Study On Mechanism And Characteristics Of Low Velocity Seepage In Ultra-low Permeability Sandstone Gas Reservoirs

Porous medium seepage at low speed whetherconforming for the Darcy linear flow is a hot topic in the academic circles debate, scholars in order to solve this problem from different angles has carried on the related research but does not appear to agree on a conclusion. Some view Newtonian fluid flow in any space in accord with Darcy flow, the experimental test of the low-speed non-Darcy phenomenon caused by technical constraints for the test method or test experiment illusion; Some view, space scale smaller flow in the porous medium due to reasons such as the boundary layer effect, Jamin effect of porous media fluid conductivity changes, resulting in a deviation from Darcy linear flow law. Understand law of fluid flow in the porous media evaluation and calculation of gas reservoir engineering theory, gas reservoirs to improve recovery efficiency measures and the preparation of development plan is of great significance, so in this paper, the fluid under different conditions of flow rule and characteristics of exploratory research, in order to further know low-speed fluid in porous media seepage rule to provide the reference.This paper adopts the seepage experiment and theoretical analysis of a combination of analysis of porous media seepage problem at low speed. Experimental part of the core of low permeability sandstone gas single-phase, saturated oil and water seepage experiment, different flow conditions, such as ultra-low permeability sandstone gas reservoir flow rate and pressure difference relationship, analysis of the experimental results of different fluids in porous media seepage low-speed non-Darcy flow characteristics; For different types of capillary two phase flow types are analyzed in theory, has carried on the related to micro two-phase fluid flow; For low-speed non-Darcy flow conditions and the size of deviation degree of Darcy flow problem, adopted a more leading edge digital core technology was analyzed, derive the single-phase compressible fluid, gas water two phase flow theory of random pore network model, the independent writing single-phase compressible fluid and gas water two phase flow algorithm and better simulate experiments in low permeability sandstone extracting vacuum, water saturation, water phase displacement and the process of establishing bound water, meticulous to simulate the dynamic process of gas pressure drop in the process of pumping air into vacuum state, saturated water in the process of gas occurrence state, residual gas phase distribution and the change of the total water saturation, and, in the process of water displacement, and the gas volume expansion as the pore pressure decreases in the circle of gas flow process, simulate the seepage experiment and the corresponding displacement curve, analyzes the different experimental time gas phase and water phase saturation distribution and flow characteristics, find out the two phase flow in the process of displaced along the displacement process by flow to change rule. Combining process simulation results and experimental data, the paper puts forward the conclusion that Newton fluid flow does not produce real porous media TPG and low-speed non-Darcy flow and multiphase flow when the liquid boundary layer and the effective stress change is closely related to the factors.