Integrated wellbore stability analysis for well trajectory optimization and field development: the West Kazakhstan Field

Abstract

Severe wellbore-stability issues such as stuck pipe, sidetracking of wells and incomplete pipe-conveyed-logging operations have been encountered during drilling horizontal wells in the West Kazakhstan Field. To contribute to solutions of these issues, an integrated wellbore-stability study was implemented to effectively plan the future drilling operations in the West Kazakhstan Field, to maximize the drilling margin for the future wells drilled, and to optimize the future field development. Typically, only a rock mechanics component for wellbore-stability analysis has been used to obtain wellbore-stability numerical models. In this study, however, the rock mechanical model was coupled with the mechanical stress, temperature alteration, shale-fluid physicochemical interaction, and the flow-induced stress using the Mohr-Coulomb and Mogi-Coulomb failure criteria. The problem diagnosis is a very important part of any wellbore-stability analysis. A special wellbore-stability problem-diagnostic scheme was first used to identify problematic horizons. The possible causes of the wellbore-stability issues were narrowed down. The well trajectory, drilling-fluid density, and types of water-based mud were confirmed to have a dominant impact on the occurrence of the wellbore-stability problems in West Kazakhstan Field. Dipole sonic, imaging, and sonic scanner logs were utilized to obtain in-situ stresses and formation properties. The strike-slip regime was identified in the study field. Pore pressure was predicted in the interest intervals within the West Kazakhstan Field utilizing the Eaton method with significant modifications of the Eaton's compaction coefficients. The stochastic risk and sensitivity analysis was conducted to evaluate the sensitivity of the obtained input data on the study outcome. The Mogi-Coulomb formation failure criterion was found to be a better characterization of the brittle rock failure in the West Kazakhstan Field as utilization of the Mohr-Coulomb failure criterion resulted in overestimation of the wellbore collapse pressure, probably due to ignoring the strengthening effect of the intermediate principle stress. The results of this study could benefit the mitigation and/or prevention of wellbore-stability issues in the West Kazakhstan Field.