Managing Wellbore Instability in Geologically Complex Field of Indian Offshore

Abstract

Abstract This paper addresses the challenges encountered during the drilling of horizontal and multilateral wells in the geologically complex Western offshore field of India. The Operator has been actively engaged in drilling such wells since the late 1980s. The primary objective is to effectively manage wellbore instability issues, specifically those arising at inclination exceeding 50 degrees, which have resulted in recurrent severe tripping issues leading pack-off, stuck pipe events and lost-in-hole incidents. The scope of this study encompasses a comprehensive analysis of the causes of wellbore instability. The general casing policy in this field involves using a Synthetic oil-based mud system (SOBM) to cover Carbonate and Shale formations. However, drilling challenges arise when inter-bedded formations are exposed at high angles, significantly complicating the wellbore. Through a detailed analysis of stuck pipe incidents, down hole conditions, BHA details, and well profile, identified the high risk for wellbore instability. Innovative solutions were implemented, using high-tech Image logs to identify geo-mechanically stressed high risk drilling direction, the establishment of an optimal mud weight window, and the introduction of an Under reamer to mitigate tight hole conditions. The implementation of these measures proved highly effective in handling the geo-mechanically unstable formation. Adjustments to the casing seat were made to cover potential loss areas in the upper section of the Carbonate formation. Improved Drilling Practices through Real time Monitoring were instituted to mitigate frequent back reaming and potential complications. As a result, non-productive time (NPT) and down hole complications were significantly reduced, culminating in zero cases of lost-in-hole incidents in the 2023-24 drilling season. These outcomes are pivotal for overall well cost control and contribute to the successful targeting of zones, showcasing the practical significance of the proposed solutions. This paper introduces innovative approaches to address wellbore instability, notably the utilization of high-tech Image logs and the application of an Under reamer to overcome the geo-mechanical stress issues. The emphasis on detailed analysis, data-driven decision-making, and the integration of casing adjustments, mud weight optimization, and drilling practice improvements offers a comprehensive and novel strategy for mitigating wellbore instability in a geologically complex field. The presented insights contribute valuable additions to industry best practices, demonstrating the adaptability and efficacy of tailored solutions in addressing specific drilling challenges.