致密气自扩散渗流模型

Tight gas reservoirs have begun to be exploitated on a large scale in the world, of which the basic flow mechanism is still unclear. It is difficult to perfectly interpret production data using the existing flow models. Through the comparison of actual cases, this paper introduces and explores the new flow model proposed by Jin and Chen (2019)and its applicability by examples. According to the N-S equation of compressible fluids and based on the theory of Klainerman and Majda (1982)for low Mach number flow, Jin and Chen obtained the new flow equation for the primary recovery of tight gas reservoirs on the reservoir scale in the case of time scale greater than the acoustic time scale using asymptotic expansion, multi-scale analysis and the upscaling technique of volume averaging. The new flow equation reflects the physical nature that the primary recovery of tight gas reservoirs is driven entirely by the expansibility of gas, and its diffusion coefficient is proportional to porosity and gas viscosity, and inversely proportional to gas density. The comparison by case studies between the self-diffusion model and the current flow model based on the Darcy's law and its modification shows that the gas yield obtained by the Darcy and combined flow model can only be consistent with the actual production data when the producing pressure drop is small, and the gas yield at this time is small; the larger the producing pressure drop, the greater the deviation between the Darcy flow model and the actual production data; the gas yield calculated by the self-diffusion model can well fit the actual production data.