The Research On Unsteady-State Method Of Fluid Flow Through Shale Gas Reservoir

Shale gas is abundant in China. According to the statistical data of EIA, China has a shale gas resource quantity of approximately 1.344×1015m3. But the technical recoverable reserves, however, are evaluated to be around 3.15×1014m3. In addition,the shale gas reserves evaluation of China presented by different experts and scholars varies exceedingly, which mainly results from the inaccuracy of the test of shale gas porosity and permeability data. Hence, it is necessary to develop the determination method of permeability further. Based on the proficiency in shale gas reservoir characteristics, seepage mathematical models of conventional cores, fractured cores and shale cores were developed, and pressure response solutions of upstream chamber and downstream chamber were acquired. Using VC++6.0 to solve the pressure response solutions, the semi-log plot of dimensionless pseudo pressure and time is obtained, and then effects on the pressure response plot caused by every parameter were analyzed. On this basis, shale gas porosity and permeability experiment process and interpretation method were developed. Main research results obtained in this paper are as follows:(1)Based on a large number of literature review, shale gas geologic characteristics and occurrence mechanisms were analyzed and concluded, which laid a physical foundation for shale core adsorption-diffusion-seepage mathematical model.(2)According to fundamental principle of fluid mechanics in porous medium,conventional core seepage mathematical model were developed. By Laplace transform, pressure response mathematical model of upstream chamber and downstream chamber were acquired. Hereby, impacts on pressure response characteristics of upstream chamber and downstream chamber exerted by parameters such as matrix porosity, matrix permeability, fracture porosity, fracture permeability and so on were analyzed.(3)According to fundamental principle of fluid mechanics in porous medium,fractured core seepage mathematical model were developed. By Laplace transform,pressure response mathematical model of upstream chamber and downstream chamber were acquired. Hereby, impacts on pressure response characteristics of upstream chamber and downstream chamber exerted by parameters such as matrix porosity, matrix permeability, fracture porosity, fracture permeability and so on were analyzed.(4)On the basis of Langmuir Adsorption Isotherm, Fick’s Second Law of Diffusion, Darcy’s law of seepage, according to fundamental principle of fluidmechanics in porous medium, a mathematical model of seepage in dual-porosity and single-permeability shale gas core while considering matrix diffusion and microfracture seepage. By Laplace transform, pressure response mathematical model of upstream chamber and downstream chamber were acquired. And impacts on pressure response characteristics of upstream chamber and downstream chamber exerted by factors such as matrix storativity ratio, Langmuir parameters, diffusion coefficient and so on were analyzed.(5)Based on the theoretical study on unstable testing of seepage capability, shale seepage experiment process of unstable testing was designed, and interpretation method of laboratory data was developed. Physical property tests on shale cores were conducted, which has validated the reliability of the theoretical study.