Abstract
Casing failure during hydraulic fracturing is infrequent, but its consequence and impact can be significant for the shale gas wells. It may result in inaccessible cased hole and environmental and safety concerns over wellbore integrity during the shale gas reservoir development. Based on theoretical analysis, numerical simulation and field measurement, the failure mechanisms of casings in shale gas wells are revealed. Through parametric sensitivity analysis, the countermeasures are recommended. Results indicate that one of the casing failure mechanisms in shale gas wells is shear deformation induced by the slip of shear fractures. The simulated casing deformation is consistent with the lead impression. Casing curvature is introduced to assess the traveling capability and casing integrity. The maximum curvature is significantly larger than that of normal directional borehole, which causes the resistance of downhole tools passing through casing. Decreasing the crossing angle and employing the cement with a low Young's modulus or even no cementing can be the effective measures to prevent casing failure in this mode. The research findings provide new evaluation criterion and controlling methods for casing integrity in shale gas wells under hydraulic fracturing.
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