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New Challenges in Unconventional Oil and Gas Reservoirs

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H: Geo-Energy".

Deadline for manuscript submissions: closed (28 December 2023) | Viewed by 12966

Special Issue Editor

State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 100249, China
Interests: shale gas; shale oil; reservoir evaluation; accumulation mechanism

Special Issue Information

Dear Colleagues,

Unconventional oil and gas have become a major focus of research worldwide. The availability of these unconventional resources far exceeds that of conventional oil and gas. Although unconventional oil and gas were never considered valuable in the past, in the United States and China in particular, unconventional means of production have now surpassed conventional ones. Unconventional oil and gas face many new challenges as new issues arise in their exploration and development. For example, whether shale gas can migrate on a large scale and shale oil can be generated artificially have become questions requiring urgent answers.

This Special Issue aims to present and disseminate the new challenges of unconventional oil and gas reservoirs in order to promote exploration in this field.

Topics of interest for publication include, but are not limited to:

  • All aspects of shale gas, shale oil, tight gas, tight oil, coalbed methane, gas hydrate, etc.;
  • Geochemical characteristics;
  • Mineralogy and petrology characteristics;
  • Pore and fracture;
  • Tectonic evolution;
  • Accumulation conditions;
  • Geophysical interpretation;
  • Rock mechanics;
  • Geological engineering.

Dr. Xianglu Tang
Guest Editor

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Keywords

  • new challenges
  • shale gas
  • shale oil
  • tight gas
  • tight oil
  • coalbed methane
  • gas hydrate
  • geological characteristics
  • geophysical characteristics
  • geological engineering

Published Papers (12 papers)

