An innovative in situ solvent generation enhanced SAGD technique: Mechanism analysis based on numerical simulation.

• An in situ bitumen decomposition kinetic model is developed. • The significance of bitumen decomposition to oil recovery is discussed. • A green and economical recovery tech without steam additives injection from surface. • The tech has higher oil production, lower steam consumption and carbon emission. In the late stages of Steam Assisted Gravity Drainage (SAGD) development, the increase in steam chamber volume and greater heat losses result in elevated thermal losses, and increased CO 2 emissions, leading to reduced economic efficiency. To address this issue, this paper proposes a pioneering approach, termed the in situ solvent generation enhanced SAGD technique (ISSG-SAGD). Through a comprehensive review of Athabasca bitumen aquathermolysis, thermal cracking, and their phase behavior with solvents, a general reaction kinetic model and fluid model are established. Subsequently, the feasibility and recovery mechanism of ISSG-SAGD are elucidated by employing numerical simulation that compares SAGD with ISSG-SAGD. Results show that, in comparison to SAGD, ISSG-SAGD reduces steam consumption by 13.77 %, lowers carbon intensity by 18.12 % and increases oil production by 5.48 %. These advantages arise from the synergistic integration of recovery mechanisms characteristic of Expanding Solvent SAGD (ES-SAGD) and Steam and Gas Push (SAGP). Notably, non-condensable gas accumulation above the steam chamber diminishes heat loss while replenishing reservoir energy. Simultaneously, light hydrocarbons are strategically positioned at the drainage interface, leading to a reduction in residual oil saturation and an increment in drainage rates. Consequently, ISSG-SAGD emerges as an environmentally sustainable and economically viable trajectory for heavy oil development. [ABSTRACT FROM AUTHOR]