Study On Calculation Method Of Shale Gas Reservoir Reserves And Numerical Simulation Under Fluid-solid Coupling

The influence of the volume of the adsorption gas on the porosity is not considered in the calculation of the geological reserve of the shale gas reservoir by the conventional volume method,so the calculation result is too large,and the organic carbon content and the nano-pore percentage have an important influence on the calculation of the shale gas reserves.Therefore,the reserves of the shale gas reservoir are calculated and these factors should be fully taken into account.Because of the deformation of the rock skeleton,the physical parameters of the shale reservoir,in particular the porosity and the permeability,are changed,and then the flow of the fluid is affected.Therefore,it is necessary to consider the effect of the stress field and the fluid-solid coupling on the seepage.Taking the volume method as the starting point,this paper calculates the geological reserves and calculates the reserves by using petrel software.On this basis,considering the molecular volume of shale gas adsorption and modifying porosity,the geological reserves are calculated and compared with the traditional methods.then,the stress field control equation of the shale reservoir is derived based on the constitutive equation,the double-medium gas-water discrete fracture network model of the shale gas reservoir is derived based on the seepage theory and the material balance equation and the Langmuir adsorption isothermal type,and the matrix-fracture channeling equation is The dynamic model of reservoir physical parameters is derived based on the theory of elastic deformation of porous media.Based on the above equations,a mathematical equation for gas-water-water-solid coupling of shale gas is set up,and the model is solved by comsol,and the following conclusions are obtained:(1)Based on the calculation method of the traditional shale gas reserves,a method of correcting porosity is proposed to calculate the free gas reserves from a single adsorption gas molecule,considering the adsorption gas volume and the organic carbon content.(2)Through the analysis of single well discrete fracture fluid-solid coupling model,the results show that with the increase of production time,the range of pressure change becomes larger;In the region where natural fracture and artificial fracture are connected,the gas pressure decreases most sharply,but the gas pressure of natural fracture which is not connected with fracturing fracture is higher,and the decrease of porosity and permeability caused by coupling will lead to the obvious decrease of production.(3)The results show that the cumulative output of single well is high when the gas pressure is high,and the cumulative output will be overestimated to a certain extent without considering the deformation of the pore medium.The results show that,when the carbon content is high,the cumulative output of the single well is improved by comparing the cumulative output of the single well with the carbon content in the coupling model and the non-coupling model,and the cumulative output of the single well is lower when the deformation of the pore medium is taken into account;in the coupled model,The results show that the higher the crustal stress,the lower the single well output.(4)The results show that the pressure distribution is not uniform across the whole block,the pressure drop in the horizontal well bore and the artificial fracture is fast,the natural fracture which is not in communication with the artificial fracture,and the pressure drop is not obvious or even higher.The results show that the pressure gradient of the well bore and the gas reservoir decreases with the increase of the production time,and the pressure gradient in the well bore and the gas reservoir decreases with the increase of production time.The production rate is reduced.(5)By comparing the block coupling model with the uncoupled model,the pressure drop is slower,the porosity and permeability are lower,and the gas saturation near the wellbore is higher under the same mining time.At the same time,under the condition of coupling,the higher the pressure of shale gas reservoir,the higher the cumulative production of the block;the higher the carbon content,the higher the output;the higher the in-situ stress,the lower the cumulative production;the higher the carbon content is,the higher the output is;the higher the in-situ stress is,the lower the cumulative production is.