pr12112476 - 7 Nov 2024

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Abstract

The research on deepwater oil and gas exploration areas is relatively limited, and sample collection is difficult. A drilled coal sample from Yanan Depression was used to investigate the hydrocarbon generation process, and the potential, by a gold tube thermal simulation experiment. The [...] Read more.

The research on deepwater oil and gas exploration areas is relatively limited, and sample collection is difficult. A drilled coal sample from Yanan Depression was used to investigate the hydrocarbon generation process, and the potential, by a gold tube thermal simulation experiment. The results show that the total gas yield was much higher than the oil yield. According to an analysis of the gas pyrolysis data, as represented by ln(C₁/C₂) and ln(C₂/C₃), the gas generation process consisted of two forms, namely, primary gas with ~1.33% Ro and secondary gas that occurred at levels greater than 1.33% Ro. The primary gas from kerogen was generated at ~1.33% Ro, which coincided with the %Ro value of the maximum oil yield. The activation energy distribution of the C₁–C₅ generation processes ranged from 54 to 72 kcal/mol, with a frequency factor of 6.686 × 10¹⁴ s⁻¹ for the coal sample. We constructed the history of gas generation on the basis of the process and kinetic parameters, combined with data on the sedimentary burial and thermal history. The extrapolation of the gas history revealed that the gas has been generated from 5 Ma to the present, with a maximum yield of 178.5 mg/gTOC. This history suggests that the coal has good primary gas generation potential and provides favorable gas source conditions for the formation of gas fields. This study provides a favorable basis for expanding the effective source rock areas. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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19 pages, 2330 KiB

Open AccessArticle

Investigation into the Geological Origin and Influencing Factors of Selenium-Enriched Soil in Licheng, Jinan, Shandong Province

by Jie Li, Naishuang Bi, Yanling Cao, Haishun Yin, Pinrui Qin, Lian Liu, Bo Wu, Lijie Jin, Mingyang Tian, Zhixiang Niu and Baoju Zhao

Processes 2024, 12(11), 2461; https://doi.org/10.3390/pr12112461 - 6 Nov 2024

Viewed by 1262

Abstract

The geochemical classification of soils is crucial for the scientific development and utilization of land, particularly in the investigation of selenium-rich soils, which plays a guiding role in the cultivation layout of local selenium-rich agricultural products. This study involves the collection and analysis [...] Read more.

The geochemical classification of soils is crucial for the scientific development and utilization of land, particularly in the investigation of selenium-rich soils, which plays a guiding role in the cultivation layout of local selenium-rich agricultural products. This study involves the collection and analysis of over 6000 samples of soil, water quality, and crops from the entire area of Licheng District in Jinan City, Shandong Province. By analyzing the data in conjunction with the geochemical classification standards for soil nutrient levels, soil environmental geochemical levels, and comprehensive soil quality geochemical levels, we delineated a distribution area of selenium-rich soils covering 192.26 km² in Licheng District, providing a bibliographic basis for the scientific planning of agriculture and forestry in the region. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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22 pages, 35187 KiB

Open AccessArticle

Sedimentary Environment and Organic Matter Accumulation of Continental Shales in Xiahuayuan Formation in Xuanlong Depression, Yanshan Area

by Wei Jiang, Yang Hu and Peng Wu

Processes 2024, 12(11), 2436; https://doi.org/10.3390/pr12112436 - 4 Nov 2024

Viewed by 921

Abstract

The shale sedimentary environment is crucial for evaluating shale gas reservoirs and sweet spot zones. The Xiahuayuan Formation in the Xuanlong Depression of the Yanshan area is an important exploration and development region for shale gas due to its multi-layer dark shale. The [...] Read more.

The shale sedimentary environment is crucial for evaluating shale gas reservoirs and sweet spot zones. The Xiahuayuan Formation in the Xuanlong Depression of the Yanshan area is an important exploration and development region for shale gas due to its multi-layer dark shale. The paleosedimentary environment and organic matter accumulation mechanism of organic-rich shale were discussed through geochemical methods such as total organic carbon (TOC) content and elemental analysis. The results indicate that the shale exhibits a high TOC content. The Mo content and the P/Al and P/Ti ratios indicate that the primary productivity of the ancient lake is high. The Ce_anom, V/(V + Ni) ratio and Mo_EF-U_EF covariation model reveal that the sedimentary environment of shale is characterized by anoxic conditions. The ratios of K/Al and Ti/Al suggest significant variations in the input of fine-grained clay clastics and terrigenous clastics. The Ca/(Fe + Ca) and Sr/Ba ratios suggest that the paleowater was a freshwater environment. The paleoclimatic conditions, as indicated by CIA, Sr/Cu, and C-value, suggest a range from semi-humid to humid. The ratios of Rb/K and Mn/Ti reflect that the water primarily existed in a shore–shallow lake environment. The correlation analysis between organic matter accumulation and sedimentary environment parameters indicates that the primary factors influencing the organic matter accumulation in the Xiahuayuan Formation shale are redox conditions, terrigenous clastic input, paleoclimate conditions, and paleowater depth. The organic matter accumulation is characterized by a “preservation condition” pattern. This study provides theoretical support for the accumulation mechanism, potential evaluation of resources, and optimal selection of favorable regions for Jurassic shale gas in the Xuanlong Depression. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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16 pages, 7632 KiB

