Decarbonizing SAGD in heterogeneous ultra-heavy-oil reservoirs: barrier-bypassing well patterns and geomechanical dilation cut steam demand and CO2 emissions

The shallow ultra-heavy oil reservoirs in Karamay, China are characterized by proximal braided-river continental settings, strong heterogeneity, well-developed interlayers, and multiple vertical flow barriers. The application of conventional dual-horizontal well SAGD (Steam-Assisted Gravity Drainage) technology in such reservoirs often results in slow steam chamber development and low oil drainage rates, limiting production performance and oil-steam ratio, and posing significant challenges for efficient reservoir development. To address these issues, this study conducted reservoir architecture analysis and detailed interlayer characterization to establish interlayer distribution patterns and better understand reservoir heterogeneity. Physical and numerical simulations were employed to investigate steam chamber growth and gravity drainage behavior under multiple flow barriers. Based on these insights, technical strategies for barrier breakthrough and flow improvement were developed. Several innovative well patterns and reservoir geomechanical dilation and stimulation techniques were proposed, including vertical-horizontal well combinations, dual-layer staggered configurations, and parallel-parallel linear arrangements. These approaches promote vertical steam chamber growth and enhance oil drainage rates, leading to the formation of an efficient three-dimensional drainage system. Field application in 109 SAGD well pairs demonstrated significant improvements, with oil production rates increased by 20%–40% and recovery factors enhanced by 10–15 percentage points, thereby lowering steam demand and associated CO2 emissions. Drawing on a decade of integrated research and field application, this executive review distils transferable lessons that can accelerate and de-risk SAGD development in similarly heterogeneous ultra-heavy-oil reservoirs worldwide.