Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60007-3
Xianyang LIU , Jiangyan LIU , Xiujuan WANG , Qiheng GUO , Lv Qiqi , Zhi YANG , Yan ZHANG , Zhongyi ZHANG , Wenxuan ZHANG
<div><div>Based on recent advancements in shale oil exploration within the Ordos Basin, this study presents a comprehensive investigation of the paleoenvironment, lithofacies assemblages and distribution, depositional mechanisms, and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins, with a focus on the Chang 7<sub>3</sub> sub-member of Triassic Yanchang Formation. The research integrates a variety of exploration data, including field outcrops, drilling, logging, core samples, geochemical analyses, and flume simulation. The study indicates that: (1) The paleoenvironment of the Chang 7<sub>3</sub> deposition is characterized by a warm and humid climate, frequent monsoon events, and a large water depth of freshwater lacustrine basin. The paleogeomorphology exhibits an asymmetrical pattern, with steep slopes in the southwest and gentle slopes in the northeast, which can be subdivided into microgeomorphological units, including depressions and ridges in lakebed, as well as ancient channels. (2) The Chang 7<sub>3</sub> sub-member is characterized by a diverse array of fine-grained sediments, including very fine sandstone, siltstone, mudstone and tuff. These sediments are primarily distributed in thin interbedded and laminated arrangements vertically. The overall grain size of the sandstone predominantly falls below 62.5 μm, with individual layer thicknesses of 0.05–0.64 m. The deposits contain intact plant fragments and display various sedimentary structure, such as wavy bedding, inverse-to-normal grading sequence, and climbing ripple bedding, which indicating a depositional origin associated with density flows. (3) Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows. The initial phase is characterized by a density-velocity differential, resulting in a thicker, coarser sediment layer at the flow front, while the upper layers are thinner and finer in grain size. During the mid-phase, sliding water effects cause the fluid front to rise and facilitate rapid forward transport. This process generates multiple “new fronts”, enabling the long-distance transport of fine-grained sandstones, such as siltstone and argillaceous siltstone, into the center of the lake basin. (4) A sedimentary model primarily controlled by hyperpynal flows was established for the southwestern part of the basin, highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows. (5) Sandstone and mudstone in the Chang 7<sub>3</sub> sub-member exhibit micro- and nano-scale pore-throat systems, shale oil is present in various lithologies, while the content of movable oil varies considerably, with sandstone exhibiting the highest content of movable oil. (6) The fine-grained sediment complexes formed by multiple episodes of
{"title":"Mechanisms of fine-grained sedimentation and reservoir characteristics of shale oil in continental freshwater lacustrine basin: A case study from Chang 73 sub-member of Triassic Yanchang Formation in southwestern Ordos Basin, NW China","authors":"Xianyang LIU , Jiangyan LIU , Xiujuan WANG , Qiheng GUO , Lv Qiqi , Zhi YANG , Yan ZHANG , Zhongyi ZHANG , Wenxuan ZHANG","doi":"10.1016/S1876-3804(25)60007-3","DOIUrl":"10.1016/S1876-3804(25)60007-3","url":null,"abstract":"<div><div>Based on recent advancements in shale oil exploration within the Ordos Basin, this study presents a comprehensive investigation of the paleoenvironment, lithofacies assemblages and distribution, depositional mechanisms, and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins, with a focus on the Chang 7<sub>3</sub> sub-member of Triassic Yanchang Formation. The research integrates a variety of exploration data, including field outcrops, drilling, logging, core samples, geochemical analyses, and flume simulation. The study indicates that: (1) The paleoenvironment of the Chang 7<sub>3</sub> deposition is characterized by a warm and humid climate, frequent monsoon events, and a large water depth of freshwater lacustrine basin. The paleogeomorphology exhibits an asymmetrical pattern, with steep slopes in the southwest and gentle slopes in the northeast, which can be subdivided into microgeomorphological units, including depressions and ridges in lakebed, as well as ancient channels. (2) The Chang 7<sub>3</sub> sub-member is characterized by a diverse array of fine-grained sediments, including very fine sandstone, siltstone, mudstone and tuff. These sediments are primarily distributed in thin interbedded and laminated arrangements vertically. The overall grain size of the sandstone predominantly falls below 62.5 μm, with individual layer thicknesses of 0.05–0.64 m. The deposits contain intact plant fragments and display various sedimentary structure, such as wavy bedding, inverse-to-normal grading sequence, and climbing ripple bedding, which indicating a depositional origin associated with density flows. (3) Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows. The initial phase is characterized by a density-velocity differential, resulting in a thicker, coarser sediment layer at the flow front, while the upper layers are thinner and finer in grain size. During the mid-phase, sliding water effects cause the fluid front to rise and facilitate rapid forward transport. This process generates multiple “new fronts”, enabling the long-distance transport of fine-grained sandstones, such as siltstone and argillaceous siltstone, into the center of the lake basin. (4) A sedimentary model primarily controlled by hyperpynal flows was established for the southwestern part of the basin, highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows. (5) Sandstone and mudstone in the Chang 7<sub>3</sub> sub-member exhibit micro- and nano-scale pore-throat systems, shale oil is present in various lithologies, while the content of movable oil varies considerably, with sandstone exhibiting the highest content of movable oil. (6) The fine-grained sediment complexes formed by multiple episodes of ","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 95-111"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464693","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60016-4