Open AccessArticle

The Control of Isolated Kerogen on Pore Structure and Heterogeneity in Marine-Continental Transitional Shale: A Case Study on the Taiyuan Formation, Northern Ordos Basin

by Zhengxi Gao, Ke Miao, Yushan Zuo, Fuhua Shang, Shuang Gao, Wentian Mi, Yuan Gao, Qing Li and Haidong Li

Processes 2024, 12(11), 2395; https://doi.org/10.3390/pr12112395 - 30 Oct 2024

Viewed by 954

Abstract

Accurately determining the pore structure and heterogeneity characteristics of marine-continental transitional shale in the Taiyuan Formation is crucial for evaluating the shale gas resources in the northern Ordos Basin. However, the studies on pore characteristics and heterogeneity of marine-continental transitional shales and isolated [...] Read more.

Accurately determining the pore structure and heterogeneity characteristics of marine-continental transitional shale in the Taiyuan Formation is crucial for evaluating the shale gas resources in the northern Ordos Basin. However, the studies on pore characteristics and heterogeneity of marine-continental transitional shales and isolated kerogen are limited. This study collected Taiyuan Formation shale in the northern Ordos Basin, and corresponding kerogen isolated from shale and used N₂ and CO₂ adsorption experiment and Frenkel–Halsey–Hill and Volume-Specific Surface Area model to investigate the pore structure and heterogeneity of both. The results show that the isolated kerogen is dominated by micropores, and the micropore’s specific surface area and volume are 4.7 and 3.5 times the corresponding shale, respectively. In addition, the microporous heterogeneity of the isolated kerogen is stronger than that of shale, while the mesoporous heterogeneity is exactly the opposite. Meanwhile, the micropores fractal dimension D_m is positively correlated with organic matter (OM) content, while mesopores fractal dimension D₁ and D₂ are negatively linearly correlated with TOC content and have no significant relationship with clay mineral and quartz content (but show a significant positive correlation with illite and illite/smectite mixed layer). Isolated kerogen plays an important role in the pore (especially micropores) heterogeneity of shale, while other minerals (such as clay minerals) have a controlling effect on the mesopores heterogeneity of shale. Compared with marine shale, the marine-continental transitional shale of the Taiyuan Formation has a lower fractal dimension and better connectivity, which is conducive to shale gas seepage and migration. The final result can provide a significant basis for the reserve evaluation and the optimization of desert areas in the marine-continental transitional shale gas in the northern Ordos Basin. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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24 pages, 22042 KiB

Open AccessArticle

Characterisation of the Full Pore Size Distribution of and Factors Influencing Deep Coal Reservoirs: A Case Study of the Benxi Formation in the Daning–Jixian Block at the Southeastern Margin of the Ordos Basin

by Xiaoming Chen, Tao Wang, Song Wu, Ze Deng, Julu Li, Zhicheng Ren, Daojun Huang, Wentian Fan and Gengen Zhu

Processes 2024, 12(11), 2364; https://doi.org/10.3390/pr12112364 - 28 Oct 2024

Cited by 1 | Viewed by 1004

Abstract

The complex geological environment in deep layers results in differences in the pore and fracture structures and states of coalbed methane (CBM) occurrences between deep and shallow coal reservoirs. The coexistence of multiphase gases endows deep CBM with both “conventional” and “unconventional” geological [...] Read more.

