Improving heavy oil recovery using a top-driving, CO2-assisted hot-water flooding method in deep and pressure-depleted reservoirs

The primary recovery of conventional heavy oil (with viscosity < 150 mPa s) in deep reservoirs often has a low recovery factor (RF) and high-pressure drawdown. It is important to propose effective and economic recovery methods to enhance oil recovery of these reservoirs. A top-driving, carbon dioxide (CO2)-assisted hot-water flooding method is developed and presented in this paper. Laboratory experiments, including CO2 solubility and one-dimensional (1D) core flooding tests, were conducted based on oil samples from a deep and pressure-depleted conventional heavy oil reservoir. Numerical simulations were conducted to study and discuss the mechanisms. The results from laboratory experiments show that the dissolved CO2 in the oil reduced the oil viscosity by 30% at 57 degrees C and 2.0 MPa, and the displacement efficiency of carbonated 120 degrees C hot-water flooding was comparable to that of 200 degrees C steam flooding. The CO2-assisted hot-water flooding method requires substantially less energy input than the steam flooding method. Numerical simulation indicates that the CO2 and hot-water co-injecting process results in viscosity reduction, increased pressure, increased sweeping volume, and, consequently, improved oil recovery. The top-driving and CO2-assisted hot-water flooding method provides a technical and cost-effective method for enhancing oil recovery in the post-primary recovered heavy oil reservoirs.