Development and Qualification of a Subsea 3,000 Barrel Pressure Compensated Chemical Storage and Injection System

Abstract

Abstract This paper presents important findings while executing a detailed qualified design of a large (3,000 + barrel), subsea (to depths of 10,000 fsw) production chemical storage and injection system. The design drivers for the system were safety first, extensive utilization of existing commercially available equipment / tools / methods, and a re-usable shuttle system that allows for delivery of production chemicals as a service versus the current approach where an operator / owner makes a capital investment. The system is designed to be compatible with existing production chemical formulations and features multiple barrier design between the chemicals and the environment. Placement of the storage and injection system directly on the seafloor in close proximity to the point of need eliminates expensive chemical umbilicals, removes significant topside chemical storage and injection kit weight and space requirements at host facility and isolates hazardous chemicals from platform workers. The re-deployable shuttle economically allows inspection, repair and maintenance to take place quayside with the ability to upgrade equipment as technology progresses and / or quickly and cost effectively adjust to ever-changing field requirements. Subsea wells have been proliferating over the last decade with ever-longer tie-backs to enable commercial recovery of small resource pools that are unable to support a traditional floating system development. Virtually all wells, especially subsea, require various volumes and types of production chemistries during their operational life. For subsea wells, the incumbent technology is chemistry delivery via umbilicals. In rare occasions, small volumes are sometimes delivered via single trip, disposable containers, principally during intervention activities. As tie-back distances have increased, so have the technical challenges with their attendant mushrooming costs. These challenges include the needs for; special corrosion resistant materials, resistance to high pressures differentials, material flexibility and ‘crimp – resistance’, and long term reliability. Additionally, some of these chemicals are high viscosity and as the tie-back distances increase, so does the pressure drop of the flowing fluids. In some cases, the risks of plugging and the magnitude of the delta-pressure drop in ½? – ¾? chemical tubing within the typical umbilical can preclude tie-backs of long offsets from the host / hub facility. The subject system overcomes many of these challenges by locating a large, pressure compensated storage and injection facility directly on the seafloor in close proximity to the point of need, thus qualifying it as enabling technology for extra-long tie-backs and enhancing technology for short tie-backs, de-bottlenecking, or early production system usage.