One of the largest components of the cost of deepwater (greater than 1,500 ft water depth) subsea developments is the day-rate of the drilling rig spread, combined with the substantial costs of the normally required installation tools and other equipment that must be installed on the rig during completion work. In an effort to reduce these substantial capital costs, Shell has used several combinations of drilling vessels (mobile offshore drilling units - MODUs) and construction vessels over the past several years and has rented and in some cases purchased some specific pieces of equipment. Shell has also studied the entire completion process thoroughly, identifying opportunities for improving effiency and eliminating all but essential activities. These efforts have proved worthwhile, saving literally millions of capital dollars over four most recent major subsea projects in the Gulf of Mexico and promising to greatly improve the profitability of its future subsea projects.
Shell began estimating the costs of the first deepwater subsea developments in the early 1990s and several portions of the cost areas were highlighted for immediate further study. As these study efforts grew, standardization of subsea equipment and value engineering quickly began to show promise, but it was evident that this would require a substantial investment of time and considerable cooperation from the leading industry suppliers. However, investigating the more efficient use of existing equipment -- such as the MODU spread itself and improvements in the design/use of the existing equipment that have been historically required during well completions -- promised immediate substantial savings. After its initial experiences with Tahoe, 1,500 feet water depth (fwd), Popeye, 2,040 fwd, Mars, 2,900 fwd, and Mensa, 5,200 fwd, Shell continued its focus on improving the profitability of subsea developments, capturing the learnings from these projects and applying them to the early planning stages of the next group of subsea projects.
Specifically, Shell concentrated its efforts at several specific targets, such as:
Efficient utilization of the MODU on location (deck layouts, subsea tree handling equipment capabilities, interfaces with completion tools/equipment)
Proficient use of existing tools and procedures ("Technical Limit Completion" exercises)
Development of new more efficient tools (more efficient completion riser designs, use of a larger winch for lowering subsea equipment packages to the seafloor, a subsea-releaseable blowout preventer [BOP] funnel)
Overall technical review of the entire completion process (unloading the well to the pipeline, instead of conventionally unloading to the rig)
This paper will present the results of the work in these target areas, highlighting the successes and describing in detail the extraordinary breakthrough engineering ideas that surfaced during this effort.
Shell completed its first Tahoe deepwater subsea development project utilizing 4th generation MODUs built in the mid-1970s. The next several subsea projects utilized similar MODUs with variable deck loads averaging from 3,000 tons to 4,500 tons. With the Popeye and Mars subsea wells at 2,040 fwd and 2,900 fwd, respectively, deck space was already a critical issue, along with limited crane capacities for lifting the required equipment onto the rig from supply boats.