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Research

17 pages, 5175 KiB  
Article
Reservoir Characteristics and Exploration Potential Evaluation of Lower Cambrian Niutitang Shale in Northern Guizhou: A Case Study of Well QX1
by Cong Yang, Niuniu Zou, Daquan Zhang, Yi Chen, Wei Du and Biao Zhu
Energies 2024, 17(5), 1166; https://doi.org/10.3390/en17051166 - 01 Mar 2024
Viewed by 363
Abstract
The Lower Cambrian Niutitang Formation in the Northern Guizhou harbors abundant organic-rich mud shale, constituting the most significant marine shale gas reservoir in Guizhou. In this article, the reservoir characteristics of Lower Cambrian Niutitang Formation in Northern Guizhou are analyzed in terms of [...] Read more.
The Lower Cambrian Niutitang Formation in the Northern Guizhou harbors abundant organic-rich mud shale, constituting the most significant marine shale gas reservoir in Guizhou. In this article, the reservoir characteristics of Lower Cambrian Niutitang Formation in Northern Guizhou are analyzed in terms of lithology, mineralogy, organic geochemistry, pore structure, gas content and continuous thickness of shale, and the exploration potential of shale gas in this area is evaluated. The results indicate that the content of brittle minerals in the shale of well QX1 is 65.29% to 95.22% (average of 82.10%). The total organic carbon (TOC) content ranges from 2.06% to 12.10% (average of 5.64%). The organic matter maturity (Ro) within the range of 2.29–2.67%, and the kerogen type is identified as type I. The shale samples from the Niutitang Formation have high TOC content, suitable thermal maturity, and a favorable kerogen type, suggesting good gas generation potential. The results of scanning electron microscopy (SEM) show that intergranular pores, intragranular pores and microfractures are developed in the shale of well QX1, which can provide sufficient storage space for shale gas. The shale exhibits a continuous thickness of 105.66 m in the QX1 well, comprising a gas-bearing interval of 32.89 m at the top (with an effective continuous thickness of 18 m) and a hydrocarbon source rock layer of 75.78 m at the bottom. In comparison with other shale gas regions, Niutitang Formation shale in Northern Guizhou exhibits characteristics such as favorable gas generation conditions, greater storage conditions, excellent gas-bearing, strong frackability, and substantial continuous thickness, it has greater potential for shale gas exploration. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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23 pages, 9623 KiB  
Article
Semi-Analytical Reservoir Modeling of Non-Linear Gas Diffusion with Gas Desorption Applied to the Horn River Basin Shale Gas Play, British Columbia (Canada)
by Wanju Yuan, Zhuoheng Chen, Gang Zhao, Chang Su and Bing Kong
Energies 2024, 17(3), 676; https://doi.org/10.3390/en17030676 - 31 Jan 2024
Viewed by 351
Abstract
Adsorbed gas may account for a significant part of the gas resources in shale gas and coalbed methane plays. Understanding gas sorption behaviors and integrating gas desorption into analytical reservoir modeling and an associated transient performance analysis are important for evaluating a system’s [...] Read more.
Adsorbed gas may account for a significant part of the gas resources in shale gas and coalbed methane plays. Understanding gas sorption behaviors and integrating gas desorption into analytical reservoir modeling and an associated transient performance analysis are important for evaluating a system’s gas desorption ability and further analyzing its CO2 injectability, utilization, and storage capacity. However, gas desorption, along with other pressure-dominated gas properties, increases a system’s non-linearity in theoretical studies. Few studies on analytical modeling have integrated the gas desorption feature into a non-linear system and validated the model’s accuracy. In this study, the desorbed gas due to pressure decay was treated as an additional source/sink term in the source-and-sink function methods. This method was combined with the integral image method in a semi-analytical manner to determine the amount of gas desorption. Fundamental reservoir and gas properties from the Horn River Basin shale gas play were chosen to evaluate the methodology and the performance of the associated production well. The results were compared with the commercial fine-gridding numerical simulation software, and good matches were achieved. The results showed that the desorbed gas released from rock will supply free-gas flow when the pressure significantly decreases due to gas production. The production wellbore pressure can be maintained at a higher level, and the production rate was higher than in cases where gas desorption was not considered, depending on the operating conditions. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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18 pages, 17008 KiB  
Article
Characterization of Tight Gas Sandstone Properties Based on Rock Physical Modeling and Seismic Inversion Methods