Dingwei WENG , Qiang SUN , Hongbo LIANG , Qun LEI , Baoshan GUAN , Lijun MU , Hanbin LIU , Shaolin ZHANG , Lin CHAI , Rui HUANG
A flexible sidetracking stimulation technology of horizontal wells is formed to develop the lateral deep remaining oil and gas resources of the low-permeability mature oilfields. This technology first uses the flexible sidetracking tool to achieve low-cost sidetracking in the old wellbore, and then uses the hydraulic jet technology to induce multiple fractures to fracture. Finally, the bullhead fracturing of multi-cluster temporary plugging for the sidetracking hole is carried out by running the tubing string, to realize the efficient development of the remaining reserves among the wells. The flexible sidetracking stimulation technology involves flexible sidetracking horizontal wells drilling and sidetracking horizontal well fracturing. The flexible sidetracking horizontal well drilling includes three aspects: flexible drill pipe structure and material optimization, drilling technology, and sealed coring tool. The sidetracking horizontal well fracturing includes two aspects: fracturing scheme optimization, fracturing tools and implementation process optimization. The technology has been conducted several rounds of field tests in the Ansai Oilfield of Changqing, China. The results show that by changing well type and reducing row spacing of oil and water wells, the pressure displacement system can be well established to achieve effective pressure transmission and to achieve the purpose of increasing liquid production in low-yield and low-efficiency wells. It is verified that the flexible sidetracking stimulation technology can provide favorable support for accurately developing remaining reserves in low-permeability reservoirs.
{"title":"Flexible sidetracking stimulation technology of horizontal wells in low-permeability mature oilfields","authors":"Dingwei WENG , Qiang SUN , Hongbo LIANG , Qun LEI , Baoshan GUAN , Lijun MU , Hanbin LIU , Shaolin ZHANG , Lin CHAI , Rui HUANG","doi":"10.1016/S1876-3804(25)60016-4","DOIUrl":"10.1016/S1876-3804(25)60016-4","url":null,"abstract":"<div><div>A flexible sidetracking stimulation technology of horizontal wells is formed to develop the lateral deep remaining oil and gas resources of the low-permeability mature oilfields. This technology first uses the flexible sidetracking tool to achieve low-cost sidetracking in the old wellbore, and then uses the hydraulic jet technology to induce multiple fractures to fracture. Finally, the bullhead fracturing of multi-cluster temporary plugging for the sidetracking hole is carried out by running the tubing string, to realize the efficient development of the remaining reserves among the wells. The flexible sidetracking stimulation technology involves flexible sidetracking horizontal wells drilling and sidetracking horizontal well fracturing. The flexible sidetracking horizontal well drilling includes three aspects: flexible drill pipe structure and material optimization, drilling technology, and sealed coring tool. The sidetracking horizontal well fracturing includes two aspects: fracturing scheme optimization, fracturing tools and implementation process optimization. The technology has been conducted several rounds of field tests in the Ansai Oilfield of Changqing, China. The results show that by changing well type and reducing row spacing of oil and water wells, the pressure displacement system can be well established to achieve effective pressure transmission and to achieve the purpose of increasing liquid production in low-yield and low-efficiency wells. It is verified that the flexible sidetracking stimulation technology can provide favorable support for accurately developing remaining reserves in low-permeability reservoirs.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 219-229"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464787","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60010-3
Lianbo ZENG , Yichen SONG , Jun HAN , Jianfa HAN , Yingtao YAO , Cheng HUANG , Yintao ZHANG , Xiaolin TAN , Hao LI
This study comprehensively uses various methods such as production dynamic analysis, fluid inclusion thermometry and carbon-oxygen isotopic compositions testing, based on outcrop, core, well-logging, 3D seismic, geochemistry experiment and production test data, to systematically explore the control mechanisms of structure and fluid on the scale, quality, effectiveness and connectivity of ultra-deep fault-controlled carbonate fractured-vuggy reservoirs in the Tarim Basin. The results show that reservoir scale is influenced by strike-slip fault scale, structural position, and mechanical stratigraphy. Larger faults tend to correspond to larger reservoir scales. The reservoir scale of contractional overlaps is larger than that of extensional overlaps, while pure strike-slip segments are small. The reservoir scale is enhanced at fault intersection, bend, and tip segments. Vertically, the heterogeneity of reservoir development is controlled by mechanical stratigraphy, with strata of higher brittleness indices being more conducive to the development of fractured-vuggy reservoirs. Multiple phases of strike-slip fault activity and fluid alterations contribute to fractured-vuggy reservoir effectiveness evolution and heterogeneity. Meteoric water activity during the Late Caledonian to Early Hercynian period was the primary phase of fractured-vuggy reservoir formation. Hydrothermal activity in the Late Hercynian period further intensified the heterogeneity of effective reservoir space distribution. The study also reveals that fractured-vuggy reservoir connectivity is influenced by strike-slip fault structural position and present in-situ stress field. The reservoir connectivity of extensional overlaps is larger than that of pure strike-slip segments, while contractional overlaps show worse reservoir connectivity. Additionally, fractured-vuggy reservoirs controlled by strike-slip faults that are nearly parallel to the present in-situ stress direction exhibit excellent connectivity. Overall, high-quality reservoirs are distributed at the fault intersection of extensional overlaps, the central zones of contractional overlaps, pinnate fault zones at intersection, bend, and tip segments of pure strike-slip segments. Vertically, they are concentrated in mechanical stratigraphy with high brittleness indices.
