CO₂混相驱注气速率对重力超覆的影响规律

Effect of Gas Injection Rate on Gravity Segregation in CO₂ Miscible Flooding

赵凤兰 刘淼淼 黄世军 宋黎光 王 雨

ZHAO Fenglan LIU Miaomiao HUANG Shijun SONG Liguang WANG Yu

CO2驱可以改善低渗透油藏的开发效果，并通过置换油气等方式实现CO2地质埋存，但由于油气密度差的 存在，会形成CO2重力超覆而影响驱油效果。为明确油层厚度较大的低渗油藏中CO2混相驱条件下注气速率对 重力超覆程度的影响规律，分别采用室内物理模拟实验和数值模拟等方法进行研究，并通过建立的数值模型和 超覆程度表征方法，系统评价注气速率的影响规律，从而对注入量等参数进行优化。结果表明，混相驱条件下仍 存在一定程度的重力分异，且随注气速率的增加，重力超覆程度减弱，混相驱采收率提高，但相比非混相条件，超 覆程度较低，通过注气速率优化减弱其影响的效果更为明显。针对给定模型的模拟计算结果表明，当注入量大 于10 t/d后超覆程度影响减弱，因此，为保证厚油层CO2混相驱油效果，在不发生气窜的前提下应适当采用较大 的注气速率以减弱重力超覆的影响。研究结果对于CO2驱油现场试验方案设计和注气参数优化具有一定的指 导意义。

CO2 flooding can improve the development effect of low-permeability reservoirs，and realize CO2 geological storage by replacing oil and gas. However，due to the existence of oil and gas density difference，the CO2 gravity segregation affects the oil displacement effect. In order to clarify the effect of gas injection rate on the degree of gravity overlay under the condition of CO2 miscible flooding in low-permeability and thick oil reservoirs，laboratory physical simulation experiments and numerical simulation methods were used respectively. The research was carried out，and parameters such as injection rate were optimized through the established numerical model and the characterization method of the degree of segregation. The results showed that under miscible flooding conditions，there was still a certain degree of gravity differentiation，and with the increase of gas injection rate，the degree of gravity segregation decreased，and the recovery rate of miscible flooding increased. Compared with immiscible conditions，the degree of segregation was lower，the effect of reducing its influence by optimizing the gas injection rate was more obvious. The simulation calculation results for the given model showed that the influence of the overburden degree was weakened when the injection rate was greater than 10 t/d. Therefore，in order to ensure the CO2 miscible oil displacement effect in thick oil layers，a relatively large injection rate should be appropriately adopted to reduce the influence of gravity segregation without gas channeling. The research results have certain guiding significance for the design of the CO2 flooding field test scheme and the optimization of gas injection parameters.

10.19346/j.cnki.1000-4092.2023.02.021