This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 184752, “Vaca Muerta Coiled-Tubing-Operations Success and the Development of Future Extended-Reach Operations,” by I.I. Galvan, Global Tubing; M.M. Nebiolo, R.D. Del Negro, and G.A. Landinez Gomez, YPF; C. Cerne, SPE, ThruTubing Solutions; and A. Sanchez, SPE, and G. Mallanao, Global Tubing, prepared for the 2017 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, Houston, 21–22 March. The paper has not been peer reviewed.
Advanced horizontal drilling, multistage hydraulic fracturing, and other technologies have helped make the Vaca Muerta shale oil and gas resource economically viable. An option to exploit this resource better is to increase the length of the horizontal section of each well to add hydraulic-fracture stages. Anticipated high angles in deviated well sections, along with the extended horizontal length of the planned wells, formed an expectation that conventional coiled-tubing (CT) designs would not be able to service the new well designs. Using refined, custom-engineered CT-string designs appears to be an economic and efficient solution.
Project Overview
Increased diameter, strength, and reliability have made CT the preferred cost-effective well-intervention solution in the Vaca Muerta unconventional shale development; however, the maximum lateral reach the CT can achieve during operations is a limiting factor for well optimization.
Initially, 2-in. CT strings with a simple wall taper shape were an effective and reliable option to complete wells in the first development stage. However, the need for optimized design and even-larger-diameter CT with enhanced-wall-thickness configurations became apparent when an increase of the well lateral lengths was attempted.
CT-String Design Considerations
The CT-string designs followed a cooperative process between the operator, the CT service companies, tool providers, and the CT-manufacturing engineers. Tubing forces, buckling occurrence, and lockup depths were analyzed in detail to determine the optimal CT size and string design makeup to ensure the likelihood of reaching target depth (TD) in the planned extended-reach wells. Additionally, hydraulic analysis was performed to compare frictional pressure losses (CT, bottomhole-assembly, and annular) using the optimal flow rates for annular velocities adequate to support sufficient well cleaning. The results from the analysis were used to estimate fatigue accumulation in the CT strings, considering anticipated circulating pressures and surface-equipment (reel and gooseneck arch) dimensions.
The primary objective for the new CT-string design is to optimize lateral reach and available weight on bit for post-fracture mill-out operations.