{"title":"Control of structure and fluid on ultra-deep fault-controlled carbonate fracture-vug reservoirs in the Tarim Basin, NW China","authors":"Lianbo ZENG , Yichen SONG , Jun HAN , Jianfa HAN , Yingtao YAO , Cheng HUANG , Yintao ZHANG , Xiaolin TAN , Hao LI","doi":"10.1016/S1876-3804(25)60010-3","DOIUrl":"10.1016/S1876-3804(25)60010-3","url":null,"abstract":"<div><div>This study comprehensively uses various methods such as production dynamic analysis, fluid inclusion thermometry and carbon-oxygen isotopic compositions testing, based on outcrop, core, well-logging, 3D seismic, geochemistry experiment and production test data, to systematically explore the control mechanisms of structure and fluid on the scale, quality, effectiveness and connectivity of ultra-deep fault-controlled carbonate fractured-vuggy reservoirs in the Tarim Basin. The results show that reservoir scale is influenced by strike-slip fault scale, structural position, and mechanical stratigraphy. Larger faults tend to correspond to larger reservoir scales. The reservoir scale of contractional overlaps is larger than that of extensional overlaps, while pure strike-slip segments are small. The reservoir scale is enhanced at fault intersection, bend, and tip segments. Vertically, the heterogeneity of reservoir development is controlled by mechanical stratigraphy, with strata of higher brittleness indices being more conducive to the development of fractured-vuggy reservoirs. Multiple phases of strike-slip fault activity and fluid alterations contribute to fractured-vuggy reservoir effectiveness evolution and heterogeneity. Meteoric water activity during the Late Caledonian to Early Hercynian period was the primary phase of fractured-vuggy reservoir formation. Hydrothermal activity in the Late Hercynian period further intensified the heterogeneity of effective reservoir space distribution. The study also reveals that fractured-vuggy reservoir connectivity is influenced by strike-slip fault structural position and present in-situ stress field. The reservoir connectivity of extensional overlaps is larger than that of pure strike-slip segments, while contractional overlaps show worse reservoir connectivity. Additionally, fractured-vuggy reservoirs controlled by strike-slip faults that are nearly parallel to the present in-situ stress direction exhibit excellent connectivity. Overall, high-quality reservoirs are distributed at the fault intersection of extensional overlaps, the central zones of contractional overlaps, pinnate fault zones at intersection, bend, and tip segments of pure strike-slip segments. Vertically, they are concentrated in mechanical stratigraphy with high brittleness indices.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 143-156"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60002-4
Xusheng GUO , Ruyue WANG , Baojian SHEN , Guanping WANG , Chengxiang WAN , Qianru WANG
By reviewing the research progress and exploration practices of shale gas geology in China, analyzing and summarizing the geological characteristics, enrichment laws, and resource potential of different types of shale gas, the following understandings have been obtained: (1) Marine, transitional, and lacustrine shales in China are distributed from old to new in geological age, and the complexity of tectonic reworking and hydrocarbon generation evolution processes gradually decreases. (2) The sedimentary environment controls the type of source-reservoir configuration, which is the basis of “hydrocarbon generation and reservoir formation”. The types of source-reservoir configuration in marine and lacustrine shales are mainly source-reservoir integration, with occasional source-reservoir separation. The configuration types of transitional shale are mainly source-reservoir integration and source-reservoir symbiosis. (3) The resistance of rigid minerals to compression for pore preservation and the overpressure facilitate the enrichment of source-reservoir integrated shale gas. Good source reservoir coupling and preservation conditions are crucial for the shale gas enrichment of source-reservoir symbiosis and source-reservoir separation types. (4) Marine shale remains the main battlefield for increasing shale gas reserves and production in China, while transitional and lacustrine shales are expected to become important replacement areas. It is recommended to carry out the shale gas exploration at three levels: Accelerate the exploration of Silurian, Cambrian, and Permian marine shales in the Upper-Middle Yangtze region; make key exploration breakthroughs in ultra-deep marine shales of the Upper-Middle Yangtze region, the new Ordovician marine shale strata in the North China region, the transitional shales of the Carboniferous and Permian, as well as the Mesozoic lacustrine shale gas in basins such as Sichuan, Ordos and Songliao; explore and prepare for new shale gas exploration areas such as South China and Northwest China, providing technology and resource reserves for the sustainable development of shale gas in China.
