Hydraulic fracturing induced fault slip and casing shear in Sichuan Basin: A multi-scale numerical investigation

Abstract

A multi-scale numerical investigation for fault slip and casing deformation is carried out by combining a large-scale distinct element model to simulate the hydraulic fracturing and fault slip and a small-scale finite difference model to analyze casing deformation. The result of large-scale model shows that the pore pressure elevation causes the slippage of fault and thus the deformation of an intersected wellbore and casing. Both fluid viscosity and injection rate have significant impacts on the shear displacement while the effect of injection volume is determined by the number of natural fractures in the reservoir. The result of small-scale model shows that the fault sliding causes the stress concentration near the fault plane and thus gives rise to the casing yielding. Casing grade, casing sheath thickness and cement sheath thickness have limited impacts on casing deformation while the countermeasure of no cementing is effective on mitigating casing deformation. Moreover, optimizing the well trajectory can help to decrease casing deformation. The field data in Sichuan Basin demonstrates that decreasing the injection rate could effectively mitigate the casing deformation. But the effect of total injection volume is less significant probably due to the fact that the shale reservoir is intensively fractured.