Lessons From Integrated Analysis of GOM Drilling Performance

Abstract

Summary Offshore drilling continues to be extremely cost intensive, with U.S. $50 million wells not uncommon. This paper discusses one company's experience and the lessons it learned from a comprehensive analysis of Gulf of Mexico (GOM) historical data for drilling-performance benchmarking and continuous cost reduction. Drilling operations were broken down into discrete activities, and the best times from all the wells—including trouble time—were aggregated to form the "best composite time" (BCT). The BCT, introduced in recent papers,1–3 was applied, along with learning-curve analysis and other investigative tools, to examine drilling problems and the lessons learned to capture the best practices and, there by, challenge well-planning and construction practices. The "best composite cost" (BCC), or the monetary equivalent of the BCT, was also calculated and used for well-cost benchmarking. Correlative analyses of the wells (i.e., crossplots of drilling events along side mud-log data, wireline logs, and geologic data) were used to elucidate major well problems and abnormal flat times that caused deviations from the BCT. Correlative analysis also helped explain why some wells were drilled relatively trouble-free, even in difficult environments. From a more detailed trouble-time analysis of company-operated wells, tool/equipment failure was seen as a significant trouble-time component. Major drilling problems were also found to be mostly well-pressure related (e.g.,well control, lost circulation, and stuck pipe), supporting increased emphasison improved planning and quantification of equivalent circulating density(ECD), deepwater geopressures, and narrow drilling margins, especially in ultradeepwater environments. Overall, the company's 2003 trouble time was 26% of the total drilling time from spud to rig release. The BCT/BCC methodology is actually one element of "The Ten-Step Process" discussed exhaustively in Refs. 1 and 2. Applications to two onshore areas, so far, have shown encouraging results in drilling-costreduction. Applications to more-complicated offshore GOM wellbores, cost components, and narrow geopressure margins are the focus of this paper. The fields investigated are located in different parts of the GOM (Table 1). For brevity, results are shown only for the subsalt area of South Timbalier, the deepwater Green Canyon (GC) area, and the ultradeepwater eastern Gulf of Mexico(EGOM).