Transient Pressure Analysis And Productivity Prediction For Stress Sensitive Shale Gas Reservoir

Shale gas reservoirs feature many special characteristics,including extremely low porosity and permeability,relatively stronger absorption capacity,gas slippage and diffusion and almost no economic productions.Based on the nature of shale gas and reservoirs where it occurs,this thesis elaborates physical properties and pore space features of shale gas reservoirs,expounds the occurrence of shale gas and the gas absorption and desorption,as well as make clear the overall mechanism of shale gas production.In this connection,Langmiur's law,a well-known principle of isothermal gas absorption,is employed for the regularity of shale gas absorption and desorption in a quantitative description.The first and second Fick's law of gas diffusion is applied for pseudo and transient inter-porosity flow from the matrix system to the fracture system respectively.Fick's basic law of gas diffusion motion(the equation of motion of gas diffusion)and Darcy's law(the equation of motion of gas flow)are used for gas diffusion and flow through porous media in the system where natural micro-fractures develop.Pressuredependent permeability of hydraulic fractures is also taken into account by introducing a permeability modulus and establishing a power-law expression of the permeability.The instantaneous point-source solution to the mathematical model of the shale gas reservoir with infinite boundary is obtained by the method of source function.According to some method of mathematical physics,including the Image Principle and the Superposition Principle,the continuous point-source solution to the mathematical model of the shale gas reservoir with closed top and bottom boundaries and infinite lateral boundary is obtained,and that with all closed boundaries is also achieved.For the longitudinally fractured vertical well and the transversely fractured horizontal well,continuous pressure system and flow flux system at the wall of the hydraulic fracture achieves a successful coupling of gas flow models both in the natural fracture system and the hydraulic fracture.Model verification is conducted by comparing appropriately simplified model in this thesis with the corresponding model in the certain cited references.The self-made computational program successfully realizes the curves of transient pressure behaviors and productivities.On the basis of these curves(pressure derivative curves),flow regimes for both well types are divided and the sensitivity analysis is also demonstrated.Eventually,a field case study for the transversely fractured horizontal well is performed to show the applicability and suitability of the corresponding derived theoretical model.Models in the thesis may play a theoretically guiding role in the flied development of shale gas.