{"title":"Geological characteristics, resource potential, and development direction of shale gas in China","authors":"Xusheng GUO , Ruyue WANG , Baojian SHEN , Guanping WANG , Chengxiang WAN , Qianru WANG","doi":"10.1016/S1876-3804(25)60002-4","DOIUrl":"10.1016/S1876-3804(25)60002-4","url":null,"abstract":"<div><div>By reviewing the research progress and exploration practices of shale gas geology in China, analyzing and summarizing the geological characteristics, enrichment laws, and resource potential of different types of shale gas, the following understandings have been obtained: (1) Marine, transitional, and lacustrine shales in China are distributed from old to new in geological age, and the complexity of tectonic reworking and hydrocarbon generation evolution processes gradually decreases. (2) The sedimentary environment controls the type of source-reservoir configuration, which is the basis of “hydrocarbon generation and reservoir formation”. The types of source-reservoir configuration in marine and lacustrine shales are mainly source-reservoir integration, with occasional source-reservoir separation. The configuration types of transitional shale are mainly source-reservoir integration and source-reservoir symbiosis. (3) The resistance of rigid minerals to compression for pore preservation and the overpressure facilitate the enrichment of source-reservoir integrated shale gas. Good source reservoir coupling and preservation conditions are crucial for the shale gas enrichment of source-reservoir symbiosis and source-reservoir separation types. (4) Marine shale remains the main battlefield for increasing shale gas reserves and production in China, while transitional and lacustrine shales are expected to become important replacement areas. It is recommended to carry out the shale gas exploration at three levels: Accelerate the exploration of Silurian, Cambrian, and Permian marine shales in the Upper-Middle Yangtze region; make key exploration breakthroughs in ultra-deep marine shales of the Upper-Middle Yangtze region, the new Ordovician marine shale strata in the North China region, the transitional shales of the Carboniferous and Permian, as well as the Mesozoic lacustrine shale gas in basins such as Sichuan, Ordos and Songliao; explore and prepare for new shale gas exploration areas such as South China and Northwest China, providing technology and resource reserves for the sustainable development of shale gas in China.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 17-32"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60004-8
Changgui XU , Keqiang WU , Jianxiang PEI , Lin HU
Based on petroleum exploration and new progress of oil and gas geology study in the Qiongdongnan Basin, combined with seismic, logging, drilling, core, sidewall coring, geochemistry data, a systematic study is conducted on the source, reservoir-cap conditions, trap types, migration and accumulation characteristics, enrichment mechanisms, and reservoir formation models of ultra-deep water and ultra-shallow natural gas, taking the Lingshui 36-1 gas field as an example. (1) The genetic types of the ultra-deep water and ultra-shallow natural gas in the Qiongdongnan Basin include thermogenic gas and biogenic gas, and dominated by thermogenic gas. (2) The reservoirs are mainly composed of the Quaternary deep-water submarine fan sandstone. (3) The types of cap rocks include deep-sea mudstone, mass transport deposits mudstone, and hydrate-bearing formations. (4) The types of traps are mainly lithological, and also include structural- lithological traps. (5) The migration channels include vertical transport channels such as faults, gas chimneys, fracture zones, and lateral transport layers such as large sand bodies and unconformity surfaces, forming a single or composite transport framework. A new natural gas accumulation model is proposed for ultra-deep water and ultra-shallow layers, that is, dual source hydrocarbon supply, gas chimney and submarine fan composite migration, deep-sea mudstone-mass transport deposits mudstone-hydrate-bearing strata ternary sealing, late dynamic accumulation, and large-scale enrichment at ridges. The new understanding obtained from the research has reference and enlightening significance for the next step of deepwater and ultra-shallow layers, as well as oil and gas exploration in related fields or regions.
{"title":"Enrichment mechanisms and accumulation model of ultra-deep water and ultra-shallow gas: A case study of Lingshui 36-1 gas field in Qiongdongnan Basin, South China Sea","authors":"Changgui XU , Keqiang WU , Jianxiang PEI , Lin HU","doi":"10.1016/S1876-3804(25)60004-8","DOIUrl":"10.1016/S1876-3804(25)60004-8","url":null,"abstract":"<div><div>Based on petroleum exploration and new progress of oil and gas geology study in the Qiongdongnan Basin, combined with seismic, logging, drilling, core, sidewall coring, geochemistry data, a systematic study is conducted on the source, reservoir-cap conditions, trap types, migration and accumulation characteristics, enrichment mechanisms, and reservoir formation models of ultra-deep water and ultra-shallow natural gas, taking the Lingshui 36-1 gas field as an example. (1) The genetic types of the ultra-deep water and ultra-shallow natural gas in the Qiongdongnan Basin include thermogenic gas and biogenic gas, and dominated by thermogenic gas. (2) The reservoirs are mainly composed of the Quaternary deep-water submarine fan sandstone. (3) The types of cap rocks include deep-sea mudstone, mass transport deposits mudstone, and hydrate-bearing formations. (4) The types of traps are mainly lithological, and also include structural- lithological traps. (5) The migration channels include vertical transport channels such as faults, gas chimneys, fracture zones, and lateral transport layers such as large sand bodies and unconformity surfaces, forming a single or composite transport framework. A new natural gas accumulation model is proposed for ultra-deep water and ultra-shallow layers, that is, dual source hydrocarbon supply, gas chimney and submarine fan composite migration, deep-sea mudstone-mass transport deposits mudstone-hydrate-bearing strata ternary sealing, late dynamic accumulation, and large-scale enrichment at ridges. The new understanding obtained from the research has reference and enlightening significance for the next step of deepwater and ultra-shallow layers, as well as oil and gas exploration in related fields or regions.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 50-63"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464686","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60011-5
Yan JIN , Botao LIN , Yanfang GAO , Huiwen PANG , Xuyang GUO , Junjie SHENTU
Considering the three typical phase-change related rock mechanics phenomena during drilling and production in oil and gas reservoirs, which include phase change of solid alkane-related mixtures upon heating, sand liquefaction induced by sudden pressure release of the over-pressured sand body, and formation collapse due to gasification of pore fillings from pressure reduction, this study first systematically analyzes the progress of theoretical understanding, experimental methods, and mathematical representation, then discusses the engineering application scenarios corresponding to the three phenomena and reveals the mechanical principles and application effectiveness. Based on these research efforts, the study further discusses the significant challenges, potential developmental trends, and research approaches that require urgent exploration. The findings disclose that various phase-related rock mechanics phenomena require specific experimental and mathematical methods that can produce multi-field coupling mechanical mechanisms, which will eventually instruct the control on resource exploitation, evaluation on disaster level, and analysis of formation stability. To meet the development needs of the principle, future research efforts should focus on mining more phase-change related rock mechanics phenomena during oil and gas resources exploitation, developing novel experimental equipment, and using techniques of artificial intelligence and digital twins to implement real-time simulation and dynamic visualization of phase-change related rock mechanics.
