Effect of local loads on shale gas well integrity during hydraulic fracturing process

The shale slip, cement failure and micro annulus caused by hydraulic fracturing in shale gas well may generate local loads which have significant effects on the stress status and yield of the casing. Local loads are considered in the well integrity analysis based on the Mechanics of Materials. A mechanical model is established for the casing behavior under local loads. The accuracy of the model is verified by numerical simulation, Nesrter's method and field data. The effects of local loads and casing dimension on the casing failure are illustrated by the sensitivity analysis. The analysis results show that the casing collapse is more likely to occur under the radial local loads than under parallel ones. Increasing casing thickness and decreasing casing outer diameter are in favor of reducing the casing failure in shale gas wells. The local loads region has the greatest effect on anti-collapse strength of the casing when φ = 90°. Through decreasing the wellbore diameter of shale gas wells and intersecting the natural fractures of shale gas reservoir reasonably, the directional drilling safety, cementing quality and well integrity can be effectively improved, and the casing deformation can be much reduced.