The SAGD start-up process normally circulates steam in both the injector and producer, which consumes a large amount of steam, requires the high cost of high-temperature-produced liquid treatment, and unavoidably results in preferential communication in heterogeneous reservoirs. In order to achieve uniform preheat and full steam chamber development in SAGD wellpairs, downhole electrical heating to start up SAGD was proposed and investigated in this study using physical and numerical simulation approaches. Two 3-D scaled physical experiments were designed and implemented to investigate the feasibility and heating characteristics of such a method. Numerical simulation was conducted using an SAGD sector model with typical field properties to design the preheating process, optimize key operational parameters, and formulate the soak strategy to determine the SAGD conversion timing. The experimental results indicate that electrical heating outperforms steam circulation in achieving the uniform thermal communication in heterogeneous reservoirs, which is challenged in the conventional steam circulation process. The preheating process and operational parameters of electrical heating were formulated and optimized, which include wellbore pre-flush, wellbore saturation by heat conduction fluid, electrical heating, and replacement of heat conduction fluid periodically. Surveillance of temperature difference along the horizontal section while powering off electrical heating intermittently is optimized to be the SAGD conversion timing determination strategy. Based on the combination results of scaled physical simulation and pilot wellpair numerical simulation, full heat communication and steam chamber development are achieved along the horizontal length by electrical preheating, and the oil recovery factor of the pilot wellpair is enhanced by 14.8%, indicating encouraging potentials in heavy oil and bitumen development.

In the process of steam injection development of heavy oil, due to the serious heterogeneity and interference of steam channeling in the high-permeability layer, there is a lot of oily sludge in the produced liquid of oil wells, which is difficult to deal with. According to existing profile control technology and the related properties of oily sludge, a profile control system was developed by using oily sludge as the main agent and by adding other additives. At the same time, the properties of sludge, the matching relationship between the particle size of sludge and the formation of pore roar, the temperature resistance, the plugging ability, and other contents were studied. The agent featured an adjustable curing time (3 to 300 h) and resistance to pressures greater than 6 MPa and temperatures greater than 350 °C. After the agent was injected into the high-permeability steam channeling, the system was cemented with the formation rock and the sealing rate was more than 85%, without any damage to the low- and medium-permeability layers. According to the different characteristics of the production well and steam injection well, the construction technology was optimized, the oily sludge profile control technology suitable for heavy oil reservoirs was formed, and the field test was carried out. At present, more than 150 wells have been used in the field, with a cumulative oil increase of 10,756 tons. The technology not only solves the environmental pollution caused by oily sludge but also reduces the cost of thermal recovery of heavy oil, with great significance for improving the final recovery efficiency and commercial benefits of the oilfield.

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.