{"title":"Theories and applications of phase-change related rock mechanics in oil and gas reservoirs","authors":"Yan JIN , Botao LIN , Yanfang GAO , Huiwen PANG , Xuyang GUO , Junjie SHENTU","doi":"10.1016/S1876-3804(25)60011-5","DOIUrl":"10.1016/S1876-3804(25)60011-5","url":null,"abstract":"<div><div>Considering the three typical phase-change related rock mechanics phenomena during drilling and production in oil and gas reservoirs, which include phase change of solid alkane-related mixtures upon heating, sand liquefaction induced by sudden pressure release of the over-pressured sand body, and formation collapse due to gasification of pore fillings from pressure reduction, this study first systematically analyzes the progress of theoretical understanding, experimental methods, and mathematical representation, then discusses the engineering application scenarios corresponding to the three phenomena and reveals the mechanical principles and application effectiveness. Based on these research efforts, the study further discusses the significant challenges, potential developmental trends, and research approaches that require urgent exploration. The findings disclose that various phase-related rock mechanics phenomena require specific experimental and mathematical methods that can produce multi-field coupling mechanical mechanisms, which will eventually instruct the control on resource exploitation, evaluation on disaster level, and analysis of formation stability. To meet the development needs of the principle, future research efforts should focus on mining more phase-change related rock mechanics phenomena during oil and gas resources exploitation, developing novel experimental equipment, and using techniques of artificial intelligence and digital twins to implement real-time simulation and dynamic visualization of phase-change related rock mechanics.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 157-169"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Coal measures are significant hydrocarbon source rocks and reservoirs in petroliferous basins. Many large gas fields and coalbed methane fields globally are originated from coal-measure source rocks or accumulated in coal rocks. Inspired by the discovery of shale oil and gas, and guided by “the overall exploration concept of considering coal rock as reservoir”, breakthroughs in the exploration and development of coal-rock gas have been achieved in deep coal seams with favorable preservation conditions, thereby opening up a new development frontier for the unconventional gas in coal-rock reservoirs. Based on the data from exploration and development practices, a systematic study on the accumulation mechanism of coal-rock gas has been conducted. The mechanisms of “three fields” controlling coal-rock gas accumulation are revealed. It is confirmed that the coal-rock gas is different from CBM in accumulation process. The whole petroleum systems in the Carboniferous–Permian transitional facies coal measures of the eastern margin of the Ordos Basin and in the Jurassic continental facies coal measures of the Junggar Basin are characterized, and the key research directions for further developing the whole petroleum system theory of coal measures are proposed. Coal rocks, compared to shale, possess intense hydrocarbon generation potential, strong adsorption capacity, dual-medium reservoir properties, and partial or weak oil and gas self-sealing capacity. Additionally, unlike other unconventional gas such as shale gas and tight gas, coal-rock gas exhibits more complex accumulation characteristics, and its accumulation requires a certain coal-rock play form lithological and structural traps. Coal-rock gas also has the characteristics of conventional fractured gas reservoirs. Compared with the basic theory and model of the whole petroleum system established based on detrital rock formations, coal measures have distinct characteristics and differences in coal-rock reservoirs and source-reservoir coupling. The whole petroleum system of coal measures is composed of various types of coal-measure hydrocarbon plays with coal (and dark shale) in coal measures as source rock and reservoir, and with adjacent tight layers as reservoirs or cap or transport layers. Under the action of source-reservoir coupling, coal-rock gas is accumulated in coal-rock reservoirs with good preservation conditions, tight oil/gas is accumulated in tight layers, or conventional oil/gas is accumulated in traps far away from sources, and coalbed methane is accumulated in coal-rock reservoirs damaged by later geological processes. The proposed whole petroleum system of coal measures represents a novel type of whole petroleum system.
