A Silent Killer: Capturing The Learnings of Unexpected Casing Deformation - A Case History from Block-61 Tight Gas Field

Abstract Throughout its life, every oil and gas well is subjected to many risks with potential detrimental consequences affecting reserve accessibility and resulting in expensive corrective intervention activities. One of those risks threatening wells health is Casing Deformation (CD). CD are notoriously difficult to detect real time, and normally discovered after the fact during subsequent operations. Therefore, understanding of the interdisciplinary context and early symptoms associated with CD is crucial to minimize their occurrence. The objective of this paper is to discuss a CD incident that took place in one of the wells – G-107 in bock-61, describing its silent signature and lessons learned for future field development and production enhancements. Successfully minimizing, managing, and recovering from CD incidents heavily depend on understanding the geomechanics and geologic context associated with a specific field, the data acquisition and processing of diagnostic tools used, and on well architecture and stimulation design and selection. Additionally, proper operational planning is also critical in reducing and mitigating the economic impact of CD when they occur. Block-61 is considered one of the biggest gas fields in Oman. Production is mainly from Barik and Miqrat sandstone formations with Barik as the main reservoir. Most of the wells are vertical and few horizontals. On 20 November 2022, after the hydraulic fracturing operation and during bridge plug milling operation in G-107, a restriction was encountered at the top of the perforated interval. Through the application of different diagnostic tools, the restriction was later determined to be a casing ovalization with a minimum cross well diameter of 3.18 in., preventing accessibility to the rest of the well and the associated reserves. The paper will review the incident investigation approach adopting the five whys methodology, including documentation of the findings and learnings, highlighting the gaps associated with well planning, well architecture and stimulation design, and all the ancillary operations such as perforation. Furthermore, it will describe how difficulties in retrieving records of previous CD incidents should be corrected and not underestimated. A detailed description of the diagnostic tool selection such as downhole camera, multi-finger caliper logs and lead impression block, and the analysis of the data acquired with such diagnostic tools will also be presented. Finally, recovery actions and future changes to the well design will be described aiming for a robust system that does not simply react to the incident but allows mitigating future CD events.