The complex geological environment in deep layers results in differences in the pore and fracture structures and states of coalbed methane (CBM) occurrences between deep and shallow coal reservoirs. The coexistence of multiphase gases endows deep CBM with both “conventional” and “unconventional” geological attributes. Based on systematically collected coal samples from the Benxi Formation in the Daning–Jixian area of the Ordos Basin, high-pressure mercury intrusion (HPMI), low-temperature N₂ adsorption (LTN₂A), and low-pressure CO₂ adsorption (LPCO₂A) experiments were conducted to characterise the pore structures across the full pore size distribution of the Benxi Formation coals. The aim of this research is to gain an in-depth understanding of the pore size distribution of full-size pores and to explore the factors influencing their pore structure and control over the gas content in coal reservoirs. The results indicate that the pore size distribution of the coal samples from the Benxi Formation in the study area is unimodal and that nanopores are present. The pore sizes are relatively small, with an average total pore volume (PV) of 0.073 cm³/g and an average total specific surface area (SSA) of 227.87 m²/g. Among these, micropores account for 92.26% of the total PV and 99.57% of the total SSA, making micropores the primary contributors to the gas storage space in the Benxi Formation coals. Mesopores and macropores contribute relatively little to the PV and SSA, which is unfavourable for CBM permeability. The development of pores in the Benxi Formation coals in the study area is influenced by the coal maturity, vitrinite content, and ash yield. Generally, the PV increases when the coal’s rank increases; an increase in the vitrinite content promotes the development of micropores, whereas a relatively high ash yield leads to decreases in the PV and SSA. The influence of the SSAs of coal pores on the gas content is reflected mainly by its effect on the adsorbed gas content. Since adsorbed gas molecules exist mainly in coal pores in the adsorbed state, the SSAs of coal pores strongly affect the storage capacity of coal for adsorbed gas. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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16 pages, 6896 KiB

Open AccessArticle

Numerical Simulation Study on Optimal CO₂ Injection Well Placement for Sequestration in Old Gob: A Case Study of the Huainan Mining Area

by Yongchun Chen, Yanfei Xu, Yuchen Tian, Helong Zhang, Bo Xue, Shiheng Chen, Yinghai Liu, Yanzhi Liu, Shiqi Liu, Shuxun Sang and Sijian Zheng

Processes 2024, 12(10), 2167; https://doi.org/10.3390/pr12102167 - 4 Oct 2024

Viewed by 1021

Abstract

The old gob, as a potential CO₂ geological storage reservoir, has huge storage potential. To clarify the distribution characteristics and storage capacity of CO₂ in the old gob after different well deployment schemes, this study, based on the actual geological conditions [...] Read more.

The old gob, as a potential CO₂ geological storage reservoir, has huge storage potential. To clarify the distribution characteristics and storage capacity of CO₂ in the old gob after different well deployment schemes, this study, based on the actual geological conditions of the old gob in the Huainan mining area, uses the COMSOL software to numerically simulate CO₂ injection into the old gob, considering the heterogeneity of permeability and the difference in coal-rock adsorption capacity within the old gob. The research indicates that the distribution characteristics of CO₂ are significantly influenced by the deployment scheme. Specifically, different deployment schemes result in varying CO₂ concentrations and distribution patterns. Particularly, when the injection well is deployed at a depth of 65 m, the distribution of CO₂ in the low-permeability upper part of the old gob will significantly increase and the horizontal distribution range will significantly decrease. Under different well deployment modes, the CO₂ storage capacity varies significantly. When the injection well is deployed at a depth of 65 m, it is more conducive to the storage of CO₂ than at other deeper depths and the total storage capacity is larger. In addition, increasing the number of monitoring wells helps the migration and diffusion of CO₂ in the old gob. Reasonably increasing the number of monitoring wells and adopting a symmetric deployment mode can significantly improve the CO₂ storage capacity in the old gob. Through a reasonable deployment scheme, the CO₂ storage capacity in the old gob can be more than 1.8 times that of the single monitoring well deployment scheme. Overall, based on the analysis of the distribution characteristics and storage capacity, the vertical positioning of the injection wells and the deployment mode of the monitoring wells that are conducive to improving the CO₂ storage capacity in the old gob are obtained, which can provide an important reference for the well deployment scheme of CO₂ storage in the old gob. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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11 pages, 6885 KiB

Open AccessArticle

Study on the Accumulation Model of the Cretaceous Reservoir in AHDEB Oilfield, Iraq

by Qiang Wang, Tao Wen, Bo Li, Jun Xin, Meng Tian and Baiyi Wu

Processes 2024, 12(10), 2135; https://doi.org/10.3390/pr12102135 - 1 Oct 2024

Viewed by 826

Abstract

The Ahdeb oil field is located in the southwestern part of the Zagros fold deformation zone. The study of the model of the formation of the oil reservoir in this field will be helpful to deepen the pattern of hydrocarbon distribution in this [...] Read more.

