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 CO_(2) Flooding to Low Permeability Reservoir and Its Influence on Seepage Capacity

CO_(2)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CO_(2)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CO_(2)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CO_(2)驱后微粒运移堵塞规律实验及CO_(2)-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CO_(2)驱对储层渗流能力的影响。结果表明,在注入CO_(2)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CO_(2)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CO_(2)-水溶液主要与绿泥石发生反应,并释放Ca^(2+)、Mg^(2+)、Fe^(2+)等离子,其中Ca^(2+)浓度增长137.05%、Mg^(2+)浓度下降52.20%、Fe^(2+)浓度下降49.45%,说明虽然产生的MgCO_(3)、Fe_(2)O_(3)等会对岩石孔喉造成堵塞,但CO_(2)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。CO_(2)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CO_(2)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。

CO_(2) flooding is an effective technical measure for tertiary oil recovery in high water cut reservoirs.Using the existing well pattern to inject CO_(2) 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 CO_(2) 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 CO_(2) flooding and the evaluation experiment of CO_(2)-aqueous solution on rock dissolution,and evaluating the variation characteristics of relative permeability curves before and after displacement,the influence of CO_(2) flooding on reservoir seepage capacity was further explained.The results showed that during the injection of CO_(2),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 CO_(2) 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 CO_(2)-aqueous solution mainly reacted with chlorite and released Ca^(2+),Mg^(2+),Fe^(2+)and other ions.The concentration of Ca^(2+)increased by 137.05%,the concentration of Mg^(2+)decreased by 52.20%,and then the concentration of Fe^(2+)decreased by 49.45%.It showed that although the generated MgCO_(3) and Fe_(2)O_(3) would block the pore throat of rock,the dissolution of CaCO_(3) by CO_(2) 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 CO_(2) 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 CO_(2) flooding increased the pore space and seepage channel as a whole,and then improved the injection capacity of injected water.