Mitigation of wellbore instability in deviated wells by using geomechanical models and MPD technique

摘要

During drilling operations for the E oilfield in the Mishrif formation in southern Iraq, stuck pipe presents a significant wellbore stability problem for deviated wells. In this study, two solutions are utilized to address this problem. The first approach is a 1-D Geomechanical model of the Mishrif formation compiled based on the state of stress and rock strength parameters. It is utilized to assess the contribution of borehole collapse leading to the stuck pipe problems. The results of this study show that wells characterized by stuck pipe are drilled along azimuths which promote wellbore collapse. Three different failure criteria, the Mohr-Coulomb, Mogi-Coulomb, and Modified Lade rock failure criteria, are investigated to determine feasible drilling trajectories and mud pressure conditions for many different wells in the Mishrif Formation. If a specific azimuth for a well cannot be altered, an optimum inclination is recommended to reduce the severity of the borehole collapse. However, the optimum drilling inclination progressively changes as the intermediate principal in-situ stress increases. The second approach is evaluating the feasibility of using the managed pressure drilling (MPD) to optimize the drilling process by controlling mud weight while applying required surface pressure to achieve the target bottom hole pressure (BHP). DZxION CSM software simulation uses different mud weights to determine required choke surface backpressure (SBP) to achieve the initial target equivalent circulation density (ECD). This study discusses hydraulic simulation software used to model the drilling development plan. The software optimizes MPD parameters and discusses the sensitivity effects of each parameter on wellbore pressure and provides guidelines for managing pressure by adjusting these variables.