Study On Factors Affecting Volumetric Fracturing Capacity Of Shale Gas Reservoirs

Volume fracturing is the most effective fracturing measure for development of shale gas reservoir, it can create complex fracture network in reservoir and communicate with micro fractures, which can provide efficient flow path for gas of the reservoir. In order to exploit shale gas reservoir efficiently by volume fractured horizontal well, one of the conditions is to fully understand the flow mechanisms of shale gas in the reservoir, another is to describe the complex fracture network which produced by volume fracturing. Therefore, solving the two questions is the necessary foundation for analyzing affecting factor of productivity of volume fractured shale gas reservoir.After recognizing the storage and migration mechanisms, On the basis of considering desorption, Knudsen diffusion and slippage effect in matrix pores, models of a shale gas volume fractured horizontal well were established. Numerical simulation software which called Eclipse was applied to simulate the complex fracture network, on the basis of that, production performance of horizontal well of shale gas are simulated and analyzed. Several sensitivity analysis are done to understand the effect of reservoir parameters and volume fracturing parameters to the productivity of shale gas well. Then the important order of affecting factors of shale gas well productivity are determined by orthogonal analysis. Following conclusions are made through above research:(1) The state of gas stored in the shale gas reservoir and migration mechanism of it are recognized through literature research, apparent permeability model was established on the base of considering Knudsen diffusion and slippage effect, and the relationship between the apparent permeability coefficient and pressure.(2) The tri-linear flow models of volume fracturing horizontal well in shale gas reservoir was established, then the solutions of model were derived, the corresponding curves of production of bounded shale gas reservoir were got by Stehfest. On the basis of that, flow processes were divided and the parameters like apparent permeability coefficient, desorption factor, interporosity flow coefficient, storativity ratio, conductivity of fractures, half-distance between hydraulic fractures were analyzed.(3) A volume fracturing horizontal well model of shale gas reservoir was established in Eclipse, complex fracture networks in the volume fractured formation were simulated by control grid size. Slippage effect in favor of production in middle and late periods of shale gas well; Rock compressibility, Langmuir pressure, Langmuir volume are weak sensitive to productivity; interporosity flow coefficient, gas diffusion coefficient and adsorbed gas content are medium sensitive to productivity; Permeability of natural fractures, conductivity of hydraulic fracture network, stimulated reservoir volume (SRV) are extremely sensitive to productivity.(4) It was found that SRV is the key factor affecting productivity of volume fractured shale gas reservoir by orthogonal analysis. In actual development of shale gas reservoir, SRV should be great as much as possible to enhance the recovery of reservoir.