Improving Milling Efficiency in HP/HT Unconventional Field by Comprehensive Engineering Design and Strategic Planning of Fracturing Plugs

Abstract

The requirement of tapping new hydrocarbon reserves has pushed the Middle East region to develop its unconventional resources. During the development, longer laterals are drilled to achieve more stages and increase well productivity. This generates more complex intervention activities, including the post-fracturing plug millout with coiled tubing (CT). This study outlines comprehensive evaluation of frac plug milling practices integrated with designing and execution of CT operations to improve overall milling efficiency for these unconventional horizontal wells. Milling optimization was obtained by tackling key enablers of higher efficiency. First, the CT string was precisely engineered to serve the well trajectory and completion size. The tapered wall thickness configuration was strategically planned to maximize stiffness at the highly deviated section while reducing weight on the long horizontal lateral. Plug selection and placement strategy were also meticulously planned to configure the best combination of composite and dissolvable plugs. Since different plug types behave differently during milling, the millout strategy was tailored specifically for each type and their actual downhole environment. The new engineered CT design, coupled with an extended reach tool (ERT), was proven effective in overcoming reach challenges across the long lateral while maintaining sufficient weight-on-bit (WOB) to mill the plugs. The ERT was also observed to enhance milling action due to the vibrations it generated. Those improvements led to faster and smoother operations, resulting in 70% reduction of operating time compared to the baseline established prior to the start of the project. The comprehensive plug placement strategy and better understanding of different plugs behavior in different environments further improved the milling efficiency, as the average milling time per plug was reduced by 80%. Additionally, the reduction in operating time improved the environmental sustainability of the project, as carbon emissions from the CT unit were reduced. The comprehensive engineering design and plug selection strategy delivers significant improvements in millout efficiency. Implementation of key enablers led to performance increase, better resource utilization, and further cost optimization. This achievement also aligns with initiatives to reduce the impact of oil and gas operations on the environment, thus contributing to the goal of achieving net-zero in carbon emission.