by Han Jin, Cai Liu and Zhiqi Guo
Energies 2023, 16(22), 7642; https://doi.org/10.3390/en16227642 - 17 Nov 2023
Viewed by 668
Abstract
Tight sandstones produce an increasing amount of natural gas worldwide. Apart from identifying the gas enrichment, the predictions of lithology and permeable zones are crucial for the prediction of tight gas sandstones. In the present study, a seismic inversion method is developed based [...] Read more.
Tight sandstones produce an increasing amount of natural gas worldwide. Apart from identifying the gas enrichment, the predictions of lithology and permeable zones are crucial for the prediction of tight gas sandstones. In the present study, a seismic inversion method is developed based on rock physical modeling, by which it is possible to directly predict the lithology and pore structure in tight formations. The double-porosity model is used as a modeling tool in considering complex pore structures. Based on the model, the microfracture porosity is then predicted using logging data, which are used as a factor to estimate microfractures. Parameters representing the lithology and pore structure are proposed and estimated using logging data analyses and rock physical modeling based on the framework of the Poisson impedance. Thereafter, a new AVO equation is established and extended to the form of an elastic impedance for a direct prediction of the lithology and pore structure parameters. Real data applications show that the indicators of lithology and permeable zones are consistent with the production status. They agree with the petrophysical properties measured in wellbores, thereby proving the applicability of the proposed method for the effective characterization of tight gas sandstones. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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19 pages, 10033 KiB  
Article
Geophysical Interpretation of Horizontal Fractures in Shale Oil Reservoirs Using Rock Physical and Seismic Methods
by Zhiqi Guo, Wenxuan Gao and Cai Liu
Energies 2023, 16(22), 7514; https://doi.org/10.3390/en16227514 - 09 Nov 2023
Viewed by 494
Abstract
Horizontal fractures are one of the factors that significantly affect the ultimate productivity of shale oil reservoirs. However, the prediction of horizontal fractures by using seismic methods remains a challenge, which is due to the complex elastic and seismic responses that are associated [...] Read more.
Horizontal fractures are one of the factors that significantly affect the ultimate productivity of shale oil reservoirs. However, the prediction of horizontal fractures by using seismic methods remains a challenge, which is due to the complex elastic and seismic responses that are associated with horizontal fractures. A framework that predicts horizontal fractures by seismic rock physical methods has been developed in the present study. A shale model is then proposed to quantify the shale elastic responses that are associated with the properties of the horizontal fractures. The modeling results that are based on the logging data validated the applicability of the proposed model, and the predicted fracture properties could be used to evaluate the development of horizontal fractures. According to the framework of the Poisson impedance, a horizontal fracture indicator is suggested to represent the logging-derived fracture density in terms of a combination of elastic properties. By using seismic-inverted elastic properties, the obtained indicator enabled an estimation of zones with the potential development of horizontal fractures. The established indicator showed a good correlation with the fracture density and could be used as an effective indicator in the prediction of horizontal fractures in shale oil reservoirs. Furthermore, seismic data applications show a consistency between the development of horizontal fractures and the production status of the boreholes. This result highlights the importance of horizontal fractures for the ultimate productivity and emphasizes the applicability of the proposed methods. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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15 pages, 5908 KiB  
Article
Pore Water and Its Multiple Controlling Effects on Natural Gas Enrichment of the Quaternary Shale in Qaidam Basin, China
by Xianglu Tang, Zhenxue Jiang, Zhenglian Yuan, Yifan Jiao, Caihua Lin and Xiaoxue Liu
Energies 2023, 16(17), 6170; https://doi.org/10.3390/en16176170 - 25 Aug 2023
Viewed by 656
Abstract
Quaternary shale gas resources are abundant in the world, but Quaternary shale contains a lot of pore water, which affects the enrichment of shale gas. At present, the controlling effect of pore water on gas enrichment in Quaternary shale is not clear. Taking [...] Read more.
