Study On The Flow Model Of Shale Gas Reservoir Considering Rock Deformation

Shale gas is an important unconventional energy source in China.The tremendous changes of formation pressure during its development often lead to the deformation of shale rocks.It is found that fluid flow is assumed to be single-phase flow in flow models considering shale deformation at home and abroad.At the same time,when considering the two-phase flow of fluid,many shale flow models also use indoor stress sensitive experiments to make exponential regression to establish the relationship between rock deformation and flow capacity,which is difficult to accurately describe the real situation of rock deformation.Therefore,in order to establish a gas-water two-phase flow model more suitable for shale gas reservoirs,it is necessary to consider the impact of rock deformation.This paper establishes a new model of relationship between rock mechanics parameters of shale matrix fracture and porosity and permeability of matrix fracture.Based on this model,a gas-water two-phase seepage model of horizontal well in shale gas reservoir considering the influence of rock deformation is established.Finally,the model is solved numerically by IMPES method using MATLAB mathematical programming software and combined with formation parameters and production system of Well A in Fuling Shale Gas Field.Well simulation production.The main work and understanding are as follows:(1)Based on the assumption that both matrix and fracture deform at the same time,and considering the dynamic change of Young's modulus of shale,and considering the influence of adsorption and desorption,the constitutive equation of shale and the definition equation of porosity,the relationship between the deformation of shale fracture and matrix and porosity is deduced respectively.(2)Based on the cubic relationship between permeability and porosity of shale matrix,considering the influence of matrix deformation on gas diffusion and slippage,the relationship between matrix deformation and matrix permeability considering the dynamic change of Young's modulus of shale is deduced.At the same time,the relationship between fracture permeability and fracture deformation of coal seam is analogized,and the deformation and stress of shale fracture derived in this paper are used.The relationship between fracture deformation and fracture permeability considering the dynamic change of Young's modulus of shale is deduced.(3)A gas-water two-phase homogeneous and dual-medium percolation model for shale gas reservoirs considering the effect of rock deformation is established.In the model,the effect of rock dynamic deformation on the percolation law of shale gas reservoirs is considered from the point of view of rock mechanics.For the two models,the finite difference method is used to solve the numerical problems and the results of the model are obtained by computer programming.(4)Under the same in-situ stress change,shale fracture is easier to produce rock deformation faster than shale skeleton.Based on the model,the formation parameters of Well A in Fuling Shale Gas Field are simulated.When the bottom hole flowing pressure is fixed at 7MPa for 360 days,the fracture porosity decreases rapidly and the decrease range is 6.38%,while the skeleton porosity decreases slowly by only 1.45%.(5)Rock deformation reduces the gas production capacity of shale gas wells:Based on this model,the formation parameters of Well A in Fuling shale gas field are simulated and the bottom-hole flowing pressure is set at 7 MPa for 3600 days.The results show that the final recovery rate of gas wells is 80.46%when the influence of rock deformation is neglected,while the final recovery rate of gas wells is 74.69%when the influence of rock deformation is considered,which is 5.77%lower than that of the former.(6)Pore modulus of natural fracture has the most obvious influence on gas well productivity,while the influence of shale skeleton modulus,Lan's strain constant and shale rock density is negligible.When the pore modulus of natural fracture is greater than 1 GPa,rock deformation has little effect on gas well productivity;once the pore modulus of natural fracture is less than 1 GPa,gas well productivity will increase with the increase of the pore modulus of natural fracture.