Effective injection-production well spacing in pressure-sensitive reservoir with low permeability

For designing effective injection and production well spacing in low permeability reservoirs, it's essential to consider the pressure-sensitive effects arising from various pressure changes during the operation of injection and production wells, along with the impact of changes in the start-up pressure gradient. This study builds upon the basic seepage laws of low-permeability reservoirs to establish a seepage equation that incorporates the effects of the starting pressure gradient and pressure sensitivity. Utilizing the stable successive substitution method, the study examines the pressure distribution and the mechanism of reserve production under typical injection-production patterns. Based on the different requirements of the daily output of oil wells in an actual oil fields, a method for solving the effective injection-production well spacing of low-permeability pressure sensitive reservoir is determined. The study shows that, using the pressure sensitivity of the injection and production well area as a benchmark, there is a notable difference in the calculated results for well spacing when compared with scenarios where pressure sensitivity is either not considered or only considered for the production well area. Specifically, these differences are +9.8 % and -20.6 % under the same conditions. Considering the production limit requirements, the effective injection-production well spacing is about 0.7 ~ 0.9 times of the limit injection-production well spacing under normal conditions, which can better guide the reasonable deployment of the development well pattern of low permeability pressure sensitive reservoirs.