Infill wells assisted in-situ combustion following SAGD process in extra-heavy oil reservoirs

The steam oil ratio (SOR) usually increases during the later steam-assisted gravity drainage (SAGD) process, resulting in a decrease in economic benefits and an increase of oil remaining in the wedge zones. To extract wedge zone oil efficiently and economically, this study proposed a method, namely infill wells assisted in-situ combustion (ISC) following SAGD, which takes advantages of SAGD and ISC in sequence by proper well patterns. The requirements for successful ISC following SAGD were discussed, including fuel supply, thermal communication, high temperature oxidation (HTO) kinetics, and the proper time to convert to ISC and the proper well patterns for ISC. The potential method was studied systematically by both physical and numerical simulations based on parameters of a typical extra-heavy oil reservoir in China. The results show that SAGD can be converted to ISC when the steam chamber extends to the edge of SAGD well pattern with infill wells in the middle of well pair as air injectors. It is shown that infill wells assisted ISC following SAGD method has great potential for enhancing oil recovery in extra-heavy oil reservoirs and also presents good economic benefit and operability due to its high oil efficiency. With the well pattern recommended, the oil recovery and economic benefit can be improved by 12.8% and 26.4%, respectively, compared to continued SAGD process. This will provide important guidance for the development in extra-heavy oil reservoirs worldwide.