The Ahdeb oil field is located in the southwestern part of the Zagros fold deformation zone. The study of the model of the formation of the oil reservoir in this field will be helpful to deepen the pattern of hydrocarbon distribution in this zone. In this paper, we use the seismic data of the Ahdeb oil field to recover the tectonic evolution history of the field. Under neotectonic movement, the oil field formed in the early stage, migrated to the high point in the late stage, and finally entered the present formation. From here, for the oil-bearing inclusions within the reservoir, the photometric absorption values of the organic matter groups were measured by infrared spectroscopy. Their ratios were used to evaluate the maturity, thus discovering two phases of oil charging. Finally, using the hydrocarbon generation history and tectonic evolution history, combined with the oil and gas transportation periods in the reservoir, we deduce that the reservoir formation mode in the area is a two-phase gathering and final adjustment formation mode. This understanding of the hydrocarbon formation patterns will promote oil and gas exploration in this zone. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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15 pages, 8119 KiB

Open AccessArticle

Fracture Properties of Nitrogen–Slick Water Composite Fracturing in Coal Reservoir

by Menglong Wang, Lin Tian, Jinghao Wu, Yunxing Cao, Li Wang, Bin Shi, Mingyue Sun, Shimin Liu and Yunbing Hu

Processes 2024, 12(9), 1949; https://doi.org/10.3390/pr12091949 - 11 Sep 2024

Viewed by 816

Abstract

Nitrogen–slick water composite fracturing is a novel, recently developed fracturing technology. Due to its impact on increasing permeability, this technology outperforms hydraulic fracturing. This study adopted the horizontal well XJ-1L, Xinjing coal mine, Qinshui Basin, China, as a study area to statistically analyze [...] Read more.

Nitrogen–slick water composite fracturing is a novel, recently developed fracturing technology. Due to its impact on increasing permeability, this technology outperforms hydraulic fracturing. This study adopted the horizontal well XJ-1L, Xinjing coal mine, Qinshui Basin, China, as a study area to statistically analyze the fracture properties, stress drop, and b-value distribution characteristics of 1217 effective micro-seismic events generated during nitrogen–water composite fracturing. The results show that: (1) gradually reducing the proportion of gas in fracturing fluid reduced the proportion of tensile fractures at a ratio of between 15.6% and 0.8%, whereas the proportion of strike-slip fractures gradually increased by between 1.6% and 15.2%; (2) the stress drop and b-values in the nitrogen fracturing (NF) stage, representative of stress disturbance, exceeded those in the hydraulic fracturing (HF) stage, consistent with greater numbers of tensile fractures formed in the NF stage; (3) the greater number of tensile fractures and their increasing permeability could be explained based on the influences of gas compressibility and pore pressure on coal fractures. This study provides a theoretical and practical basis for optimizing the exploitation of low-permeability coal reservoirs. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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16 pages, 5406 KiB

Open AccessArticle

Re-Calibrating the Mercury-Intrusion-Porosimetry-Measured Pore Size Distribution of Coals: A Novel Method for Calculating the Matrix Compression Coefficient

by Bin Ren, Sijian Zheng, Lihua Ping, Meng Wang, Xuguang Dai, Yanzhi Liu, Shen Xu and Xiuping Wu

Processes 2024, 12(9), 1928; https://doi.org/10.3390/pr12091928 - 8 Sep 2024

Viewed by 1043

Abstract

Accurate measurement of the pore size distribution (PSD) in coals is crucial for guiding subsequent coalbed methane (CBM) engineering practice. Currently, mercury intrusion porosimetry (MIP) measurement has been widely used as a PSD testing method due to its effectiveness and convenience. Nevertheless, it [...] Read more.

Accurate measurement of the pore size distribution (PSD) in coals is crucial for guiding subsequent coalbed methane (CBM) engineering practice. Currently, mercury intrusion porosimetry (MIP) measurement has been widely used as a PSD testing method due to its effectiveness and convenience. Nevertheless, it is worth noting that the elevated pressure during the MIP experiments can lead to matrix compressibility, potentially causing inaccurate estimations of PSD in coals. Therefore, correction methods are used to modify the PSD in the high-pressure segment to improve the accuracy of MIP data. This study proposed a novel method with higher accuracy and convenience for calculating the matrix compressibility coefficient compared to the traditional calculation methods. Firstly, the matrix compressibility coefficients of six coal samples were calculated by using low-temperature nitrogen adsorption (LTNA) data. Subsequently, by utilizing the mathematical correlation between K_c (the compressibility coefficient of the coal matrix) and R_o,max (the maximum vitrinite reflectance) from prior research, a novel statistical method was designed to determine the matrix compressibility coefficient of the samples. Finally, the statistical matrix compressibility coefficient determination method was used to examine the fractal characteristics of the actual PSD. The results indicate that when the pressure exceeds 24 MPa, the volume obtained from mercury intrusion exceeds the pore volume measurement. The K_c calculated using the traditional correction method is in the range of 0.876–1.184 × 10⁻¹⁰ m²/N, while the K_c values of our proposed statistical correction method range from 0.898 × 10⁻¹⁰ to 1.233 × 10⁻¹⁰ m²/N, with a comparison error rate of ~0.11–5.25%. The MIP data greater than 24 MPa were effectively corrected using the statistical correction method, thus reducing the mercury intrusion volume error by 91.75–96.40%. Additionally, the corrected pore fractal dimension (D₂) values fall within the range of 2.792 to 2.975, which are closer to the actual values than the pore fractal dimension range of 3.186 to 3.339. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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14 pages, 4268 KiB

