Summary Offshore drilling continues to be extremely cost intensive, with U.S. $50million 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, 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, thereby, 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 alongside 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 emphasis on 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-cost reduction. 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).

Offshore drilling continues to be extremely cost intensive where $50-million wells are not uncommon. This paper discusses one company's experience and lessons learned from a comprehensive analysis of Gulf of Mexico (GOM) historical data for drilling performance benchmarking and continuous cost reduction. The "Best Composite Time" (BCT) introduced in recent papers (Refs. 1-3) was applied along with learningcurve analysis, and other investigative tools to examine drilling problems and lessons learned, capture best practices, and thereby challenge well planning and construction practices. Drilling operations were broken down into discreet activities and the best times were aggregated to form the BCT.The "Best Composite Cost" (BCC), the dollars equivalent, was also calculated and used for well-cost benchmarking. Correlative analyses of the wells, i.e. crossplots of drilling events alongside 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 component. Major drilling problems were also found to be mostly well-pressure related (well control, lost circulation, and stuck pipe), supporting increased emphasis on improved planning and quantification of ECD, deepwater geopressures, and narrow drilling margins, especially in ultradeepwater environments. Overall, the company has been able to reduce the trouble time to only 16% of total time in 2003.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 cost reduction. Applications to more complicated offshore GOM wellbores, cost components, and narrow geo-pressure margins are the focus of this paper. Fields investigated are located in different parts of the GOM

Subsalt wells are notorious for drilling difficulties encountered while penetrating both the salt and adjacent shales. Slow penetration rates, poor hole integrity, lost returns, bit balling, and pack-off problems are typical in these formations.After experiencing a number of these problems when using a conventional saturated salt mud to drill a Gulf of Mexico discovery well through a salt formation, one major operator switched to a synthetic invert-emulsion fluid for the subsequent delineation well. Both wells penetrated approximately 8,000 feet of salt to reach total depth (TD). However, performance improvements resulting from use of the synthetic fluid in the second well reduced drilling by 78 days, generating an estimated savings of $12 million. In addition, the second well included a record bit run of more than 10,000 feet. This paper describes the drilling programs used in the two wells, recounts drilling performance, and discusses the savings achieved.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper discusses one-company's experience in drilling a number of wells in 4000 to 9000 ft of water depth (WD) in the Gulf of Mexico (GOM), from the technical as well as the managerial aspects of this massive undertaking. The paper lists and discusses technologies, successes, and challenges experienced under the following headings:• Differences in technology from one area to another, as well as challenges and solution ideas to minimize trouble and flat time; • Scheduling and impacts of rig contracting, along with timing and execution; • Technical support by way of historical data analysis, benchmarking, lesson feedback into well planning and construction, and knowledge management and knowledge retention (where new technical staff are easily and quickly brought up to speed); • Mud engineering and special drilling muds -both water-based mud (WBM), and synthetic-based mud (SBM) are shown to be crucial to environmental compliance, cost control, and trouble mitigation depending on the area; • Hydraulics and cementing issues -modeling and validation, along with special considerations for the application of PWD (pressure while drilling), and other real-time data; • Technical challenges still to be addressed, and the way forward; and • Managerial challenges still to be addressed, and the way forward.