| Our country has abundant deep shale gas resources in the southeast of Sichuan,which is an important development direction for the exploration and exploitation of shale gas.The stress sensitivity of shale reservoir has a very important guiding significance for reservoir development.Previous studies mainly focus on sandstone,carbonate rocks and middle-shallow shale,and little research on deep shale,so it is necessary to study the stress sensitivity of deep shale.The physical characteristics of deep shale of Longmaxi Formation in southern Sichuan are analyzed.It has suitable TOC content and maturity,high temperature,high pressure,fracture development and other characteristics.With the increase of formation depth,the formation pressure coefficient increases gradually,the content of brittle minerals increases,and the porosity decreases.The theoretical models of stress sensitivity of deep shale of Longmaxi Formation in south Sichuan basin considering temperature are established,which are matrix stress sensitivity models respectively.Plate crack stress sensitive model;Matrix-fracture dual pore stress sensitive model.The gas slip-off effect,the influence of temperature on the stress sensitivity and the stress sensitivity hysteresis of deep fractured shale are studied experimentally.The permeability variation during the development process is simulated experimentally,and the theoretical model is verified according to the experimental results.Based on the theoretical model and experimental results,the main influencing factors of stress sensitivity of deep fractured shales of Longmaxi Formation in southern Sichuan are analyzed.Experimental studies show that: for fracture pores,the slippage effect is basically not affected,the results of constant internal pressure experiment and constant confining pressure experiment are basically the same,and the permeability-effective stress curve at the same temperature basically coincides.The influence of temperature on permeability: the natural fracture cores showed a negative exponential decrease;Artificial angled fractures all conform to exponential decline.The permeability of artificially horizontally fractured shale decreases with temperature in the early stage and in the late stage.The recovery degree of shale stress sensitivity decreases with the increase of temperature,the damage degree increases with the increase of temperature,and the stress sensitivity increases with the increase of temperature.When simulating gas field depletion development,permeability decreases exponentially with the increase of effective stress in both natural and artificial fractured cores.The improved exponential model has the best fitting effect,and the power law model can also get a good fitting effect,while the binomial model does not conform to the rule.Pore permeability index,temperature and pore compression coefficient are the main factors affecting the stress sensitivity of deep fractured shales of Longmaxi Formation in southern Sichuan.The rock mechanical properties(elastic modulus,Poisson’s ratio)determine the pore compression coefficient,and the shape,size and number of pores determine the pore-permeability power index.The research results of this paper describe the stress sensitivity law of deep shale gas qualitatively and quantitatively,which has certain guiding significance for the developer of deep shale gas reservoir. |