Open AccessArticle

The Analysis of Differential Saturation in Shale Oil Accompanied by an Enhanced Classification of Fluid Distribution within the Pore

by Teng Li, Xiaohang Li and Xiulan Zhu

Processes 2024, 12(9), 1870; https://doi.org/10.3390/pr12091870 - 1 Sep 2024

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Abstract

Shale oil saturated by high temperature (20 MPa) and high pressure (60 °C) conditions can not only realize the efficient saturation of shale, but also invert the shale oil return and drainage characteristics under the stratum temperature and pressure due to the heterogeneity [...] Read more.

Shale oil saturated by high temperature (20 MPa) and high pressure (60 °C) conditions can not only realize the efficient saturation of shale, but also invert the shale oil return and drainage characteristics under the stratum temperature and pressure due to the heterogeneity of shale formations. In this study, the Chang 7 Member shale samples were collected, and the high-temperature and high-pressure containment device was utilized to saturate the shale oil efficiently under 20 MPa and 60 °C, and the differences of liquid hydrocarbon saturation and the degree of liquid hydrocarbon saturation for different types of pores and fractures in the shale were quantitatively characterized with a low-field nuclear magnetic resonance (NMR) technology. The results show that under the condition of formation temperature (60 °C) and pressure (20 MPa), shale oil saturation can be reached after 14 d of saturation in the shale samples. The shale oil saturation process can be roughly divided into three stages according to the various saturation rates: the rapid saturation stage, the slow saturation stage, and the second rapid saturation stage, and the degree of saturation of shale oil is characterized by a V-shape. The shale oil was distributed into four types of pore-fracture systems: adsorption pores, micropores, seepage fractures, and layer fractures. Additionally, the fluid dominantly distributes in the micropores and seepage fractures, the shale oil saturation degree of the micropores features a continuous increase, while that for the seepage fractures presents a V-shape, which finally determines the shale oil saturation characteristics of the shale. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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21 pages, 5840 KiB

Open AccessArticle

Effects of Compositions and Fractal Pores on CO₂ Adsorption in Lacustrine Shale

by Guangjun Feng, Meng Wang, Yanming Zhu, Yu Song, Sijian Zheng, Xuguang Dai and Xuheng Wang

Processes 2024, 12(9), 1842; https://doi.org/10.3390/pr12091842 - 29 Aug 2024

Viewed by 928

Abstract

Lacustrine shale reservoirs hold promise for CO₂ geological sequestration and enhanced shale gas/oil recovery, while the CO₂ adsorption capacity and its controlling factors are still unclear in lacustrine shales. Using a volumetric-based adsorption apparatus, CO₂ adsorption experiments were performed at [...] Read more.

Lacustrine shale reservoirs hold promise for CO₂ geological sequestration and enhanced shale gas/oil recovery, while the CO₂ adsorption capacity and its controlling factors are still unclear in lacustrine shales. Using a volumetric-based adsorption apparatus, CO₂ adsorption experiments were performed at 50 °C on the Ch7 lacustrine shale samples from the Yanchang Formation in Ordos Basin, China. Basic petro-physical experiments, low-temperature N₂ adsorption, and field emission scanning electron microscopy were used to characterize shale properties and fractal pores in the lacustrine shales. Further, the effects of shale compositions and fractal pores on CO₂ adsorption capacities were serially investigated. The results show that Ch7 lacustrine shales are characterized by being rich in their TOC (total organic carbon) content, high in their clay content, but low in their quartz content, which is distinguished from the mineral compositions in marine shales. The pore size distributions are multi-modal with a main peak and two secondary peaks. Meanwhile, two-regime pore fractal characteristics were identified in the Ch7 lacustrine shales, and the fractal dimensions of the pore surface and spatial structure were calculated based on the FHH (Frenkel–Halsey–Hill) model with D₁ and D₂ ranging from 2.586–2.690 and 2.756–2.855, respectively. CO₂ adsorption isotherms present an initial phase of rapid adsorption followed by a slow saturation and were fitted using the Langmuir model with Langmuir volumes in the range of 2.16–6.89 cm³/g for Ch7 lacustrine shales. TOC is crucial for enhancing the CO₂ adsorption capacity, whereas the effect of clays on CO₂ adsorption is complex because of the reverse effects of clay-related pores and other pores filled by clays. Micropores (<2 nm) dominate the CO₂ adsorption capacity because they offer a larger unit-specific surface area and possess a higher adsorption potential compared to meso- (2–50 nm) and macro- (>50 nm) pores. Moreover, the D₁ is positively related to the CO₂ adsorption capacity as a larger D₁ coincides with more heterogeneous fractal pore surfaces and more available locations for CO₂ adsorption. This work provides useful knowledge and important data for estimating the CO₂ geological storage potential in lacustrine shale reservoirs. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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13 pages, 3205 KiB

