The procedural development implemented across an unconventional project in Middle East is explored, delving deeper into coiled-tubing (CT) design, from metallurgical properties and string specification to bottomhole assembly (BHA) and fluid selection, tailored to plug-and-perf operations involving the use of a specialized frac plug. Further discussed is the "learning curve" generated, highlighting improvements achieved across the "iron triangle" of operating time, cost, and quality, referring to case studies of interventions conducted across multiple horizontal wells.
Unconventional CT interventions have always been challenged by an operator's quest to drill the longest possible lateral to maximize per-well estimated ultimate recovery (EUR) by maximizing the number of fractured clusters/stages. CT job designs across these projects usually rely on running the biggest outer diameter (OD) CT with the largest hydraulic downhole motors available to enable the deepest reach, highest weight on bit (WOB), torque, and circulation rate. However, this conservative approach causes operations to be overdesigned, ultimately resulting in excessive operational cost and nonproductive time. As observed from this experience, an engineered process enables an operator to select the correct resources to meet the operational objectives.
A successful multiwell campaign of prefrac-drift, wellbore fluid displacement, cement sheath cleanout, followed by tubing-conveyed perforation (TCP) and post-frac 32–44 plug millout was performed across high-pressure/high-temperature (HP/HT), sour, unconventional wells in Middle East. After respective CT interventions, the wells were successfully fractured and flowed back. Based on lessons learned and various corrective action items implemented, service efficiency (single run) and job time (+50% reduction) were substantially improved. This enhancement was mainly attributed to the revised surface piping and instrumentation (P&I) rigup, CT material and dimension selection, BHA components, including custom-built mill/motor and extended-reach vibrating tool, gel and friction reducer fluid placement, reduced wiper trip frequency, etc.
These optimized CT interventions created a more balanced approach to unconventional operations, wherein bigger is not always better. The CT procedure evolved, initially referencing best practices from analogue unconventional plays, while slowly progressing into a tailored fit-for-purpose operation. This approach enabled the operator to achieve operational objectives more efficiently.