低渗油藏水驱后CO_2潜力评价及注采方式优选

CO_2 flooding potential evaluation and its injection-production method optimization after water flooding in low permeability reservoir

针对延长油田乔家洼区块由于基质致密和非均质性严重造成注水开发效果差的问题,通过开展CO2室内驱油实验,在水驱基础上分别对连续气驱和气水交替驱驱油潜力进行评价,并对气水交替驱流体注入速度、段塞尺寸及气水比等注入参数进行优化。同时,对区块采用水驱、优化井网后水驱、利用优化的CO2驱注入参数开展气驱和注气5年后转气水交替驱4种开发方案,进行数值模拟产量预测。实验结果表明,CO2驱在目标区块高含水后有着较大驱油潜力,连续气驱和气水交替驱分别在水驱基础上可提高采收率8.43%和20.95%;气水交替注入方式下采收率随各注入参数的增大均呈先增加后降低的趋势,最佳注入速度、最佳注入段塞尺寸和最佳气水比分别为0.73mL/min、0.1PV和1∶1。数值模拟结果表明:优化井网后水驱、连续气驱和注气5年后转气水交替驱3种方案在开发15年后,分别可以在原水驱方案基础上提高采收率0.77%、13.81%和12.98%,建议采用注气5年后转气水交替驱方案进行生产。

Due to dense matrix and serious heterogeneity,the water flooding development effect is poor in Qiaojiaowa block,Yanchang Oilfield.Therefore,CO2 indoor flooding experiment is carried out to potentially evaluate CO2 flooding and water alternating gas（WAG）on the basis of water flooding,and optimize the injection parameters such as injecting velocity,slug size and the ratio of gas and water.Besides,yield predictions of water flooding,water flooding based on well optimized,CO2 flooding and WAG after injection CO2 for 5years are conducted using numerical simulation.Experimental results show that it is a large potential in target block for CO2 flooding after water flooding.The enhanced oil recovery（EOR）improvement of CO2 flooding and WAG are 8.43%and 20.95%respectively compared with water flooding.Oil recovery with WAG increases first and then decreases with three injection parameters increase.The best injected velocity,slug size and gas-water ratio are0.73mL/min,0.1PV and 1∶1.Simulation results show that the EOR improvement of water flooding based on well optimized,CO2 flooding and WAG after injecting CO2 for five years after developing15 years are 0.77%,13.81% and 12.98%respectively compared with water flooding.The suggested production plan is WAG after injecting CO2 for five years.