Quaternary shale gas resources are abundant in the world, but Quaternary shale contains a lot of pore water, which affects the enrichment of shale gas. At present, the controlling effect of pore water on gas enrichment in Quaternary shale is not clear. Taking the Quaternary shale of Qaidam Basin, China as an example, this paper systematically studies the characteristics of pore water in Quaternary shale through X-ray diffraction rock analysis, nuclear magnetic resonance, methane isothermal adsorption and other experiments, and reveals the controlling effect of pore water on shale gas enrichment. The results show that clay shale and silty shale are mainly developed in Quaternary shale. The clay shale is more hydrophilic, and water mainly exists in micropores and mesopores. Silty shale is less hydrophilic, and water mainly exists in mesopores and macropores. Pore water controls the formation of shale gas by the content of potassium and sodium ions, controls the adsorption of shale gas by occupying the adsorption point on the pore surface, controls the flow of shale gas by occupying the pore space, and controls the occurrence of shale gas by forming water film. Therefore, pore water has multiple controlling effects on shale gas enrichment. This achievement is significant in enriching shale gas geological theory and guide shale gas exploration. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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21 pages, 10479 KiB  
Article
Hydrocarbon Generation Mechanism of Mixed Siliciclastic–Carbonate Shale: Implications from Semi–Closed Hydrous Pyrolysis
by Jian Wang, Jun Jin, Jin Liu, Jingqiang Tan, Lichang Chen, Haisu Cui, Xiao Ma and Xueqi Song
Energies 2023, 16(7), 3065; https://doi.org/10.3390/en16073065 - 28 Mar 2023
Viewed by 1017
Abstract
Affected by the complex mechanism of organic–inorganic interactions, the generation–retention–expulsion model of mixed siliciclastic–carbonate sediments is more complicated than that of common siliciclastic and carbonate shale deposited in lacustrine and marine environments. In this study, mixed siliciclastic–carbonate shale from Lucaogou Formation in Junggar [...] Read more.
Affected by the complex mechanism of organic–inorganic interactions, the generation–retention–expulsion model of mixed siliciclastic–carbonate sediments is more complicated than that of common siliciclastic and carbonate shale deposited in lacustrine and marine environments. In this study, mixed siliciclastic–carbonate shale from Lucaogou Formation in Junggar Basin was selected for semi–closed hydrous pyrolysis experiments, and seven experiments were conducted from room temperature to 300, 325, 350, 375, 400, 450, and 500 °C, respectively. The quantities and chemical composition of oil, gases, and bitumen were comprehensively analyzed. The results show that the hydrocarbon generation stage of shale in Lucaogou Formation can be divided into kerogen cracking stage (300–350 °C), peak oil generation stage (350–400 °C), wet gas generation stage (400–450 °C), and gas secondary cracking stage (450–500 °C). The liquid hydrocarbon yield (oil + bitumen) reached the peak of 720.42 mg/g TOC at 400 °C. The saturate, aromatic, resin, and asphaltine percentages of bitumen were similar to those of crude oil collected from Lucaogou Formation, indicating that semi–closed pyrolysis could stimulate the natural hydrocarbon generation process. Lucaogou shale does not strictly follow the “sequential” reaction model of kerogen, which is described as kerogen firstly generating the intermediate products of heavy hydrocarbon compounds (NSOs) and NSOs then cracking to generate oil and gas. Indeed, the results of this study show that the generation of oil and gas was synchronous with that of NSOs and followed the “alternate pathway” mechanism during the initial pyrolysis stage. The hydrocarbon expulsion efficiency sharply increased from an average of 27% to 97% at 450 °C, meaning that the shale retained considerable amounts of oil below 450 °C. The producible oil reached the peak yield of 515.45 mg/g TOC at 400 °C and was synchronous with liquid hydrocarbons. Therefore, 400 °C is considered the most suitable temperature for fracturing technology. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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27 pages, 8301 KiB  
Article
Method Selection for Analyzing the Mesopore Structure of Shale—Using a Combination of Multifractal Theory and Low-Pressure Gas Adsorption
by Meng Wang, Zhuo Li, Zhikai Liang, Zhenxue Jiang and Wei Wu
Energies 2023, 16(5), 2464; https://doi.org/10.3390/en16052464 - 04 Mar 2023
Cited by 4 | Viewed by 1364
Abstract
Nitrogen adsorption experiments have been extensively applied to shale pore structure research and evaluation. The pore structure can be quantitatively characterized in accordance with the nitrogen adsorption–desorption isotherm using various calculation models, whereas the results obtained using different models can more effectively indicate [...] Read more.
