Setting New Milestones for Coiled Tubing Intervention in Mega-Reach Wells

Abstract

Maximizing reservoir contact through extended-reach and mega-reach wells has become a prevalent field development strategy for major offshore operators in the Middle East. This is especially true for the giant oilfield "A", where drilling targets go beyond 40,000 ft. measured depth (MD), with MD/TVD ratios in excess of 4.5:1. Such challenging horizons call for a detailed re-evaluation of well interventions. In 2019, the well surveillance program in the field A required intervention in a mega-reach well with a MD over 35,500 ft. and 4.5:1 MD/TVD ratio. This reach was unthinkable only a few years ago but has been made possible thanks to several recent key technological advancements, such as coiled tubing (CT) equipped with optical fiber and new CT hydraulic tractors, proactive and detailed planning during the drilling phase, the development of highly engineered CT string designs, surface equipment upgrades, and accurate software modeling. The target well is an oil producer with horizontal section beyond 23,000 ft., completed with 6 5/8-in. pre-perforated liner and 23 swellable packers placed across the 8 1/2-in. open hole section. A multiphase production logging tool was selected to assess the production profile along its horizontal drain. With a target depth beyond the reach of conventional wireline, CT equipped with optical fiber emerged as the optimum solution to facilitate reach and overcome the weight and pumping limitations of wired CT. A comprehensive CT reach modeling exercise compared the performance of several 2-in. and 2 3/8-in. CT string designs and identified operational requirements and reach gains from CT hydraulic tractors. As a result, an engineered 2-in. CT tapered string of near 36,700 ft. was developed, capable of being equipped with optical fiber line, while delivering the required flow rate and differential pressure to the CT hydraulic tractor without compromising any operational safety margin. At the time of manufacturing, this was considered the longest CT string ever produced and fitted for downhole telemetry. The operation itself set new records for well interventions in mega-reach wells, with a CT reach above 35,500 ft. MD, including a hydraulic tractoring footage over 15,650 ft. MD with spaced slugs of chemical friction reducer. This case study explains how to develop a safe, robust, and effective solution to mega-reach well challenges using the CT-conveyed optical fiber telemetry technology in one of the deepest wells in the field A, setting a new global record in CT reach. The lessons learned are now the reference for other operators in the Middle East and across the globe for performing interventions in wells that continue to be stretched in its extended reach. It also depicts why telemetry through optical fiber is key to the success of such projects and provides an overview of technology needs for the future of mega-reach well developments.