CO_(2)驱气体赋存特征微观可视化实验

Microscopic visualization experiment on gas occurrence characteristics in CO_(2)flooding

CO_(2)微观赋存特征对现场利用CO_(2)驱油提高采收率具有重要意义,然而目前的实验手段无法直观揭示CO_(2)驱油过程中的赋存状态,相关研究成果较少。采用微观渗流模拟技术,通过刻蚀不同孔喉特征二维微观可视模型,开展了CO_(2)混相与非混相驱及气驱后水驱微观可视化驱替实验,明确了不同驱替方式、不同驱替阶段和不同孔喉特征下CO_(2)的赋存特征。结果表明,CO_(2)赋存特征受驱替方式、驱替阶段和孔喉特征的共同影响,CO_(2)驱阶段,CO_(2)赋存特征主要受驱替方式影响,其次是孔喉特征影响;气驱过程中CO_(2)主要以连续相形式存在,但混相驱时局部CO_(2)富集且处于超临界状态,部分溶解在残余油中,而非混相驱富集现象不明显;气驱后转水驱过程中,CO_(2)赋存特征受驱替方式和孔喉特征的共同影响,混相驱替时,低渗透模型中气体赋存形式呈分散的泡状,细小喉道中存在段塞,高渗透模型中以密集的段塞为主、分散的泡状为辅;非混相驱替时,低渗透模型细小喉道中存在段塞,高渗透模型以小段塞为主,集中分布于喉道中间。研究成果有助于研究CO_(2)微观驱油机理和CO_(2)赋存特征,对提高CO_(2)驱油效率和辅助CO_(2)埋存研究具有理论指导意义。

The CO_(2)microscopic occurrence characteristics are significant for the study of CO_(2)flooding to enhance the oil recovery.However,the form variation and occurrence characteristics of gas in CO_(2)flooding have been rarely discussed so far.By using the microscopic flow simulation technology,a two-dimensional microscopic visualization model considering different pore throat characteristics was built.With the model,microscopic visualization displacement experiments were performed on CO_(2)miscible flooding,CO_(2)immiscible flooding,and water flooding after gas flooding,to clarify the occurrence characteristics of CO_(2)under different displacement processes,displacement stages and pore throat characteristics.The results show that the occurrence characteristics of CO_(2)are jointly controlled by displacement process,displacement stage and pore throat characteristics.During CO_(2)flooding,the occurrence characteristics of CO_(2)are mainly affected by displacement process,followed by pore throat characteristics.During gas flooding,CO_(2)occurs mainly as a continuous phase.During miscible flooding,CO_(2)is enriched and in a supercritical state locally,and partially dissolved in the residual oil.The phenomenon is unobvious during immiscible flooding.During water flooding after gas flooding,the occurrence characteristics of CO_(2)are jointly affected by displacement process and pore throat characteristics.During miscible flooding,the low-permeability model exhibits the gas occurrence in dispersive bubble form,and as slugs in fine throats,while the high-permeability model demonstrates the gas occurrence dominantly as dense slugs,supplemented by dispersive bubble form.During immiscible flooding,the low-permeability model shows slugs in fine throats,while the high-permeability model reveals the dominance of small slugs,which are concentrated between throats.The research findings are conducive to the study of CO_(2)microscopic displacement mechanism and occurrence characteristics,and of theoretical guiding significance for research on improvement of CO_(2)flooding efficiency and contribution to CO_(2)storage.