Nitrogen adsorption experiments have been extensively applied to shale pore structure research and evaluation. The pore structure can be quantitatively characterized in accordance with the nitrogen adsorption–desorption isotherm using various calculation models, whereas the results obtained using different models can more effectively indicate the pore characteristics of shale remains unclear. Further, there has not been any unified process in the optimization of calculation models for pore size distribution (PSD). In this study, the Barret–Joyner–Halenda adsorption (BJH-AD) and BJH desorption (BJH-DE) models were used with Longmaxi Formation shale as an example. Subsequently, the density functional theory (DFT) calculations were conducted on different shale lithofacies samples. Next, the pore structure parameters and heterogeneity obtained using different models were compared, and the consistency parameters of different models were obtained in accordance with Cronbach’s alpha. The results indicated that the pore structure parameters obtained using the BJH-AD model were underestimated since the macroscopic thermodynamic theory was not applicable to this study. The DFT model showed multiple peaks in the range of 1–10 nm, whereas the BJH-DE model had a significant artificial peak in the range of 3.8 nm due to the tensile strength effect, thus suggesting that the DFT model is more capable of characterizing the pores with a pore size 10 nm lower than the BJH model. The PSD curves generated using the three models exhibited multifractal characteristics, whereas the results of the heterogeneity achieved using different models were different. Moreover, the consistency of the results of different models can be studied in depth by combining Cronbach’s alpha with various heterogeneity parameters. The DFT model exhibited high consistency in pore structure parameters and pore heterogeneity, thus suggesting that the DFT method of N2 is the optimal physical adsorption data analysis method in the shale mesoporous range. Accordingly, the nitrogen adsorption curve, the hysteresis loop shape, multifractal parameters, and Cronbach’s alpha were integrated to generate a working flow chart of the nitrogen adsorption model for N2-adsorption-model optimization. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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19 pages, 5672 KiB  
Article
Geochemical Characteristics of Graptolite Shale in the Pingliang Formation of the Ordos Basin, China: Implications for Organic Matter, Thermal Evolution, and Hydrocarbon Reservoir
by Fengjiao Li, Zhengliang Huang, Xiaofeng Wang, Xiaofeng Liu, Wenhui Liu, Zhenghong Cai, Houyong Luo, Qingtao Wang and Dongdong Zhang
Energies 2022, 15(21), 8238; https://doi.org/10.3390/en15218238 - 04 Nov 2022
Cited by 1 | Viewed by 1189
Abstract
Graptolite-rich shale is the main layer of shale gas resources in the southern marine sedimentary basin. Recently, shale gas resources were discovered in the Ordovician marine graptolite-rich strata in the Ordos Basin. The graptolite shale in the study area is different from the [...] Read more.
Graptolite-rich shale is the main layer of shale gas resources in the southern marine sedimentary basin. Recently, shale gas resources were discovered in the Ordovician marine graptolite-rich strata in the Ordos Basin. The graptolite shale in the study area is different from the marine graptolite shale in the Yangtze plate in southern China, and further exploration is needed. This paper presents core samples of the graptolite-rich shale of the Pingliang Formation in the southwest Ordos Basin as research objects. The graptolite genus and graptolite shale characteristics were studied using core observation, electron microscopy, scanning electron microscopy, and geochemical analysis. We determined the role of the sedimentary environment and thermal maturation of graptolite shale in hydrocarbon formation and explored the possibility of hydrocarbon generation. Many graptolite epidermises provide buried organic matter. The quiet sea and low-energy marine environment create favorable conditions for preserving organic matter. The tectonic process resulted in the evolution stage in the oil generation window. Different types of pores formed the spaces of hydrocarbons. Therefore, the shale of the Pingliang Formation has shale oil exploration potential, which complements the shale gas in the northwestern margin of the basin, and provides new venues for shale oil and gas exploration in northern China. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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19 pages, 3679 KiB  
Article
Controlling Factors and Forming Types of Deep Shale Gas Enrichment in Sichuan Basin, China
by Xuewen Shi, Wei Wu, Qiuzi Wu, Kesu Zhong, Zhenxue Jiang and Huan Miao
Energies 2022, 15(19), 7023; https://doi.org/10.3390/en15197023 - 24 Sep 2022
Cited by 4 | Viewed by 1350
Abstract
In order to find out the enrichment mechanism and forming type of deep shale gas, taking the Longmaxi Formation shale in the Desheng–Yunjin Syncline area of Sichuan Basin as an example, we determined the mineralogy, organic geochemistry, physical property analysis, gas and water [...] Read more.