Open AccessArticle

Method for Predicting Bound Water Saturation in Tight Sandstone Reservoirs Using Morphology and Fractal Models

by Di Zhang, Tian Tian, Yong Shi, Yaomiao He, Junjian Zhang and Zhenyuan Qin

Processes 2024, 12(9), 1811; https://doi.org/10.3390/pr12091811 - 26 Aug 2024

Cited by 2 | Viewed by 803

Abstract

The nuclear magnetic resonance T₂ spectrum was used to identify the T_2 cut-off value, which is the key to determining the irreducible water saturation of a reservoir. In this paper, the saturation and centrifugal T₂ spectra of sandstone and coal samples [...] Read more.

The nuclear magnetic resonance T₂ spectrum was used to identify the T_2 cut-off value, which is the key to determining the irreducible water saturation of a reservoir. In this paper, the saturation and centrifugal T₂ spectra of sandstone and coal samples were used to explore the correlation between each parameter and the T_2 cut-off value, using a single fractal dimension, a multifractal dimension and a spectral morphology discrimination method. The conclusions are as follows: (1) The T₂ spectra of nine sandstone samples in this paper can be divided into four types. Type A is represented by sample 2, wherein the T₂ spectrum shows a bimodal state and the area of the right T₂ spectrum (2.5~100 ms) is larger than that of the left T₂ spectrum (T₂ < 2.5 ms), indicating that the sample has good pore connectivity and belongs to the macroporous development sample. The B-type T₂ spectrum is unimodal, and the pore connectivity is poor, indicating that it is a large-pore development sample. The T₂ spectrum of the C-type sample is unimodal, and the pore connectivity is very poor, indicating that it is a mesoporous development sample. The T₂ spectrum of the D-type sample shows a single peak state, and the main T₂ is distributed within 0.1~2.5 ms. The pore connectivity is very poor, which indicates that it belongs to the small pore development type sample. (2) The single fractal model shows that, compared with other single fractal parameters, D₂ increases with the increase in the T_2 cut-off value, but the correlation is weak. Therefore, it is not feasible to predict the T_2 cut-off value using the single fractal dimension parameter. (3) The multifractal model shows that D₋₁₀–D₁₀ increases linearly with the increase in D₋₁₀–D₀, but there is no obvious linear correlation between D₀–D₁₀ and D₋₁₀–D₁₀, indicating that the low pore volume area in this kind of sample controls the overall heterogeneity of pore distribution. (4) The related parameters affecting the T_2 cut-off value include D₋₁₀–D₁₀, D₋₁₀/D₁₀, D₋₁₀–D₀, T_M and D₂. Therefore, based on the above five parameters, a T_2 cut-off value prediction model is constructed. The T_2 cut-off value calculated by the model is highly consistent with the experimental value, which proves the reliability of the model. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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12 pages, 4613 KiB

Open AccessArticle

The Strike-Slip Fault System and Its Influence on Hydrocarbon Accumulation in the Gudong Area of the Zhanhua Depression, Bohai Bay Basin

by Hongke Zhou, Qunhu Wu, Zhiwei Wang, Fei Teng, Genhou Guo, Zunxiang Zhang, Yanjia Wu and Yanjun Cheng

Processes 2024, 12(8), 1750; https://doi.org/10.3390/pr12081750 - 20 Aug 2024

Viewed by 1178

Abstract

The Gudong area contains abundant petroleum resources. Previous studies have mainly focused on the extension structure in this area, with its strike-slip characteristics remaining poorly understood. In this study, the geometry of the strike-slip faults in the Gudong area was investigated using high-resolution [...] Read more.

