CO_2驱水气交替注采参数优化——以安塞油田王窑区块长6油藏为例

Optimization design of injection and production parameters for water-alternating-CO_2 flooding: a case study of Chang 6 reservoir of Wangyao block in Ansai oilfield

针对安塞油田王窑区块长6特低渗透油藏现阶段注水开发矛盾突出的问题,为进一步提高油藏采收率,评价CO2驱油效果,应用油藏数值模拟方法,优化了CO2驱水气交替注采参数。利用Eclipse的PVTi模块模拟了注气膨胀实验,研究了注CO2对原油相态的影响;采用正交试验设计方法,以提高采出程度和换油率为目标,对CO2驱水气交替过程中的气水比、注气速度、关井气油比和段塞注气量4个参数进行了优化研究,并用直观分析方法对试验结果进行分析。结果表明,当原油中溶解的CO2物质的量分数达到60%时,原油粘度降低幅度达80.51%,原油体积膨胀1.44倍;优化得到的最优气水比为1∶1,注气速度为13 000 m3/d,关井气油比为1000 m3/m3,段塞注气量为0.005倍孔隙体积。

The Chang 6 reservoir of Wangyao block in Ansai oilfield belongs to extra-low permeability formation, and prominent prob-lems exist during the current water flooding. In order to enhance the oil recovery and evaluate the effect of CO2 flooding, optimizationdesign of injection and production parameters for water alternating gas flooding is conducted with reservoir numerical simulation meth-od. The PVTi module of Eclipse is used to simulate the gas-injection expansion experiment to analyze the effect of injected CO2 on thephase behavior of crude oil. With the orthogonal experiment design, four injection and production parameters are studied, includinggas-oil ratio, CO2 injection rate, shut-in gas oil ratio and CO2 slug size. Visual analysis method is applied to analyze the test result. Theresults show that when the mole fraction of the dissolved CO2 reaches 60%, the viscosity of the oil reduces by 80.51% and the coeffi-cient of volumetric expansion reaches 1.44. The optimal combination of parameters is that the gas-oil ratio is 1∶1, gas injection rate at13 000 m3/d, shut-in gasoilratio at 1 000 m3/m3and CO2 slug size at 0.005 pore volume.