Advanced horizontal drilling, multi-stage hydraulic fracturing techniques and other innovative technologies have helped make the Vaca Muerta shale oil and gas resource economically viable. Well Operators developing this resource are continuously revising drilling programs and well designs to better exploit this valuable resource. One option in this development is to increase the length of the horizontal section of each well to add hydraulic fracture stages. This option can potentially increase production significantly with minimal incremental drilling and completion costs. In response to Operator requests, Service Companies are now seeking improved technologies and equipment to enable them to provide more effective service in extended horizontal well environments. Utilizing refined, custom-engineered Coiled Tubing (CT) string designs to perform certain intervention techniques and procedures appear to be an economic and efficient solution in this shale development phase.
Anticipated high-angles in deviated well sections, along with the extended horizontal length of the planned wells formed an expectation that conventional CT designs would not be able to service new well designs. The frictional wall contact force between the coiled tubing and the wellbore, which promotes helical buckling, was greater than the axial compression force limit of the typical coiled tubing designs being used in the area; therefore, a customized taper design was necessary for the expected extended lateral, high pressure wells.
An iterative collaboration between the well Operator, CT Service, and CT Manufacturing Companies took place to purpose-build a CT string design with extended reach capabilities while considering logistics and CT equipment available in the area. An extensive CT string design evaluation, which analyzed tubing forces, downhole buckling, and lock-up behavior in different planned wells, was performed to determine the optimum combination of tubing grade, taper design, wall thickness and section lengths to ensure the likelihood of reaching target depths with adequate weight-on-bit (WOB) for milling operations. Bottom Hole Assemblies (BHA), fluids and cleanout efficiencies were also analyzed in this study.
The use of a proprietary technology from the CT manufacturer facilitated the required wall thickness transitions to strategically place specific thicknesses along the length of the string to enhance force transmission to the end of the tubing, increase strength and stiffness where needed, and reduce fatigue accumulation, and weight.
Field results demonstrated that the use of custom-engineered CT design, extended reach tools and fluid additives, aligned with strict operational practices, has had a great impact on the economics and efficiency of post fracture plug mill-out operations in the Vaca Muerta region. This study documents the improved CT extended reach applications reliability to strategically support this unconventional shale development. Outlined in this study is the evolution of a unique, engineered coiled tubing design, considerations and operation details which helped set and push the limits of extended reach CT interventions, utilizing available CT equipment and technology in the Vaca Muerta shale.