The Gudong area contains abundant petroleum resources. Previous studies have mainly focused on the extension structure in this area, with its strike-slip characteristics remaining poorly understood. In this study, the geometry of the strike-slip faults in the Gudong area was investigated using high-resolution 3D seismic reflection and drilling data, as were their associated releasing and restraining structures. Based on the profile’s flower structure and the plane’s horsetail splay pattern, the Gudong fault in the study area can be characterized as a dextral strike-slip. Three types of strike-slip fault-associated structures can be identified in the study area: (a) a restraining bend occurring in the right-stepping area of the S-shaped Gudong strike-slip fault, (b) a restraining bend identified in the left-stepping, overlapping zone of the Gudong and Kendong faults, and (c) a releasing bend seen in the extensional horsetail splay structure at the southern end of the Gudong fault. The restraining stress induced the formation of a fault-related open anticline, which led to a significant increase in fault sealing efficiency, thereby preserving an estimated 75.479231 million tons of oil and 15.28317145 billion cubic meters of gas. Conversely, releasing transtensional stress has compromised the effectiveness of the traps, preventing hydrocarbon retention. Consequently, oil and gas have migrated upward along the horsetail faults to the top of Cenozoic formations and have then dispersed. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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15 pages, 12040 KiB

Open AccessArticle

Geological Conditions of Shale Gas Accumulation in Coal Measures

by Fengchu Liao, Keying Wang, Jian Zhan, Zhiwei Liu, Jiang Du, Shuhua Gong, Ningbo Cai, Jianglun Bai and Junjian Zhang

Processes 2024, 12(8), 1734; https://doi.org/10.3390/pr12081734 - 18 Aug 2024

Viewed by 806

Abstract

The shale of different potential layers is studied by using rock pyrolysis analysis, total organic carbon determination (TOC), kerogen microscopic component identification, mineral X-ray diffraction, scanning electron microscopy, and low-temperature nitrogen adsorption experiments. The results are as follows: (1) Shishui Formation of the [...] Read more.

The shale of different potential layers is studied by using rock pyrolysis analysis, total organic carbon determination (TOC), kerogen microscopic component identification, mineral X-ray diffraction, scanning electron microscopy, and low-temperature nitrogen adsorption experiments. The results are as follows: (1) Shishui Formation of the Lower Carboniferous and Longtan Formation of the Upper Permian are the two most important shale gas reservoirs in the Chenlei Depression. The sedimentary environment of the target shale is a marine land interaction facies coastal bay lagoon swamp sedimentary system. Two sedimentary facies of tidal flat facies, subtidal zone, and lagoon swamp facies are developed. (2) The organic matter types of shale are Type III and II₂, with TOC content greater than 1%. The maturity of shale samples is relatively higher (R_o,max is above 2%), which means they have entered the stage of large-scale gas generation. The overall brittle mineral content of the target shale sample is relatively higher (above 40%), which is conducive to artificial fracturing and fracture formation in the later stage, while an appropriate amount of clay minerals (generally stable at 40%) is conducive to gas adsorption. (3) The overall pore structure of the water measurement group and Longtan group is good, with a higher specific surface area and total pore volume (average specific surface area is 12.21 and 8.36 m²/g, respectively), which is conducive to the occurrence of shale gas and has good adsorption and storage potential. The gas content of the water measurement group and the Longtan Formation varies from 0.42 to 5 cm³/g, with an average of 2.1 cm³/g. It indicates that the water measurement group and the Longtan Formation shale gas in the study area have good resource potential. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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22 pages, 9597 KiB

Open AccessArticle

Dynamic Change Characteristics and Main Controlling Factors of Pore Gas and Water in Tight Reservoir of Yan’an Gas Field in Ordos Basin

by Yongping Wan, Zhenchuan Wang, Meng Wang, Xiaoyan Mu, Jie Huang, Mengxia Huo, Ye Wang, Kouqi Liu and Shuangbiao Han

Processes 2024, 12(7), 1504; https://doi.org/10.3390/pr12071504 - 17 Jul 2024

Viewed by 914

Abstract

Tight sandstone gas has become an important field of natural gas development in China. The tight sandstone gas resources of Yan’an gas field in Ordos Basin have made great progress. However, due to the complex gas–water relationship, its exploration and development have been [...] Read more.

Tight sandstone gas has become an important field of natural gas development in China. The tight sandstone gas resources of Yan’an gas field in Ordos Basin have made great progress. However, due to the complex gas–water relationship, its exploration and development have been seriously restricted. The occurrence state of water molecules in tight reservoirs, the dynamic change characteristics of gas–water two-phase seepage and its main controlling factors are still unclear. In this paper, the water-occurrence state, gas–water two-phase fluid distribution and dynamic change characteristics of different types of tight reservoir rock samples in Yan’an gas field were studied by means of water vapor isothermal adsorption experiment and nuclear magnetic resonance methane flooding experiment, and the main controlling factors were discussed. The results show that water molecules in different types of tight reservoirs mainly occur in clay minerals and their main participation is in the formation of fractured and parallel plate pores. The adsorption characteristics of water molecules conform to the Dent model; that is, the adsorption is divided into single-layer adsorption, multi-layer adsorption and capillary condensation. In mudstone, limestone and fine sandstone, water mainly occurs in small-sized pores with a diameter of 0.001 μm–0.1 μm. The dynamic change characteristics of gas and water are not obvious and no longer change under 7 MPa displacement pressure, and the gas saturation is low. The gas–water dynamic change characteristics of conglomerate and medium-coarse sandstone are obvious and no longer change under 9 MPa displacement pressure. The gas saturation is high, and the water molecules mainly exist in large-sized pores with a diameter of 0.1 μm–10 μm. The development of organic matter in tight reservoir mudstone is not conducive to the occurrence of water molecules. Clay minerals are the main reason for the high water saturation of different types of tight reservoir rocks. Tight rock reservoirs with large pore size and low clay mineral content are more conducive to natural gas migration and occurrence, which is conducive to tight sandstone gas accumulation. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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17 pages, 11594 KiB

