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 nonviscous 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.

This paper describes three coiled tubing (CT) applications in depleted reservoir wells, where full circulation and precise fluid placement were achievable only by using a novel solids-free loss-control system, such as abrasive perforating applications. It also describes the preparation work, such as laboratory results and mixing procedure performed to ensure successful implementation. The analysis of Ukrainian reservoir conditions by local and global engineering teams showed that in a highly depleted well, abrasive jetting through CT was the best option to efficiently perforate the wellbore. However, this approach could lead to later impairment of the gas production if the abrasive material (sand) could not be entirely recovered. Such a risk was even higher as wells were depleted and significant losses to the formation occurred. The use of solids-free fluid-loss material that was easy to mix, pump, and remove after the operation, was, therefore, critical to the success of that approach. In Ukraine, most of the brownfields have a reservoir pressure that varies between 50% and 20% of the original reservoir pressure. This is a challenge for CT operations in general and especially for abrasive jetting, which requires full circulation to remove solids. It also complicates intervention when precise fluid placement control is required, such as spotting cement to avoid its being lost into the formation. The perforation solids-free loss-control system is a highly crosslinked Hydroxy-Ethyl Cellulose (HEC) system designed for use after perforating when high-loss situations require a low-viscosity, nondamaging, bridging agent as is normally required in sand control applications. It is supplied as gel particles that are readily dispersed in most completion brines. The particles form a low-permeability filter cake that is pliable, conforms to the formation surface, and limits fluid loss. The system produces low friction pressures, which enable its placement using CT. Introduction of that system in Ukraine allowed the full circulation of sand or cuttings to surface without inducing significant damage to the formation for first time; it was also used for balanced cement plug placements. This project was the first application of the solids-free loss-control system in combination with CT operations. It previously was used only for loss control material during the well completion phase in sand formations with the use of drilling rigs.