In order to find out the enrichment mechanism and forming type of deep shale gas, taking the Longmaxi Formation shale in the Desheng–Yunjin Syncline area of Sichuan Basin as an example, we determined the mineralogy, organic geochemistry, physical property analysis, gas and water content, and the influence of three factors, namely sedimentation, structural conditions, and hydrogeological conditions, on the enrichment of shale gas. The results show that Longmaxi Formation shale in Desheng–Yunjin Syncline area is a good hydrocarbon source rock that is in the over-mature stage and has the characteristics of high porosity, low permeability, and high-water saturation. The contents of clay and quartz are high, and the brittleness index is quite different. According to the mineral composition, nine types of lithofacies can be found. The development characteristics of Longmaxi Formation shale and the sealing property of the roof have no obvious influence on the enrichment of shale gas, but the tectonic activities and hydrodynamic conditions have obvious influence on the enrichment of shale gas. The main control factors for shale gas enrichment in different regions are different. According to the main control factors, the gas accumulation in the study area can be divided into three types: fault-controlled gas, anticline-controlled gas, and hydrodynamic-controlled gas. The fault-controlled gas type is distributed in the north of the Desheng syncline and the north of the Yunjin syncline, the anticline-controlled gas type is distributed in the south of the Desheng syncline and the south of the Yunjin syncline, and the hydrodynamic-controlled gas type is distributed in the middle of the Baozang syncline. This result is of great significance for deep shale gas exploration. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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25 pages, 38961 KiB  
Article
Influence of Multi-Period Tectonic Movement and Faults on Shale Gas Enrichment in Luzhou Area of Sichuan Basin, China
by Xuewen Shi, Wei Wu, Yuguang Shi, Zhenxue Jiang, Lianbo Zeng, Shijie Ma, Xindi Shao, Xianglu Tang and Majia Zheng
Energies 2022, 15(18), 6846; https://doi.org/10.3390/en15186846 - 19 Sep 2022
Cited by 2 | Viewed by 1490
Abstract
The Luzhou area in the southern Sichuan Basin has experienced multiple tectonic movements, forming a complex fault system; the activity has an important impact on the enrichment of shale gas in this area. In order to reveal the influence of the fracture system [...] Read more.
The Luzhou area in the southern Sichuan Basin has experienced multiple tectonic movements, forming a complex fault system; the activity has an important impact on the enrichment of shale gas in this area. In order to reveal the influence of the fracture system on the differential enrichment of shale gas, this paper takes the southern Sichuan Basin as the research object. The structural evolution process and fracture development characteristics of the different tectonic units in Luzhou area of southern Sichuan were characterized by conducting a seismic profile analysis, structural recovery using a back-stripping method, and core hand specimen description. We clarified the control effect of the structural deformation and fracture on the differential enrichment of shale gas, and we established a differential enrichment model of shale gas in the Luzhou area. The results show that: (1) The Luzhou area has undergone the transformation of a multi-stage tectonic movement. There are many sets of detachment structures in the longitudinal direction, and the plane structural form is a thin-skin fold-thrust belt composed of wide and narrow anticlines in the north–south direction. (2) The faults in the study area are affected by the Himalayan tectonic movement. The high-angle reverse faults are developed, and the number of large faults is small. The second and third faults are mainly developed. The second faults are only developed at the high position of the structure, which has a significantly destructive effect on shale gas reservoirs, while the third and fourth faults have no significant destructive effect on shale gas reservoirs. (3) In the study area, the types of cracks are categorized into transformational shear cracks, bed-parallel shear cracks, intraformational open cracks, lamellation cracks, shrinkage cracks, and abnormal high-pressure cracks. The thickness of the shale rock mechanical layer, brittle mineral content, and organic matter content jointly control the crack development degree in the shale of the Wufeng–Longmaxi Formation. (4) The uplift erosion, structural deformation, and fracture development caused by the structural evolution have affected the preservation of shale gas, resulting in the differential enrichment of shale gas reservoirs in the region. Based on the enrichment factors of shale gas, we established a differential enrichment model of shale gas in typical structural units and optimized the favorable enrichment areas, which are important contributions for guiding shale gas exploration and development in the Sichuan Basin. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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29 pages, 7042 KiB  
