Impact of fault slip induced by water injection on casing deformation: a numerical study

Abstract

Fluid injection can cause fault reactivation and slip due to weakened cementation strength. The resulting fault slippage poses significant challenges to wellbore and casing integrity. To address this, we developed a multi-scale 3D finite element model, integrating reservoir, and near-wellbore components and applied to an offshore well in China’s ZD Reservoir, an area that has experienced fault reactivations (and casing deformations of wells intersecting reactivated faults) due to routinely water injection in nearby wells. Based on the actual formation’s wellbore-fault angle, a full-size fault is inserted into the model. The traction–separation law (TSL) describes progressive fault damage induced by waterflooding. The model also simulates the impact of fault slippage on cement failure and casing deformation. Research findings indicate that fluid injection reduces friction and shear cementation strength between faults, leading to reactivated fault slippage. The slip process involves three stages: low-level, sharply rising, and high-level stages, each exhibiting reduced fault friction and shear cementation strength. These outcomes provide insights to prevent casing damage during water flooding, optimizing injection points, or using better cement recipes at minimal cost.