Abstract Drilling long horizontal development wells in the conglomerate reservoir of the Junggar Basin, onshore China, has posed significant challenges. Operators have faced various drilling issues including stuck pipe, mud losses, and pack-off events, which impeded development efforts and necessitate the formulation of effective drilling strategies aimed at rapid and safe operations with minimal non-productive time. Understanding the subsurface characteristics of the formation is essential for developing appropriate engineering solutions. To optimize the drilling process, a systematic approach was established by integrating multiple technologies to reduce severe wellbore instability caused by abnormal formation pressures, wellbore collapse, and other complex drilling challenges. This comprehensive workflow consists of three stages: pre-drill modeling and assessment, real-time monitoring, and post-drill validation. The pre-drill geomechanical analysis provides insights into subsurface characteristics of the formation including in situ stress and rock mechanical properties. This information is utilized to optimize mud weights, mud designs, and casing setting depths so as to maintain wellbore stability during drilling. Real-time operations focus on monitoring drilling parameters, cavings, and logging data, offering updated recommendations to field drilling engineers to mitigate wellbore instability. In the post-drill phase, the refined geomechanical model will be used for the optimization of drilling designs for subsequent wells in the area. This paper presents a typical case characterized by a high risk of instability due to several shale intervals in the build-up section and the existence of nature fractures in the horizontal interval which had been known to cause significant wellbore instability. Geomechanical analysis reveals a narrow safe mud weight window in the 6½″ hole section as the collapse pressure in the shaly interval approaches the leakage pressure in conglomerate layers. To enable cost-effective horizontal drilling, a systematic workflow was implemented in the Mahu block, resulting in a 30% improvement in rate of penetration (ROP) and a 32% reduction in wellbore instability related drilling issues compared to offset wells in the same field that were drilled without a risk mitigation strategy. The systematic approach not only effectively reduced drilling hazards related to wellbore instability but also significantly increased ROP. With the attainment of major flat time reduction and lesser rock failures, borehole quality had been improved. However, the effective application of this systematic method requires ongoing learning and refinement. Continuous improvement necessitates regular updates to the geomechanical model as further data and insights are gathered in the Xinjiang Oil Field.
Wang et al. (Mon,) studied this question.
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