Coupled Lab-Scale and Numerical Analysis for Fault Critical Re-Active Stress Evaluation

Dual-horizontal-well SAGD, proven effective in Canada's oil sands and China's Fengcheng extra-heavy oil reservoir, faces challenges in shallow, high-viscosity reservoirs with strong heterogeneity—including thin muddy laminae and interbedded mudstones—resulting in prolonged preheating and uneven steam chamber development. This study integrates lab-derived rock mechanics data to establish a coupled stress field model, analyzing dilation characteristics during SAGD startup via geomechanical simulation. For shallow uncemented faults (common in high-porosity, unconsolidated formations), conventional fault-seal assessment methods (SGR/displacement pressure) prove inadequate. Applying Byerlee's slip criterion, we calculate critical fault instability pressures (2.74–4.26 MPa), recommending a reduced friction coefficient (0.4–0.5 versus typical 0.6–1.0) for water-saturated, unconsolidated fill zones. Reservoir dilation significantly enhances interwell properties, accelerating steam injection and establishing hydraulic connectivity to shorten preheating.