The marine–continental transitional shale (MCTS) reservoirs of the Longtan Formation (LTF) are widely distributed in the Sichuan Basin. However, the LTF shale exhibits considerable variations in mineral composition a...The marine–continental transitional shale (MCTS) reservoirs of the Longtan Formation (LTF) are widely distributed in the Sichuan Basin. However, the LTF shale exhibits considerable variations in mineral composition and pore characteristics, which makes identifying the 'sweet spot'a challenging task. To address this issue, 10 samples from four typical shale gas wells in the LTF in the southern Sichuan Basin were selected and analyzed for total organic carbon (TOC) content, whole-rock composition using X-ray diffraction (XRD), low-pressure gas adsorption, and high-pressure mercury intrusion. The lithofacies distribution and pore structure of the MCTS were studied to determine the pore structural characteristics and the primary factors influencing pore formation in different types of shale lithofacies in the LTF. The lithofacies of the LTF shale in the study area can be classified into three categories: siliceous clay shale, clay shale and mixed shale. Mineral content has a significant impact on the pore characteristics, while TOC content has a minor effect on the pore volume and specific surface area of micropores and mesopores. It can be inferred that the mesopores in the MCTS are mainly related to clay mineral pores, and mineral dissolution and TOC content are not the primary factors contributing to pore formation.展开更多
As a typical kind of lithologic reservoirs,reef reservoirs are generally featured by their large single-well reservoir thickness,good reservoir physical properties,and high gas well productivity.The Upper Permian Chan...As a typical kind of lithologic reservoirs,reef reservoirs are generally featured by their large single-well reservoir thickness,good reservoir physical properties,and high gas well productivity.The Upper Permian Changxing Formation is an important natural gas exploration target in the Sichuan Basin,which hosts a large reef gas reservoir and is mainly distributed along the Kaijiang-Liangping Trough.Comprehensive analyses are implemented to investigate reservoir characteristics and identify controlling factors of reef reservoirs in Changxing Formation in the Eastern Longgang Area,Northeastern Sichuan Basin,including core,logging,and seismic data analyses.Changxing Formation reservoirs in the study area mainly occur in the reef-shoal complex,which are featured by wide distribution,large thickness and generally good physical properties.Reservoir rocks are dominantly composed of bioclastic dolomite and silty-fine dolomite(with grain phantom structure),while the main reservoir space consists of residual intergranular pores,intergranular dissolution pores,and karst vugs.In the seismic profiles,typical mound-shaped chaotic reflections can be clearly seen.It is suggested by the main reservoir development controlling factor analysis that the distributions of reef reservoirs are typically controlled by sedimentary facies belts,while the scale of the reef-shoal complex is determined by the pene-sedimentary micro-paleo-geomorphology.Dolomitization can not only significantly preserve the primary pores but also enhance the permeability of rocks.Moreover,karstification is the key to high-quality reef-shoal reservoirs.展开更多
基金supported by the National Natural Science Foundation of China(NNSFC)(Grant No.42272184)2022 Research Program of PetroChina Southwest Oil and Gas Field Company(2022JS-1809).
文摘The marine–continental transitional shale (MCTS) reservoirs of the Longtan Formation (LTF) are widely distributed in the Sichuan Basin. However, the LTF shale exhibits considerable variations in mineral composition and pore characteristics, which makes identifying the 'sweet spot'a challenging task. To address this issue, 10 samples from four typical shale gas wells in the LTF in the southern Sichuan Basin were selected and analyzed for total organic carbon (TOC) content, whole-rock composition using X-ray diffraction (XRD), low-pressure gas adsorption, and high-pressure mercury intrusion. The lithofacies distribution and pore structure of the MCTS were studied to determine the pore structural characteristics and the primary factors influencing pore formation in different types of shale lithofacies in the LTF. The lithofacies of the LTF shale in the study area can be classified into three categories: siliceous clay shale, clay shale and mixed shale. Mineral content has a significant impact on the pore characteristics, while TOC content has a minor effect on the pore volume and specific surface area of micropores and mesopores. It can be inferred that the mesopores in the MCTS are mainly related to clay mineral pores, and mineral dissolution and TOC content are not the primary factors contributing to pore formation.
基金The current study is supported by the National Natural Science Foundation of China(41602166)and China Petroleum Science and Technology Innovation Fund Project(2015D-5006-0107).
文摘As a typical kind of lithologic reservoirs,reef reservoirs are generally featured by their large single-well reservoir thickness,good reservoir physical properties,and high gas well productivity.The Upper Permian Changxing Formation is an important natural gas exploration target in the Sichuan Basin,which hosts a large reef gas reservoir and is mainly distributed along the Kaijiang-Liangping Trough.Comprehensive analyses are implemented to investigate reservoir characteristics and identify controlling factors of reef reservoirs in Changxing Formation in the Eastern Longgang Area,Northeastern Sichuan Basin,including core,logging,and seismic data analyses.Changxing Formation reservoirs in the study area mainly occur in the reef-shoal complex,which are featured by wide distribution,large thickness and generally good physical properties.Reservoir rocks are dominantly composed of bioclastic dolomite and silty-fine dolomite(with grain phantom structure),while the main reservoir space consists of residual intergranular pores,intergranular dissolution pores,and karst vugs.In the seismic profiles,typical mound-shaped chaotic reflections can be clearly seen.It is suggested by the main reservoir development controlling factor analysis that the distributions of reef reservoirs are typically controlled by sedimentary facies belts,while the scale of the reef-shoal complex is determined by the pene-sedimentary micro-paleo-geomorphology.Dolomitization can not only significantly preserve the primary pores but also enhance the permeability of rocks.Moreover,karstification is the key to high-quality reef-shoal reservoirs.
