Seepage Characteristic Of The Fractured Shale Under Temperature Field-stress Field-seepage Field Multi-Field Coupling

As a new clean energy,shale gas is becoming more and more attractive around the world.Due to shale has the characteristics of low permeability and compact structure,needing to use the stimulation such as hydraulic fracturing to help realize the busness of shale gas mining.Therefore,if shale gas can be high-efficiency exploited will denpend on the understanding and utilization of the seepage characteristics of shale cracks.This thesis takes the fractured shale core from Changning area of Sichuan as research objects,in order to simulate the reservoir environment of different fracture system,Rock shear machine was applied to fracture the shale core.Fractured shale seepage experiment under pore pressure?confining pressure and temperature was carried out by Multi-functional rock triaxial testing machine so as to discuss seepage characteristic of the fractured shale under temperature field-stress field-seepage field multi-field coupling.Meanwhile,in order to explore influence of adsorption properties on seepage characteristic,in the same of experiment condition,the experiments on the permeability of shale He?CH₄ and CO₂ were carried out in this thesis,and their permeability curve was compared and analyzed.Principal results are as follows:?1?Based on the literature research at home and abroad,a detailed analysis was done about structural characteristics of the reservoir in the changning region,longma creek group shale,such as mineral constituent?brittle features?organic matter type?organic content?thermal maturity and pores–fissures feature.According to the result of research,that the mineral composition of the study area is mainly quartz,calcite and clay mineral,high content of brittle mineral and is helpful for later fracturing,the kerogen type are mainly I in the study area,with little type II1,high content of organic matter;The reservoir space is dominated by intergranular pore and tectonic fissure.?2?Three different kinds of fractured shale core seepage experiment of He?CH₄ and CO₂ under pore pressure and confining pressure were carried out by Multi-functional rock triaxial testing machine,the experimental results show that:1)There is a criticle pore pressure in the three gas permeability curves of the fractured shale,which forming reason is related to rock strength?fracture width and pore pressure value;2)There is a cross point in the CO₂ permeability curves for dilatancy of adsorption and skeletal deformation of shale,the more slit width of shale,the more sensitive to the effective stress;3);The stress sensitivity of shale permeability decrease as the pressure increase when the pore pressure remains constant and the permeability is exponentially attenuated with the confining pressure;4)Under the same condition of effective stress,the decrease of the permeability may be related to the adsorption-induced swelling,and the tested permeability relationship of shale under different gases is He>CH₄>CO₂.?3?Temperature seepage experiment was carried out on the basis of normal temperature experiment condition,this thesis explore the effect of temperature on the seepage characteristics of fractured shale,and there are some new discoveries in the experiment:1)Increasing temperature,gas desorption cause permeability increasing for shale matrix shrinkage and widening the flowing channel;2)Under high temperature condition,the fracture structure,mechanical properties and adsorption properties of shale will have changed,which result in change of fractured shale seepage.For exemple,permeability curves of the fractured shale present “negative growth” feature in the stage of high confining pressure;Fractured shale permeability decrease as the temperature increases when the thermal stress is domination,or fractured shale permeability increase as the temperature increases when the adsorption effect is domination.