二氧化碳驱后微粒运移对低渗透储层的伤害及对渗流能力的影响

Damage of Particle Migration after CO₂ Flooding to Low Permeability Reservoir and Its Influence on Seepage Capacity

刘漪雯 付美龙 王长权 许诗婧 孟凡坤 沈彦来

LIU Yiwen FU Meilong WANG Changquan XU Shijing MENG Fankun SHEN Yanlai

CO2驱是高含水油藏三次采油有效的技术措施。利用现有井网转注CO2是目前低油价下经济可行的开发 方式。虽然在驱替过程中引起的微粒运移会对岩石孔喉造成堵塞，但注入CO2能有效降低注入压力，且在注入 过程中发生的溶蚀作用整体上提高了流体的渗流能力。通过开展CO2驱后微粒运移堵塞规律实验及CO2-水溶 液对岩石溶蚀评价实验，并对驱替前后的相渗曲线变化特征进行评价，进一步说明CO2驱对储层渗流能力的影 响。结果表明，在注入CO2的过程中，注入速度为0.1、1.0 mL/min时的注入压力均有所降低。有油条件下CO2驱 后的岩心渗透率损失为37.05%，而经甲苯和无水乙醇清洗岩心后，岩心渗透率恢复30.48%，说明微粒在运移过 程中会被原油束缚，积聚成团，造成堵塞。虽然存在一定的堵塞，但CO2-水溶液主要与绿泥石发生反应，并释放 Ca2+、Mg2+、Fe2+等离子，其中Ca2+浓度增长137.05%、Mg2+浓度下降52.20%、Fe2+浓度下降49.45%，说明虽然产生的MgCO3、Fe2O3等会对岩石孔喉造成堵塞，但CO2对CaCO3的溶蚀作用更强，整体上提高了流体的渗流能力，从而 在一定程度上改善了后续水驱的注水能力及效果。CO2驱前后，相渗曲线中束缚水饱和度增加，残余油饱和度降 低，两相共渗区增大，驱油效率增加，进一步说明CO2驱产生的溶蚀作用整体上增大了孔隙空间和渗流通道，提 高了注入水的注入能力。

CO2 flooding is an effective technical measure for tertiary oil recovery in high water cut reservoirs. Using the existing well pattern to inject CO2 is an economical and feasible development method under low oil price. Although the particle migration caused by the displacement process will block the pore throat of rock，the injection of CO2 can effectively reduce the injection pressure，and the dissolution occurred during the injection process improves the seepage capacity of fluid as a whole. By carrying out the experiment of particle migration plugging law after CO2 flooding and the evaluation experiment of CO2-aqueous solution on rock dissolution，and evaluating the variation characteristics of relative permeability curves before and after displacement，the influence of CO2 flooding on reservoir seepage capacity was further explained. The results showed that during the injection of CO2， the injection pressure decreased when the injection rate was 0.1 mL/min and 1.0 mL/min. The core permeability loss was 37.05% after CO2 flooding under the condition of oil，while the core permeability recovery was 30.48% after cleaning the core with toluene and anhydrous ethanol，indicating that the particles would be bound by crude oil during the migration process，accumulate into clusters，and cause blockage. Although there was a certain blockage，the CO2-aqueous solution mainly reacted with chlorite and released Ca2+，Mg2+，Fe2+ and other ions. The concentration of Ca2+ increased by 137.05%，the concentration of Mg2+ decreased by 52.20%，and then the concentration of Fe2+ decreased by 49.45%. It showed that although the generated MgCO3 and Fe2O3 would block the pore throat of rock，the dissolution of CaCO3 by CO2 was stronger，which improved the seepage capacity of the fluid as a whole，thus improving the water injection capacity and the effect of subsequent water flooding to a certain extent. The irreducible water saturation in the relative permeability curve before and after CO2 flooding increased，the residual oil saturation decreased，the two-phase seepage area increased，and then the oil displacement efficiency increased. It further indicated that the dissolution produced by CO2 flooding increased the pore space and seepage channel as a whole，and then improved the injection capacity of injected water.

10.19346/j.cnki.1000-4092.2024.02.007