Calculation Method for Areal Well Pattern Productivity Considering Fracture Directional Pressure-sensitive Effect

Abstract

Given waterflood development characteristics in ultra-low permeability fractured reservoirs, five-spot method, inverted seven-spot method, inverted nine-spot method and rhombic inverted nine-spot areal well pattern productivity calculation methods are derived based on pressure sensitive equation and flow-tube method considering direction of fractures to solve the problem of water injection-induced areal contradiction. Using the actual data of the CQ oilfield, the factors affecting productivity of different well pattern units are analyzed. From the mathematical theory, the calculation problem of areal well pattern productivity considering directional pressure-sensitive effect and starting pressure gradient at the same time is initially solved under the condition of two-phase displacement. The research results show that there is an optimal flow pressure for each well pattern unit. When the bottom hole flow pressure is lower than this value, even if the injection-production pressure difference further increases, there is small increase amplitude in production well productivity. This requires that a reasonable bottom hole flow pressure should be maintained during the actual reservoir water-flooding development process to avoid an excessive decrease in bottom hole flow pressure. If the bottom hole pressure is too low, it may also cause the fractures near the production well to close to a certain extent due to the pressure-sensitive effect, leading to decreased production. This method can provide an important theoretical basis for reservoir development of the same type.