储层矿物类型对致密油藏CO_(2)驱替效果的影响

Influence of reservoir mineral types on CO_(2)displacement effect of tight reservoir

为明确致密砂岩储层中石英、伊利石和绿泥石对CO_(2)驱油效率及孔隙动用特征的影响,分别选取以石英、伊利石、绿泥石为主要矿物类型的3种岩心,开展核磁共振扫描分析下的CO_(2)驱替实验,定量评价每种类型岩心在不同CO_(2)注入压力下小孔隙、大孔隙的原油采出程度,并分析了产出水中离子质量浓度变化。结果表明:目标储层以石英型和黏土矿物型为主,其中黏土矿物以伊利石和绿泥石为主;石英型岩心的CO_(2)驱替过程中,当CO_(2)注入压力小于等于最小混相压力时,大孔隙的原油动用程度大于小孔隙,当CO_(2)注入压力大于最小混相压力时,小孔隙的原油动用程度增加,而大孔隙的原油动用程度下降;伊利石型岩心大、小孔隙的原油采出程度最大,驱油效果最好,绿泥石型岩心大孔隙的原油采出程度很高,小孔隙的原油采出程度非常低,整体驱油效果最差;随着CO_(2)注入压力的增加,石英型岩心产出水中金属离子质量浓度大幅增加,伊利石型、绿泥石型岩心溶蚀后的钙、镁等离子产生沉淀,且绿泥石型岩心沉淀量最大,最易堵塞小孔隙。研究成果为致密砂岩油藏CO_(2)驱提供了参考和依据。

In order to clarify the impact of quartz,illite and chlorite in tight sandstone reservoir on CO_(2)displacement efficiency and pores producing characteristics,3 types of cores containing mainly quartz,illite and chlorite are used in CO_(2)displacement experiment with NMR scanning analysis to quantitatively evaluate recovery degree of oil in small and large pores of each type of core under different CO_(2)injection pressure and analyze mass concentration change of ions in produced water.The results show that the target reservoir is mainly quartz type and clay mineral type,and clay minerals are mainly illite and chlorite.In the process of CO_(2)displacement of quartz-type core,oil in large pores has higher producing degree of oil than that in small pores when CO_(2)injection pressure is lower than minimum miscible pressure and producing degree of oil in small pores increases when CO_(2)injection pressure is higher than minimum miscible pressure.Illite-type core has the highest recovery degree of oil in large and small pores and optimum displacement effect.Chlorite-type core has high recovery degree of oil in large pores and low recovery degree of oil in small pores,with the poorest overall displacement effect.With the increase of CO_(2)injection pressure,mass concentration of metal ions in produced water of quartz-type core increases greatly,dissolved calcium and magnesium ions in illite and chlorite type cores precipitate,and chlorite-type core has the largest precipitation amount and may block small pores.The research provides reference and basis for CO_(2)flooding in tight sandstone reservoir.