Study On Calculation Method Of Production-injection Well Spacing In Ultra-low Permeability Reservoir

At present,China's low-permeability oil reservoirs,especially ultra-low permeability reservoirs,have relatively low levels of utilization and poor development results.They still have great potential for development.However,the reasonableness of injection and production well spacing affects low permeability and ultra-low permeability reservoirs.The key factors for the development of the effect,therefore,the study of a reasonable injection well spacing calculation method is of great significance for the effective development of low permeability reservoirs.Firstly,according to the reservoir characteristics of low-permeability and ultra-low permeability reservoirs,the pressure-sensitive effect and starting pressure gradient are introduced into the formation pressure distribution calculation model,and the method for determining the drainage radius is given.Secondly,under consideration of single-phase flow conditions only,a pressure distribution calculation model was established for injection wells and production wells respectively,and a pressure distribution calculation method and pressure distribution calculation method for production well areas were deduced,and a limit injection well was also given.Method of determination.In the case of oil-water two-phase flow,the injection well area is considered as the oil-water two-phase flow area and the single-phase oil flow seepage area.The oil well area is considered as a single-phase oil flow,and the ratio of the two-phase fluidity to the single-phase fluidity is defined.Based on the flow characteristics of different phase-permeability curves,based on the two-phase flow theory,the pressure distribution methods for water injection wells and production wells are deduced,and the calculation method for injection well spacing is given.Finally,based on the oil-water two-dimensional two-phase numerical simulation theory,the effects of starting pressure gradient and pressure-sensitive effect are introduced simultaneously,the mathematical model is improved,the difference equation and the computer model are established,and the two-phase flow conditions are achieved.Numerical solution.The study shows that when the single-phase oil flow is considered in the injection well area,the limit injection radius is larger than the drainage radius;the larger the starting pressure gradient,the smaller the limit injection radius and the drainage radius;under the two-phase flow conditions,the change of the phase permeability curve Well spacing has a significant influence.When the ratio of the average value of flow degree at the front edge of the waterflood to the maximum water saturation to the single-phase oil flow is less than 1,the injection-production well spacing under the two-phase seepage is less than that under single-phase oil flow.When the injection well spacing and average fluidity ratio are greater than 1,the injection-production well spacing is larger than that of single-phase flow.The numerical method results show that the larger the variability,the larger the injection well spacing and the larger start-up pressure gradient.The smaller the distance,the larger the ratio between the average value of the two-phase flow degree and the single-phase fluidity corresponding to the percolation curve,the greater the injection-production well spacing.