The Study Of Water-oil Displacement Law In Extra-low Permeability Reservoir

In low permeability oil field of our country, extra-low or ultra-low permeability reservoirs account for more the half, the threshold pressure gradient occurs in extra-low permeability reservoirs and brings difficulties to the oilfield development, at the same time, with the variation of the formation pressure, the formation deformation is usually non-reversible in extra-low permeability reservoirs, It will obviously affect the dynamic characteristics of oilfield. So the flow mechanism research of extra-low permeability reservoir is very important.By developing the connection that permeability varies with the pressure drop in this paper, the non-linear steady flow model is established accounting for non-reversible deformation, and which is sovled with numerical method. Under the condition of constant pressure , the results show that the formation pressure decreases more and more slowly with the permeability drop variation coefficient increasing, the oil production and limit control radius decreases; when the oil production is constant, the formation pressure decreases more and more quickly with the permeability drop variation coefficient increasing; on this basis, the non-linear nonsteady flow model is established accounting for non-reversible deformation, and which is sovled with numerical method, when the oil production is constant, the results show that the formation pressure decreases more and more quickly with the permeability drop variation coefficient increasing, the bottom hole flowing pressure decreases, and limit control radius increases.Based on the treshold pressure gradient study of single phase on extra-low permeability reservoir, we can obtain oil-water two-phase treshold pressure gradient. One-dimension water-oil displacement mathematics model considering threshold pressure gradient is established. By means of numerical solution, computational solution indicates that threshold pressure gradient causes average water saturation rising and formation pressure decreasing; permeability areal heterogeneity causes average water saturation and formation pressure decreasing; on the base of areal heterogeneity dimension is confirmed, when displacing by linear rising mode and firstly rising then decreasing mode, displacement efficiency is better.The one-dimension water-oil displacement and fluid-structure coupling mathematics model is established accounting for deformation characteristic and treshold pressure gradient, and which is sovled with numerical method. Computational solution indicates that porosity and permeability increases under fluid-structure coupling conditions; with respect to non-coupling model, water phase pressure, water saturation and treshold pressure gradient are lower; the formation strain and effective stress increases continuously.