基于有限元法的气藏型储气库双层合采流动模拟

[Objective]Multilayer commingled production is a commonly used method to improve the production efficiency in oil and gas reservoirs with multiple reservoirs having different physical property characteristics. The seepage law of fluids in gas reservoir-type gas storage facilities with highly developed fractures is complex, resulting in an unclear mechanism of commingled production. Moreover, most of the current research on multilayer commingled production of gas reservoirs is carried out at a macroscopic scale. Therefore, using pore-scale flow simulation to study the development mechanism and influencing factors of multilayer commingled production has important practical significance for the design of development plans for gas storage facilities.[Methods] Based on CT scan images, a two-dimensional geometric model for the commingled production of fracture-pore double layers is constructed by combining the microscopic pore-throat structure. Then, the finite element method is used to solve the numerical model of the two-phase flow of the N-S equations to explore the dynamic migration laws of gas and water two-phase fluids during the process of multilayer commingled production. And the effects of double-layer commingled production in gas reservoir-type gas storage facilities with different interlayer heterogeneities are evaluated based on the pore scale.[Results]When the interlayer heterogeneity is weak, the migration of the gas-water interface is relatively uniform, the pressure distribution is stable, the reservoir development is more balanced, and the stable production capacity is improved. When the interlayer heterogeneity is strong, the fluid flows along the high-permeability layer, and crossflow is likely to occur, affecting the development effect. During the process of double-layer commingled production, the production difference between layers gradually decreases and tends to be stable, but it is still affected by heterogeneity. When the heterogeneity is weak, the production of the fracture-pore layer and the pore layer tends to be balanced in the later production period, and the fluid flow is more uniform. The production pressure difference affects the gas well production. When the pressure gradient increases, the proportion of gas production in the pore layer with lower permeability increases, and the overall situation tends to be balanced. Therefore, in the initial production stage, the rate of reservoir pressure reduction should be controlled. In the later stage, the pressure should be appropriately increased or the reservoir energy should be replenished to improve the utilization degree of the low-permeability pore layer, and the pressure gradient should be reasonably controlled to avoid the stress sensitivity phenomenon that affects the productivity.[Conclusion]The above research results emphasize the importance of rationally allocating the development plan in order to make full use of the advantages of different layers in actual gas reservoir-type gas storage facilities when there are significant differences in the physical property characteristics between reservoir layers. At the same time, the strong interlayer heterogeneity caused by the development of large-scale fractures is a key factor affecting the effect of commingled production, which requires accurate identification and the formulation of a reasonable plan in the engineering design. In multilayer commingled production, the interlayer development balance during the production process can be optimized by regulating the production pressure difference, thereby improving the overall recovery rate.