致密油藏润湿返转提高采收率技术

Enhanced Oil Recovery by Wettability Alteration Method for Tight Reservoirs

针对致密油藏目前开采方式存在产量递减快、可采储量低的问题,通过构建基于离散裂缝网络的致密油藏润湿返转提高采收率数学模型,并编制相应全隐式数值求解算法,进一步研究了亲油储层周期注入表面活性剂方式的驱油效果及影响因素。结果表明:周期注入表面活性剂能够使储层产生润湿性返转,诱导自发渗吸,进而有效动用基质内剩余油,较目前开采方式可进一步提高采收率幅度10%;周期注表活剂的驱油效果随着原油黏度的降低、基质渗透率的增大或者压裂密度的提高而变好,当地层原油黏度低于7mPa·s、基质渗透率不低于0.01mD、裂缝间距不高于150m时,周期注表活剂可取得明显的增油效果。

Low primary recovery factors and rapid production decline in tight oil reservoirs,imply a promising opportunity for developing effective enhanced oil recovery(EOR)methods to mobilize the residual oil resource,especially for oil-wet reservoirs.A discrete-fracture-network-based mathematical model for EOR with wettability alteration in tight oil reservoirs is proposed and numerically solved by the fully implicit method.Simulation cases are conducted to investigate the production performance and key impact factors of cyclic surfactant injection.Cyclic surfactant injection can significantly improve production performance of oil-wet tight reservoirs,the reason is that surfactant can alter reservoir wettability from oil wet to medium or even water wet,which trigger spontaneous imbibition and favor oil movement from matrix into fracture.Its EOR results get better with oil viscosity decreasing,matrix permeability increasing or fracture spacing decreasing.Cyclic surfactant injection is good when the oil viscosity is less than 7 mPa·s,matrix permeability is bigger than 0.01 mD and fracture spacing is less than 150 m.