低渗油藏CO_(2)地质封存矿物颗粒运移及注入堵塞机理

Migration of mineral particles and mechanism of injection plugging during CO_(2) geological storage in low-permeability reservoirs

在低渗砂岩油藏中开展CO_(2)地质封存,是实现CO_(2)捕获、利用和封存(CCUS)的有效手段之一。随着CO_(2)持续注入吸收层,弱胶结砂岩颗粒会随CO_(2)流入孔隙和裂隙中运移,进而可能形成颗粒堆积,影响CO_(2)注入的稳定性。为揭示多形态颗粒在孔隙和裂隙中的运移、动态堆积及微观机理,建立了基于多形态矿物颗粒的离散元流固耦合堵塞模型。模型考虑了多级粒径、非规则形态、旋转、差异化流入孔隙模式等矿物颗粒参数及流体密度、流体速度等流体物性因素,模型可实现注入流体和矿物颗粒的瞬态堆积过程动态预测与可视化,并在此基础上揭示了CO_(2)物性、弱胶结非规则颗粒参数与注入堵塞间的量化关系。结果表明:(1)影响孔隙内矿物颗粒堆积数量和CO_(2)注入效果最高的因素为矿物颗粒质量分数,相对于颗粒质量分数3%,颗粒质量分数5%的孔隙内矿物颗粒堆积数量提升52.06%,孔隙内矿物颗粒堆积数量的提升比率与矿物颗粒质量分数增长比率呈负相关关系;(2)在注入CO_(2)和矿物颗粒总量一致情况下,当矿物颗粒平均尺寸为孔隙直径尺寸的1/3时,孔隙内矿物颗粒堆积数量最高,CO_(2)的注入效果最差,矿物颗粒密度变化对于CO_(2)注入的影响较低;(3) CO_(2)注入降低了砂岩孔隙内多相流体密度,减少了孔隙内矿物颗粒堆积数量,降低了矿物颗粒在孔隙内的堵塞,有利于CO_(2)往深部注入;(4) CO_(2)注入速度提升60%,孔隙内矿物颗粒堆积数量提升1.2%,注入速度提升增加了孔隙内的矿物颗粒堵塞比率,不利于CO_(2)的注入。

CO_(2) geological storage in low-permeability sandstone reservoirs is one of the effective means to realize CO_(2) capture,utilization and storage(CCUS).As CO_(2) continues to be injected into the absorbing layer,some weakly cemented sandstone particles will migrate with CO_(2) in pores and fractures.Particle accumulation is formed,which affects the stability of CO_(2) injection.In order to reveal the dynamic accumulation and microscopic mechanism of polymorphic sandstone particles,a discrete element fluid-solid coupling injection plugging model based on polymorphic sand particles was established.The model considers mineral particle parameters,such as multi-level particle size,irregular shape,and rotation,and fluid physical properties,such as fluid density and fluid velocity.The model can realize the dynamic prediction of the transient accumulation process of injected fluid and mineral particles.The quantitative relationship among CO_(2) physical properties,weakly cemented irregular sand parameters and injection plugging efficiency was revealed.The results indicate that:(1) the highest factor affecting the accumulation of mineral particles is the concentration of mineral particles.The particle concentration of 5% increases the accumulation of mineral particles in pores by 52.06% compared with the particle concentration of 3%.There is a negative correlation between the increase rate of particle accumulation and the increase rate of mineral particle concentration;(2) In the case of the same amount of injected CO_(2) and mineral particles,the accumulation is the highest when the average size of particles is 1/3 of the pore diameter.Small changes in mineral grain density have less impact on the CO_(2) injection.(3) The CO_(2) injection reduces the density of multiphase fluid in the sandstone pores,reduces the blockage of irregular mineral particles in the pores.(4) The CO_(2) injection rate increases by 60%,and the accumulation of mineral particles in the pores increases by 1.2%.The increase of injection velocity increases the plugging ratio of mineral particles in the pores,which is not conducive to the injection of CO_(2).