Dimethyl ether-assisted steam-assisted gravity drainage: Effects of injection timing on steam chamber evolution and recovery dynamics

Dimethyl ether (DME)-assisted steam-assisted gravity drainage (SAGD) offers transformative potential for heavy oil recovery by enhancing steam chamber evolution while reducing energy consumption and environmental impact. Through two-dimensional physical modeling, this study systematically evaluates the effects of DME injection timing—early, middle, and late stages—on steam chamber evolution, recovery dynamics, and energy efficiency. Results identify middle-stage injection as the optimal strategy, achieving a 65% oil recovery factor and a cumulative oil–steam ratio of 0.17, surpassing early-stage (58%), late-stage (55%), and traditional SAGD (53%). Mechanistically, DME accelerates steam chamber growth by enhancing thermal connectivity and reducing heavy oil viscosity. Middle-stage injection aligns DME presence with the critical lateral expansion phase, forming a broader, more symmetric chamber with enhanced sweep efficiency and reduced residual oil saturation. Early-stage injection accelerates vertical growth but suffers from rapid solvent depletion, limiting its long-term impact. Late-stage injection targets unswept zones in the exhaustion phase but lacks sufficient operational duration for significant improvement. Steam chamber analysis reveals DME's dual role: improving heat transfer pathways and expanding oil mobility zones. Production dynamics confirm sustained benefits in middle-stage injection, which maintains higher oil production rates and energy efficiency. Residual oil distribution further highlights the superiority of this approach, achieving the most uniform displacement and minimal unswept regions. This study underscores the pivotal role of injection timing in optimizing DME–SAGD performance, providing a scalable solution to enhance oil recovery while minimizing environmental and economic costs.