Wellbore Optimum Stability of Oil Well Drilled in a Highly Fractured Carbonate Reservoir Based on Dipole Sonic Analysis

Abstract

Wellbore stability is dominated by in-situ stress and geomechanical parameters of formation rocks, so estimating these parameters around the wellbore is important. The studied well is a suitable candidate for investigation of wellbore stability due to continuing directional drilling and planning for oriented perforation and hydraulic fracturing program from the wellbore and availability of dipole sonic, nuclear magnetic resonance (NMR), core image, and log data to optimize and estimate wellbore stability conditions. In this study, the rock permeability is derived from dipole sonic analysis to investigate the certainty of the model; these results are compared with NMR and special core analysis results. Then, based on these results, pore pressure, in-situ stress, rock mechanical properties, stress and fracture distributions, and anisotropy of formation are calculated and compared with Image log Results. Finally, the optimum mud weight to avoid wellbore failure can be estimated from all these data. As the final results, the maximum horizontal stress direction is N33E, and most open fractures are in this direction. The minimum horizontal stress direction is in N57W, and the safe and appropriate mud weight is between 6.5 and 7.5 ppg, which can be considered 7 ppg. This technique is based on dipole sonic analysis that can be applied to investigate wellbore stability in intervals with no core or image log analysis.