Drilling and completion of long, highly deviated, or horizontal wells have become commonplace in most mature petroleum reservoirs, especially for unconventional plays. Field observations indicate that most infill wells pass through depleted zones where stress changes are induced. This often leads to wellbore instability during infill well drilling. The knowledge of equivalent mud weight required can be critical. For reservoir depletion, parent well stimulation and production are key contributing factors. In a previous study (Zheng et al. 2018a), we investigated the critical factors for safe infill well planning caused by production-induced depletion. In this study, we focus on the impact of the stimulation to provide a comprehensive understanding of infill well planning for unconventional reservoirs.
In the previous study (Zheng et al. 2018a), we introduced an integrated reservoir geomechanics coupling workflow using the finite element method. In this study, an improved fracture reservoir coupling technique for fluid leakoff calibration after stimulation shut-in is applied to expand the approach for detailed investigation of fracture stimulation impacts for infill well wellbore stability analysis. The case study is built on a well completed in the Permian Basin to implement the advanced coupling workflow for the induced stress change prediction. Infill well wellbore stability and performance are then analyzed through an uncertainty and optimization workflow to understand the impact of well spacing, drilling time, and formation properties.
Based on the study results, we observe that the safe mud-weight window for drilling an infill well is highly affected by the amount of depletion and the hydraulic fracture geometry, depending on its proximity to the infill well. Under a normal stress regime, the change of stress and increase in differential stress around the wellbore can require us to adjust the mud weight to reduce the likelihood of severe wellbore breakouts and/or mud losses while drilling. For over-pressured formations, pressure depletion, however, tends to reduce the risk of wellbore damage from shear failure. Moreover, the safe mud-weight window can also vary drastically along the lateral landing changes caused by formation heterogeneity and uneven depletion from the hydraulic fracture network.