{"title":"Coal-rock gas accumulation mechanism and the whole petroleum system of coal measures","authors":"Guoxin LI , Chengzao JIA , Qun ZHAO , Tianqi ZHOU , Jinliang GAO","doi":"10.1016/S1876-3804(25)60003-6","DOIUrl":"10.1016/S1876-3804(25)60003-6","url":null,"abstract":"<div><div>Coal measures are significant hydrocarbon source rocks and reservoirs in petroliferous basins. Many large gas fields and coalbed methane fields globally are originated from coal-measure source rocks or accumulated in coal rocks. Inspired by the discovery of shale oil and gas, and guided by “the overall exploration concept of considering coal rock as reservoir”, breakthroughs in the exploration and development of coal-rock gas have been achieved in deep coal seams with favorable preservation conditions, thereby opening up a new development frontier for the unconventional gas in coal-rock reservoirs. Based on the data from exploration and development practices, a systematic study on the accumulation mechanism of coal-rock gas has been conducted. The mechanisms of “three fields” controlling coal-rock gas accumulation are revealed. It is confirmed that the coal-rock gas is different from CBM in accumulation process. The whole petroleum systems in the Carboniferous–Permian transitional facies coal measures of the eastern margin of the Ordos Basin and in the Jurassic continental facies coal measures of the Junggar Basin are characterized, and the key research directions for further developing the whole petroleum system theory of coal measures are proposed. Coal rocks, compared to shale, possess intense hydrocarbon generation potential, strong adsorption capacity, dual-medium reservoir properties, and partial or weak oil and gas self-sealing capacity. Additionally, unlike other unconventional gas such as shale gas and tight gas, coal-rock gas exhibits more complex accumulation characteristics, and its accumulation requires a certain coal-rock play form lithological and structural traps. Coal-rock gas also has the characteristics of conventional fractured gas reservoirs. Compared with the basic theory and model of the whole petroleum system established based on detrital rock formations, coal measures have distinct characteristics and differences in coal-rock reservoirs and source-reservoir coupling. The whole petroleum system of coal measures is composed of various types of coal-measure hydrocarbon plays with coal (and dark shale) in coal measures as source rock and reservoir, and with adjacent tight layers as reservoirs or cap or transport layers. Under the action of source-reservoir coupling, coal-rock gas is accumulated in coal-rock reservoirs with good preservation conditions, tight oil/gas is accumulated in tight layers, or conventional oil/gas is accumulated in traps far away from sources, and coalbed methane is accumulated in coal-rock reservoirs damaged by later geological processes. The proposed whole petroleum system of coal measures represents a novel type of whole petroleum system.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 33-49"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60005-X
Tonglou GUO , Hucheng DENG , Shuang ZHAO , Limin WEI , Jianhua HE
The basic geological characteristics of the Qiongzhusi Formation reservoirs and conditions for shale gas enrichment and high-yield were studied by using methods such as mineral scanning, organic and inorganic geochemistry, breakthrough pressure, and triaxial mechanics testing based on the core, logging, seismic and production data. (1) Both types of silty shale, rich in organic matter in deep water and low in organic matter in shallow water, have good gas bearing properties. (2) The brittle mineral composition of shale is characterized by comparable feldspar and quartz content. (3) The pores are mainly inorganic pores with a small amount of organic pores. Pore development primarily hinges on a synergy between felsic minerals and total organic carbon content (TOC). (4) Dominated by Type I organic matters, the hydrocarbon generating organisms are algae and acritarch, with high maturity and high hydrocarbon generation potential. (5) Deep- and shallow-water shale gas exhibit in-situ and mixed gas generation characteristics, respectively. (6) The basic law of shale gas enrichment in the Qiongzhusi Formation was proposed as “TOC controlled accumulation and inorganic pore controlled enrichment”, which includes the in-situ enrichment model of “three highs and one over” (high TOC, high felsic mineral content, high inorganic pore content, overpressured formation) for organic rich shale represented by Well ZY2, and the in-situ + carrier-bed enrichment model of “two highs, one medium and one low” (high felsic content, high formation pressure, medium inorganic pore content, low TOC) for organic-poor shale gas represented by Well JS103. It is a new type of shale gas that is different from the Longmaxi Formation, enriching the formation mechanism of deep and ultra-deep shale gas. The deployment of multiple exploration wells has achieved significant breakthroughs in shale gas exploration.
