| The tectonic effect not only controls the sedimentation and construction process of the oil and gas basin,but also controls the reservoir transformation process in the later stage of hydrocarbon generation.In this paper,the organic-rich shale of the Longmaxi Formation in the Shiliutu Group was studied.Field investigations,experimental tests,numerical simulations,and theoretical studies were used to systematically study the shale gas accumulation characteristics under structural control as scientific issues.Mainly achieved the following understanding and results:The Longmaxi Formation is widely distributed in the study area.Based on field geological surveys and data collection,combined with microstructure,rock fabric analysis,and elemental geochemical characteristics,the ancient sedimentary-tectonic environment,tectonic development,evolutionary processes,stress-strain environment and dynamics experienced in the south of Sichuan were discriminated.It is identified that the pore type of the Longmaxi shale includes organic pores,intergranular pores,intragranular pores,and microfractures.The pore size distribution of the shale is stable.The contribution of pores with a pore diameter of less than 300 nm to the total pore volume of the shale is 83.44%-94.23%.Combined with the fractal dimension calculation model of FHH,the pore specific surface area and pore volume evolved with the maturity of organic matter.Based on the recovery results of single-well sedimentary buried evolutionary history,the characteristics of pore pore volume and specific surface area during the evolution of organic matter were elucidated,and the shale deposits in the Longmaxi Formation in southern Sichuan were classified into four stages of evolution: the rapid burial stage in the late Caledonian period.(About 443Ma-400Ma),the slow uplift phase of the Hercynian phase(western)(About 400Ma-270Ma),the rapid burial phase(About 270Ma-110Ma)of the Indosinian to early Yanshanian period,and the late YanshanianHimalayan period Lifting stage(About 110Ma-10Ma).The Triassic Jialingjiang Formation or Leikoupo Formation in the south of Sichuan Province is the regional overburden of the Longmaxi Formation,LM5-LM6 is the direct overburden of the Longmaxi Formation,and the WF2-LM4 is the main gasbearing formation of the Longmaxi Formation.Based on the reservoir breakthrough experiment and the methane diffusion coefficient experiment,the characteristics of methane diffusion in the reservoir were obtained,and the shale gas formation status was characterized based on the LF model.The shale gas adsorption state was mainly observed.The free gas-based critical conversion depth is between 1300-4900 m.The temperature and pressure changes of shale gas reservoirs are controlled mainly by tectonic actions.Based on energy dynamic equilibrium theory,the shale gas energy evolution and response mechanisms under structural control are clarified,revealing the prolonged tectonic uplift of the study area after the late Yanshanian period.The energy responds positively to changes in the temperature and pressure environment of the reservoir,and the decay rate of the elastic energy of the reservoir block is slower than the decay rate of the gas elastic energy,which is conducive to the process of reservoir porosity rebound and gas occurrence state adjustment;the rate of decay of free gas elastic energy is higher than that of adsorption The rate of decay of aeroelastic energy is fast,and the free state gradually shifts to the adsorption state.Finally,the characteristics of shale gas accumulation under structural control in the south of Sichuan are deeply revealed,and comprehensive analysis and delineation of favorable areas and favorable areas for shale gas exploration and development in the study area. |
PDF Full Text Request