低渗透油藏蓄能增渗压力规律数值模拟

Numerical Simulation of the Pressure Law of Energy Charging and Permeability Enhance⁃ment in Low Permeability Reservoirs

针对延长油田注水开发中存在的高压注不进、难见效、含水上升快等问题,创新性地提出了蓄能增渗注水技术。运用油藏数值模拟方法研究了蓄能增渗注入和焖井期间裂缝、基质压力演变及井底压力传播规律,同时分析了注入量对蓄能增渗效果的影响。研究发现,在注入阶段中,随着水的快速注入,裂缝内压力升高,注入水由主裂缝向裂缝尖端传递,压力升高区域主要分布在裂缝周围,基质压力变化不大。在焖井阶段中,随焖井时间延长,裂缝及近裂缝带基质压力表现为先迅速下降,超过一定焖井时间后趋于稳定;距离裂缝大于30 m的基质压力随焖井时间延长出现先上升后下降的趋势。井底压力同样表现为焖井初期迅速下降,后期趋势变缓。注入量越高,地层能量提升越高。进一步剖析了低渗透油藏蓄能增渗作用机理。矿场应用证明该技术提压增油效果显著,可为类似油藏蓄能增渗开发提供经验借鉴。

A number of problems have been experienced with water injection in Yanchang Oilfield,such as high-pressure injection failure,poor flooding effect,and rapid increase of water cut during injection.An innovative method for energy charging and permeabili-ty enhancement is proposed to address these issues.Numerical reservoir simulation is used to study the evolution of fractures,matrix pressure,and bottom hole pressure propagation during injection and well shut in.The influence of injection volume on fracturing effect is also analyzed.It is found that,during the injection stage,rapid injection of fluid increases the pressure in the fracture,with the inject-ed fluid passing through the main fracture to the tips of the fractures.The pressure increase mainly occurs around the fracture itself,with little change in the matrix pressure.In shut in stage,as shut in time increases,the matrix pressure in the fracture and near-fracture zone initially decreases rapidly and then tends to become stable after a certain time.If the distance from the fracture is more than 30 m,the matrix pressure first increases and then decreases with the increase of shut in time.The bottom hole pressure also declines rapidly in the early stage of shut in with the rate of decline slowing in the later stage.The greater the injection volume,the higher the formation energy.Analysis of the effect of energy charging and permeability enhancement in field applications for low permeability reservoirs shows remarkable increases in pressure and oil production.This provides a valuable reference for the development of energy charging and permeability enhancement in similar reservoirs.