Focus on Ancillary Equipment and Fatigue in Coiled-Tubing Deepwater Commissioning

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 25665, “Adaptation of Coiled Tubing for Deep- and Ultradeepwater Commissioning: Focus on Fatigue and Ancillary Equipment,” by François Lirola and François-Régis Pionetti, Saipem, prepared for the 2015 Offshore Technology Conference, Houston, 4–7 May. The paper has not been peer reviewed. The installation of flowlines in ever-deeper and -more-remote areas requires specific technologies for precommissioning. Coiled tubing can be a solution; however, offshore precommissioning can require coiled tubing to be deployed several times for durations sometimes exceeding a month and requires larger diameters. Therefore, a campaign was initiated to characterize the behavior of coiled tubing under combined plastic and elastic fatigue. In addition, an innovative bend-stiffener design was developed to control the stress levels in the coiled tubing at the hangoff location. Introduction Precommissioning is a critical part of flowline installation and operation. This process occurs at the end of the installation to validate the integrity and performance of any system before commissioning. When no direct access is available from a surface facility, precommissioning is, most of the time, performed from a multiservice vessel (MSV) using a flexible line. However, as water depth and the diameter and length of the flowline to be precommissioned increase, the submerged weight of the line becomes an issue, requiring the installation of buoyancy modules to limit the loads transferred to the vessel. To simplify offshore precommissioning activities, the company decided to use coiled tubing. Coiled tubing offers the advantage of having a higher diameter/weight ratio than flexible lines, allowing for large-diameter tubing to be deployed from an MSV while keeping loads transferred to the vessel at an acceptable level. In addition, coiled tubing has an extensive track record onshore and most of the required components are available off the shelf. However, onshore applications of coiled tubing are essentially static while offshore precommissioning activities are dynamic. The coiled tubing hangs from the vessel and, therefore, is subject to loads from the waves, currents, and vessel motions. This means that the coiled tubing and the associated equipment should be designed to withstand extreme loads and elastic fatigue.