CO2-Assisted Heavy Oil Displacement and Drainage Composite Process: Physical Simulation and Field Application

In view of the problems of unbalanced scale development of composite steam chamber, a lack of production capacity advantage of well group and low oil–gas ratio in heavy oil, physical simulation experiments with an acrylic-plate visual model, foamy-oil stability tests, coreflood, and a three-dimensional physical model were conducted to investigate the displacement behavior and auxiliary effects of CO2, and the multiple driving effects of CO2 in auxiliary steam drive were analyzed. The experimental results show that CO2-assisted steam drive has multiple driving mechanisms, such as favoring steam turning to expand the swept volume, starting residual oil at edge of narrow pores, and emulsifying foam oil flow, and the steam swept range reaches 79.6%, 38.3 percentage points higher. Partial CO2 gas occupies the reservoir space to promote the steam chamber to expand to the horizontal section of the production well in a “face-body”, forming a composite production mode of steam chamber superimposed drive and latent heat gravity oil displacement, and the crude oil is produced in a stable foam oil flow, and the final recovery is on the order of 70%, with a comprehensive oil–steam ratio of 0.189, and CO2 oil exchange rate 0.21 mL/Ncm3. The results of the mine field test show that the well group productivity and oil–gas ratio of CO2-assisted drive and drainage composite are significantly improved, and there is broad application prospect for CO2 utilization and enhanced heavy-oil recovery in displacement-and-drainage composite development.