{"title":"Formation mechanisms and exploration breakthroughs of new type of shale gas in Cambrian Qiongzhusi Formation, Sichuan Basin, SW China","authors":"Tonglou GUO , Hucheng DENG , Shuang ZHAO , Limin WEI , Jianhua HE","doi":"10.1016/S1876-3804(25)60005-X","DOIUrl":"10.1016/S1876-3804(25)60005-X","url":null,"abstract":"<div><div>The basic geological characteristics of the Qiongzhusi Formation reservoirs and conditions for shale gas enrichment and high-yield were studied by using methods such as mineral scanning, organic and inorganic geochemistry, breakthrough pressure, and triaxial mechanics testing based on the core, logging, seismic and production data. (1) Both types of silty shale, rich in organic matter in deep water and low in organic matter in shallow water, have good gas bearing properties. (2) The brittle mineral composition of shale is characterized by comparable feldspar and quartz content. (3) The pores are mainly inorganic pores with a small amount of organic pores. Pore development primarily hinges on a synergy between felsic minerals and total organic carbon content (TOC). (4) Dominated by Type I organic matters, the hydrocarbon generating organisms are algae and acritarch, with high maturity and high hydrocarbon generation potential. (5) Deep- and shallow-water shale gas exhibit in-situ and mixed gas generation characteristics, respectively. (6) The basic law of shale gas enrichment in the Qiongzhusi Formation was proposed as “TOC controlled accumulation and inorganic pore controlled enrichment”, which includes the in-situ enrichment model of “three highs and one over” (high TOC, high felsic mineral content, high inorganic pore content, overpressured formation) for organic rich shale represented by Well ZY2, and the in-situ + carrier-bed enrichment model of “two highs, one medium and one low” (high felsic content, high formation pressure, medium inorganic pore content, low TOC) for organic-poor shale gas represented by Well JS103. It is a new type of shale gas that is different from the Longmaxi Formation, enriching the formation mechanism of deep and ultra-deep shale gas. The deployment of multiple exploration wells has achieved significant breakthroughs in shale gas exploration.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 64-78"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464687","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60015-2
Lijun YOU, Rui QIAN, Yili KANG, Yijun WANG
Static adsorption and dynamic damage experiments were carried out on typical 8# deep coal rock of the Carboniferous Benxi Formation in the Ordos Basin, NW China, to evaluate the adsorption capacity of hydroxypropyl guar gum and polyacrylamide as fracturing fluid thickeners on deep coal rock surface and the permeability damage caused by adsorption. The adsorption morphology of the thickener was quantitatively characterized by atomic force microscopy, and the main controlling factors of the thickener adsorption were analyzed. Meanwhile, the adsorption mechanism of the thickener was revealed by Zeta potential, Fourier infrared spectroscopy and X-ray photoelectron spectroscopy. The results show that the adsorption capacity of hydroxypropyl guar gum on deep coal surface is 3.86 mg/g, and the permeability of coal rock after adsorption decreases by 35.24%–37.01%. The adsorption capacity of polyacrylamide is 3.29 mg/g, and the permeability of coal rock after adsorption decreases by 14.31%–21.93%. The thickness of the thickener adsorption layer is positively correlated with the mass fraction of thickener and negatively correlated with temperature, and a decrease in pH will reduce the thickness of the hydroxypropyl guar gum adsorption layer and make the distribution frequency of the thickness of polyacrylamide adsorption layer more concentrated. Functional group condensation and intermolecular force are chemical and physical forces for adsorbing fracturing fluid thickener in deep coal rock. Optimization of thickener mass fraction, chemical modification of thickener molecular, oxidative thermal degradation of polymer and addition of desorption agent can reduce the potential damages on micro-nano pores and cracks in coal rock.
{"title":"Adsorption damage mechanism and control of fracturing fluid thickener in deep coal rock","authors":"Lijun YOU, Rui QIAN, Yili KANG, Yijun WANG","doi":"10.1016/S1876-3804(25)60015-2","DOIUrl":"10.1016/S1876-3804(25)60015-2","url":null,"abstract":"<div><div>Static adsorption and dynamic damage experiments were carried out on typical 8<sup>#</sup> deep coal rock of the Carboniferous Benxi Formation in the Ordos Basin, NW China, to evaluate the adsorption capacity of hydroxypropyl guar gum and polyacrylamide as fracturing fluid thickeners on deep coal rock surface and the permeability damage caused by adsorption. The adsorption morphology of the thickener was quantitatively characterized by atomic force microscopy, and the main controlling factors of the thickener adsorption were analyzed. Meanwhile, the adsorption mechanism of the thickener was revealed by Zeta potential, Fourier infrared spectroscopy and X-ray photoelectron spectroscopy. The results show that the adsorption capacity of hydroxypropyl guar gum on deep coal surface is 3.86 mg/g, and the permeability of coal rock after adsorption decreases by 35.24%–37.01%. The adsorption capacity of polyacrylamide is 3.29 mg/g, and the permeability of coal rock after adsorption decreases by 14.31%–21.93%. The thickness of the thickener adsorption layer is positively correlated with the mass fraction of thickener and negatively correlated with temperature, and a decrease in pH will reduce the thickness of the hydroxypropyl guar gum adsorption layer and make the distribution frequency of the thickness of polyacrylamide adsorption layer more concentrated. Functional group condensation and intermolecular force are chemical and physical forces for adsorbing fracturing fluid thickener in deep coal rock. Optimization of thickener mass fraction, chemical modification of thickener molecular, oxidative thermal degradation of polymer and addition of desorption agent can reduce the potential damages on micro-nano pores and cracks in coal rock.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 208-218"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/S1876-3804(25)60020-6
