The use of coiled tubing service in the shale market has been of great importance in the process of preparing O&G wells for production, mainly in the post-fracturing isolation plug milling and solids cleanout. The challenges that the coiled tubing (CT) industry has been facing are substantial and range from CT pipe manufacturing and related technical matter to logistic and operational conditions. The CT industry has worked relentlessly to remain competitive both in efficiency and economic terms in comparison with new competitive completion techniques.
Well cleanouts are by far the most common operation performed with coiled tubing on a worldwide basis and also one of the most complex operations due to the large amount of operational variables involved. The shale market experiences the very same scenario, and cleanout-milling activity is far from flawless. Substantial amounts of solids, mainly the heavier ones, remain in the wellbore after the cleanout operation is completed.
Some of the traditional and deeply rooted techniques utilized in well cleaning nowadays have their origins in drilling and work-over operations in vertical wells. Some new important techniques presented in this paper, primarily addressing operations in horizontal shale wells, helped to improve overall efficiency during cleaning-milling operations.
These new techniques involved advanced cleanout procedures coupled with the utilization of non- viscous fluids throughout the operation. Use of viscous fluids was completely eliminated from the operations and even for contingency plans in critical scenarios, such as high-drag or near-stuck conditions. When most of the wellbore clean out parameters were optimized, hole-cleaning performance was significantly better when eliminating viscous pills and controlling the chemical dosage.
This paper also describes the importance of proper plug milling/well cleanout and how this was attained. As milling and cleanout procedures have a direct influence on each other's performance, it is imperative first to optimize each one to maximize overall performance.
Likewise, other operational aspects are discussed here such as the importance of RIH/POOH speeds, bottom-hole assemblies (BHA), the effect of proper formation balance on the overall results and also the advantages of using non-viscous fluids from logistic, economic and environmental viewpoints.