Article
Differential Reservoir-Forming Mechanisms of the Lower Paleozoic Wufeng-Longmaxi and Niutitang Marine Gas Shales in Northern Guizhou Province, SW China: Theories and Models
by Wei Du, Wei Yang, Xingyu Li, Fulun Shi, Ruiqin Lin, Yisong Wang, Daquan Zhang, Yi Chen, Zhao Sun and Fuping Zhao
Energies 2022, 15(14), 5137; https://doi.org/10.3390/en15145137 - 15 Jul 2022
Cited by 1 | Viewed by 1236
Abstract
Fine dissection of microscopic pore structure variations between the Niutitang Formation and the Wufeng-Longmaxi Formation will help to improve the understanding of the underlying geological theory of shale gas in northern Guizhou Province. The stratigraphic, geochemical, physical, and tectonic properties of the two [...] Read more.
Fine dissection of microscopic pore structure variations between the Niutitang Formation and the Wufeng-Longmaxi Formation will help to improve the understanding of the underlying geological theory of shale gas in northern Guizhou Province. The stratigraphic, geochemical, physical, and tectonic properties of the two formations vary greatly, resulting in differential development of the microscopic pore structure among reservoirs and, as a result, major variances in gas concentration. To explore the mechanism of differential pore evolution, experimental techniques and instruments such as gas adsorption, liquid intrusion, SEM, XRD, and organic geochemical tests were utilized. The results indicate that the Wufeng-Longmaxi Formation is in a high-maturity stage, while the Niutitang Formation is in an over-mature stage. The latter has a higher TOC content. Both petrographic phases are siliceous shale petrographic phases, and the former has more developed dissolution pores with better pore volume, throat radius, and macropore pore diameters than the latter, as well as organic matter pores, intergranular pores, and microfracture structural parameters, whereas the specific surface area is the opposite. The differences in reservoir pore formation between the two formations were analyzed, and the results showed that the petrographic type, thermal evolution, and tectonic preservation conditions were the primary controlling elements of differential shale gas reservoir formation. A differential reservoir-forming model of the Wufeng-Longmaxi Formation and the Niutitang Formation was constructed, providing a geological and theoretical basis for shale gas geological exploration in northern Guizhou Province. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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20 pages, 5724 KiB  
Article
Dynamic Accumulation of the Quaternary Shale Biogas in Sanhu Area of the Qaidam Basin, China
by Zeyu Shao, Shijie He, Lili Hou, Yuchao Wang, Cong Tian, Xiaoxue Liu, Yuru Zhou, Mianzhu Hao and Caihua Lin
Energies 2022, 15(13), 4593; https://doi.org/10.3390/en15134593 - 23 Jun 2022
Cited by 4 | Viewed by 1395
Abstract
Biogas resources in the Sanhu area of the Qaidam Basin have great potential, but there are few studies on biogas from shale, especially on the accumulation conditions of shale biogas. The study of biogas accumulation conditions of quaternary shale in the Sanhu area [...] Read more.
Biogas resources in the Sanhu area of the Qaidam Basin have great potential, but there are few studies on biogas from shale, especially on the accumulation conditions of shale biogas. The study of biogas accumulation conditions of quaternary shale in the Sanhu area is of great significance to the theory of biogas accumulation and the guidance of exploration and development. This paper takes Quaternary shale in the Sanhu area as the research object. It is analyzed from multiple perspectives of shale hydrocarbon generation conditions, reservoir conditions, as well as hydrodynamic and structural conditions. Through the experiments of soluble organic carbon analysis and porosity and permeability analysis, the accumulation conditions of shale biogas reservoirs are clarified. The results show that the quaternary shale has a high soluble organic carbon content and high salinity formation water, which is conducive to late methane biochemical generation. Quaternary shale has the characteristics of high porosity and low permeability, mainly developing intergranular pores and intragranular pores. The large pore volume and specific surface area provide a lot of storage space for free gas and adsorbed gas, and the reservoir conditions are good. Under the structural characteristics of high in the south and low in the north and the action of formation hydrodynamics, biogas migrated from the south and deep to the north of the basin. The north slope is the main biogas-rich zone. On the whole, the quaternary shale in the Sanhu area has the characteristics of continuous hydrocarbon generation and dynamic accumulation, which has huge resource potential and exploration and development value. Full article
(This article belongs to the Special Issue New Challenges in Unconventional Oil and Gas Reservoirs)
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