Kelu SU , Jiaai ZHONG , Wei WANG , Wenbin SHI , Zuqing CHEN , Yuping LI , Zhiwei FAN , Jianbo WANG , Yong LIU , Bei PAN , Zhicheng LIU , Yanxia JIANG , Zirui LIANG , Yuying ZHANG , Fuming WANG
Wells CXD1 and CX2 have uncovered high-concentration potassium- and lithium- containing brines and substantial layers of halite-type polyhalite potash deposits within the 4th and 5th members of the Triassic Jialingjiang Formation and the 1st Member of Leikoupo Formation (Jia 4 Member, Jia 5 Member, and Lei 1 Member) in the Puguang area, Sichuan Basin. These discoveries mark significant breakthroughs in the exploration of deep marine potassium and lithium resources within the Sichuan Basin. Utilizing the concept of “gas-potassium-lithium integrated exploration” and incorporating drilling, logging, seismic, and geochemical data, we have investigated the geological and enrichment conditions, as well as the metallogenic model of potassium-rich and lithium-rich brines and halite-type polyhalite. First, the sedimentary systems of gypsum-dolomite flats, salt lakes and evaporated flats were developed in Jia 4 Member, Jia 5 Member, and the 1st member of Leikoupo Formation (Lei 1 Member) in northeastern Sichuan Basin, forming three large-scale salt-gathering and potassium formation centers in Puguang, Tongnanba and Yuanba, and developing reservoirs with potassium-rich and lithium-rich brines, which are favorable for the deposition of potassium and lithium resources in both solid or liquid phases. Second, the soluble halite-type polyhalite has a large thickness and wide distribution, and the reservoir brine has a high content of K+ and Li+. A solid-liquid superimposed “three-story structure” (with the lower thin-layer of brine reservoir in lower part of Jia 4 Member and Jia 5 Member, middle layer of halite-type polyhalite potash depositS, upper layer of potassium-rich and lithium-rich brine reservoir in Lei 1 Member) is formed. Third, the ternary enrichment and mineralization patterns for potassium and lithium resources were determined. Vertical superposition of polyhalite and green bean rocks is the mineral material basis of potassium-lithium resources featuring “dual-source replenishment and proximal-source release”, with primary seawater and gypsum dehydration as the main sources of deep brines, while multi-stage tectonic modification is the key to the enrichment of halite-type polyhalite and potassium- lithium brines. Fourth, the ore-forming process has gone through four stages: salt-gathering and potassium-lithium accumulation period, initial water-rock reaction period, transformation and aggregation period, and enrichment and finalization period. During this process, the halite-type polyhalite layer in Jia 4 Member and Jia 5 Member is the main target for potassium solution mining, while the brine layer in Lei 1 Member is the focus of comprehensive potassium-lithium exploration and development.
{"title":"Enrichment conditions and metallogenic model of potassium and lithium resources in the Lower–Middle Triassic, northeastern Sichuan Basin, SW China","authors":"Kelu SU , Jiaai ZHONG , Wei WANG , Wenbin SHI , Zuqing CHEN , Yuping LI , Zhiwei FAN , Jianbo WANG , Yong LIU , Bei PAN , Zhicheng LIU , Yanxia JIANG , Zirui LIANG , Yuying ZHANG , Fuming WANG","doi":"10.1016/S1876-3804(25)60020-6","DOIUrl":"10.1016/S1876-3804(25)60020-6","url":null,"abstract":"<div><div>Wells CXD1 and CX2 have uncovered high-concentration potassium- and lithium- containing brines and substantial layers of halite-type polyhalite potash deposits within the 4th and 5th members of the Triassic Jialingjiang Formation and the 1st Member of Leikoupo Formation (Jia 4 Member, Jia 5 Member, and Lei 1 Member) in the Puguang area, Sichuan Basin. These discoveries mark significant breakthroughs in the exploration of deep marine potassium and lithium resources within the Sichuan Basin. Utilizing the concept of “gas-potassium-lithium integrated exploration” and incorporating drilling, logging, seismic, and geochemical data, we have investigated the geological and enrichment conditions, as well as the metallogenic model of potassium-rich and lithium-rich brines and halite-type polyhalite. First, the sedimentary systems of gypsum-dolomite flats, salt lakes and evaporated flats were developed in Jia 4 Member, Jia 5 Member, and the 1st member of Leikoupo Formation (Lei 1 Member) in northeastern Sichuan Basin, forming three large-scale salt-gathering and potassium formation centers in Puguang, Tongnanba and Yuanba, and developing reservoirs with potassium-rich and lithium-rich brines, which are favorable for the deposition of potassium and lithium resources in both solid or liquid phases. Second, the soluble halite-type polyhalite has a large thickness and wide distribution, and the reservoir brine has a high content of K<sup>+</sup> and Li<sup>+</sup>. A solid-liquid superimposed “three-story structure” (with the lower thin-layer of brine reservoir in lower part of Jia 4 Member and Jia 5 Member, middle layer of halite-type polyhalite potash depositS, upper layer of potassium-rich and lithium-rich brine reservoir in Lei 1 Member) is formed. Third, the ternary enrichment and mineralization patterns for potassium and lithium resources were determined. Vertical superposition of polyhalite and green bean rocks is the mineral material basis of potassium-lithium resources featuring “dual-source replenishment and proximal-source release”, with primary seawater and gypsum dehydration as the main sources of deep brines, while multi-stage tectonic modification is the key to the enrichment of halite-type polyhalite and potassium- lithium brines. Fourth, the ore-forming process has gone through four stages: salt-gathering and potassium-lithium accumulation period, initial water-rock reaction period, transformation and aggregation period, and enrichment and finalization period. During this process, the halite-type polyhalite layer in Jia 4 Member and Jia 5 Member is the main target for potassium solution mining, while the brine layer in Lei 1 Member is the focus of comprehensive potassium-lithium exploration and development.</div></div>","PeriodicalId":67426,"journal":{"name":"Petroleum Exploration and Development","volume":"52 1","pages":"Pages 272-284"},"PeriodicalIF":7.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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