Open AccessArticle

Geochemical Characteristics and Hydrocarbon Generation Potential of Coal-Measure Source Rocks in Julu Sag

by Yang Wang, Hanyu Zhang, Liu Yang, Yanming Zhu and Zhixiang Chang

Processes 2024, 12(7), 1399; https://doi.org/10.3390/pr12071399 - 4 Jul 2024

Cited by 1 | Viewed by 1007

Abstract

To uncover the reservoir characteristics and enrichment law of coal-measure gas in Julu sag, Hebei Province, and achieve co-exploration and co-mining, it is necessary to conduct a comprehensive analysis. In this study, we investigated the characteristics of coal-measure gas accumulation in the Taiyuan [...] Read more.

To uncover the reservoir characteristics and enrichment law of coal-measure gas in Julu sag, Hebei Province, and achieve co-exploration and co-mining, it is necessary to conduct a comprehensive analysis. In this study, we investigated the characteristics of coal-measure gas accumulation in the Taiyuan Formation and Shanxi Formation in the Julu area. This was achieved by collecting data on coal-measure source rocks and organic geochemistry, which were then combined with regional geological conditions. This study indicates that the coal seams and shales of Shanxi Formation and Taiyuan Formation in the study area serve as the primary source rocks. The predominant macerals found in coal rock are vitrinite. Furthermore, the organic matter type present in shale is primarily categorized as type II₂, with the organic matter maturity falling within the immature–mature stage. Based on the simulation results of tectonic-burial history, thermal evolution history, and hydrocarbon generation history in the study area, it is evident that the coal-measure source rocks experienced their first peak of hydrocarbon generation during the Mesozoic era as a result of deep metamorphism. Subsequently, the area experienced uplift and erosion, leading to the release of coal-bearing natural gas. Since the Paleogene period, the coal-bearing source rocks have undergone sedimentary burial and entered the secondary hydrocarbon generation stage, resulting in significant production of oil and gas. Based on the analysis of gas content, buried depth, source rock thickness, and sealing conditions in the study area, it is evident that the potential of coal-measure gas resources in the study area is primarily comprised of shale gas with supplementary coalbed methane. It can be inferred that the deeper areas within the study area hold greater exploration prospects. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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12 pages, 3587 KiB

Open AccessArticle

Research on Mechanism of Surfactant Improving Wettability of Coking Coal Based on Molecular Dynamics

by Ren Liu, Shilin Li, Yuping Ling, Yuanpei Zhao and Wei Liu

Processes 2024, 12(6), 1271; https://doi.org/10.3390/pr12061271 - 20 Jun 2024

Cited by 2 | Viewed by 1154

Abstract

Coal dust is a major safety hazard in the process of coal mining and is of great importance to ensure production safety and maintain the health of operators. In order to understand the microscopic mechanism during coal seam water injection and reveal the [...] Read more.

Coal dust is a major safety hazard in the process of coal mining and is of great importance to ensure production safety and maintain the health of operators. In order to understand the microscopic mechanism during coal seam water injection and reveal the mechanism of surfactants in improving the wettability of coal dust, coking coal was selected as the research object. Three surfactants, SDBS, AEO-9, and CAB-35, were chosen for molecular dynamics simulation research on the wetting and adsorption properties of water/coal/surfactants. The results show that surfactant molecules can cover the hydrophobic groups on the surface of coking coal, forming a hydrophilic adsorption layer, changing the coal surface from hydrophobic to hydrophilic, and enhancing the wettability. After adding surfactants, the thickness of the adsorption layer in the z-axis direction increases, expanding the contact area between coking coal and water molecules, thereby improving the wettability. When surfactants tightly cover the surface of coking coal, their binding strength increases, forming a more stable hydrophilic layer and further improving the wettability. At the same time, surfactants promote the diffusion of water molecules and enhance the interaction between hydrophobic alkyl chains and water molecules, further enhancing the wetting effect. Full article

(This article belongs to the Special Issue Theoretical Progress in the Exploration and Development of Deep Coal-Measure Gas)

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