长岩心CO2非混相驱中注气速率对重力超覆的影响

Effect of Gas Injection Rate on Gravity Segregation during CO2 Long Cores Immiscible Flooding

赵凤兰 宋黎光 冯海如 王 强

ZHAO Fenglan SONG Liguang FENG Hairu WANG Qiang

针对室内难以模拟真实油气运移中重力超覆的问题，课题组自主研制了一种二维高温高压气驱超覆物理 模型，通过上下层产出流体差异对超覆程度进行表征，开展不同注气速率下长岩心CO2非混相驱实验，利用岩心 上、下层气体突破时采收率比值、最终采收率及岩心剖面剩余油分布等评价重力超覆程度，并分析注气速率对重力 超覆的影响机理。研究结果表明，以0.1 mL/min的低注入速率注入时，岩心下层几乎不产油，上层采收率所占比重 高达97.5%，岩心整体波及效率低，最终采收率仅为49.49%，重力超覆严重；注气速率逐渐增加至1 mL/min，岩心上 层采收率所占比重由97.5%逐渐降至50.9%，最终采收率高达60.26%，岩心剖面剩余油随注气速率增加而减少，重 力超覆减弱。随注气速率的增加，CO2水平黏性力增大，对油气密度差引起的垂向重力抑制作用增强，重力超覆减 弱，岩心整体波及效率得到改善。实验结果可为低渗油藏CO2驱注气参数优化提供理论依据。

Aimed at the problem that it is difficult to simulate the gravity segregation in real reservoir condition by indoor experiments，the gravity segregation physical model in high temperature and high- pressure gas flooding that can stimulated the gravity segregation under reservoir conditions was developed independently. the gravity segregation physical model in high temperature and high pressure gas flooding that can stimulated the gravity segregation under reservoir conditions was developed and gravity segregation was characterized by the produced fluid difference of upper and lower layers，CO2 immiscible flooding using long cores was conducted to study gravity segregation at different injection rates，the gravity segregation degree was evaluated through oil recovery proportion at upper and lower layers of core when gas breakthrough，final recovery and core displacement profiles，and the mechanism that how gas injection rate affected gravity segregation was also analyzed. The results showed that，the gravity segregation was serious that oil recovery of lower layer was nearly zero and oil recovery of top reached up to 97.5% when gas injection rate was at low value of 0.1 mL/min，resulting in the whole sweep efficiency of core was so poor that final oil recovery was only 49.49%. The oil recovery proportion of upper layer reduced to 50.9% as gas injection rate increased from 0.1 mL/min to 1 mL/min，and the final oil recovery even reached up to 60.26%. The residual oil of core displacement profiles decreased since gas injection rate increased，indicated that the gravity segregation degree got weaken. With increasing gas injection rate，CO2 level viscous force increased，the suppression of vertical gravity caused by oil- gas density difference was enhanced，the core sweep efficiency was improved as gravity segregation declined. Experimental results can provide theoretical basis for optimization of CO2 flooding gas injection parameters in low permeability reservoirs.

10.19346/j.cnki.1000-4092.2021.02.015