非均质多层储层中CO2驱替方式对驱油效果及储层伤害的影响

低渗透油藏注CO₂开发过程中沥青质沉淀和CO₂-地层水-岩石相互作用引起的储层堵塞加剧了非均质多层砂岩储层中驱替特征的复杂性,影响CO₂和CO₂-水交替驱（CO₂-WAG）驱油过程中流体在储层中的渗流和最终的原油采收率。研究中的CO₂和CO₂-WAG驱油实验是在混相条件下（70℃、18 MPa）模拟的具有相似物性的多层储层系统中进行的,从油气产量、剩余油分布和渗透率损害3方面评价了两种驱替方式。实验结果表明,CO₂驱后整个系统的采收率较低,产油主要来自高渗透层,剩余油分布在中、低渗透层。CO₂-WAG驱过程中CO₂突破时间较晚,整个系统的原油采收率显著改善。此外,CO₂驱后高渗透层的渗透率下降了16.1%,95.1%的下降幅度是由沥青质沉淀引起。在CO₂-WAG驱后,各层的渗透率下降幅度分别为29.4%、16.8%和6.9%,沥青质沉淀仍是主要因素,且引起的储层堵塞更严重,但高渗透层中CO₂-地层水-岩石相互作用引起的渗透率下降不容忽视,占20.7%的因素。因此,对于具有强非均质性的多层储层,CO₂-WAG具有更好的驱油效果,但是对沥青质沉淀的预防和控制措施是必要的。

Influence of CO2 flooding mode on oil displacement effect and reservoir damage in heterogeneous multi-layer reservoirs

During the development of low-permeability reservoirs by CO₂ injection, reservoir blockage caused by asphaltene precipitation and CO₂-formation water-rock interaction exacerbates the complexity of displacement characteristics in heterogeneous multilayer sandstone reservoirs, thus affecting the seepage of fluids in reservoirs and final oil recovery during CO₂ and CO₂-WAG flooding. In this study, the CO₂ and CO₂-WAG flooding experiments were conducted in simulated multi-layer reservoir systems with similar physical properties under miscible conditions (70℃, 18 MPa). The two displacement modes were evaluated in terms of oil and gas production, remaining oil distribution and permeability damage. The experimental results show that the oil recovery of the entire system is lower after CO₂ flooding, the oil production is mainly from the high permeability layer, the remaining oil is distributed in the medium and low-permeability layers. During the CO₂-WAG flooding, the CO₂ breakthrough time was late, and the oil recovery of the entire system was significantly improved. In addition, the permeability of the high-permeability layer decreased by 16.1% after CO₂ flooding, and 95.1% of the decrease was caused by asphaltene precipitation. However, after CO₂-WAG flooding, the permeability of each layer decreased by 29.4%, 16.8%, and 6.9%, respectively. Asphaltene precipitation is still the main factor and causes even more serious reservoir blockage. Moreover, the permeability decline caused by CO₂-formation water-rock interaction in the high-permeability layer cannot be ignored, contributing 20.7% of the corresponding factors. Therefore, for multi-layer reservoirs with strong heterogeneity, CO₂-WAG flooding has better oil displacement effect, but the prevention and control measures for asphaltene precipitation are necessary.