Gulf of Mexico Deepwater Platform Decommissioning

Abstract

Abstract There are currently 63 fixed steel platforms in the Gulf of Mexico (GoM) in water depths greater than 400 feet. Most of these platforms will have jacket weights in excess of 10,000 short tons. In the context of this paper, the aforementioned parameters define deepwater platforms. Any of these platforms would set a new GoM decommissioning record in terms of size and depth. A number of these platforms have been identified and are being planned for decommissioning within the next few years. Assessing the relevant technology for decommissioning and its resulting cost is a challenge for all concerned. Offshore platform decommissioning is a challenge under any circumstances in terms of planning and executing the work in an environmentally sensitive, safe, and economical way. Among the issues that must be faced are limited availability of equipment and the capability of current technology to adapt to the depths faced in deepwater. This paper presents the potential issues (resources, technologies, and methodologies) that may be encountered in decommissioning deepwater platforms. Fixed conventional platforms in water depths greater than 400 feet are identified and summarized. GoM platform removals case histories are presented to show the various decommissioning options executed to date. The paper concludes in summarizing the regulatory environment that will affect the decommissioning of deepwater platforms. Introduction Table 1 summarizes the GoM fixed steel platforms in water depths greater than 400. Most of these platforms are selfcontained multi-well drilling and production. Early installations are in a six to eight leg configuration. Later designs such as Pompano (VK 989 A) reduced the legs to four, but added multiple skirt piles around each leg. Platforms such as ST 192 A and SP 89 E were designed as a junction between deepwater developments and shallow water pipeline transmission systems. As shown in Figure 1, the deepwater platforms lie near or outside the continental shelf with a greater concentration in Louisiana waters. The orange outlined areas in Figure 1 are the designated artificial reef sites that are managed by either the Texas Parks and Wild Life Department or the Louisiana Department of Wild Life and Fisheries in the western and central planning areas. The decommissioning options available for deepwater platforms are the same as those in shallower shelf platforms. Figure 2 shows the overall production facilities, deck and jacket disposal options. In general all options executed take the production facilities and decks to shore for storage or disposal. The underlying difference is the fate of the jacket. The Complete Removal option takes the conductors and jacket to shore for disposal or storage for future reuse. Remote Reef options assumes that the conductors are removed and disposed onshore and the jacket rigged, lifted, towed and placed at a remote artificial reef site. Topple in-Place is where the jacket and conductors are pulled over into a horizontal position and toppled creating an artificial reef site.