Lessons Learned from Integrated Analysis of GOM Drilling Performance
Authors: Iyoho A.W. , Meize R.A. , Millheim K.K. , Crumrine M.J. 
Published: October 2008

Abstract
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 (Table 1). For brevity, results are shown only for the subsalt area of S. Timbalier, the deepwater Green Canyon (GC) area, and the ultra-deepwater Eastern Gulf of Mexico (EGOM).

Background
Over the past thirty years, reservoir engineering has successfully evolved well-test analysis, and production engineers have developed nodal analysis as a core technical area. Both sub-disciplines have greatly enhanced petroleum technology. To our knowledge, drilling engineering has not formalized tools and processes that would unambiguously constitute drilling analysis, despite the fact that drilling operations routinely generate large amounts of data. While millions of dollars are spent on collecting and storing daily drilling data, industry continues to struggle to establish how best to utilize the data. In some cases, the data are seldom revisited or are under-utilized for drilling cost control. How much resources are committed to collecting and storing data, and how much to actual data analysis for improving drilling performance? In our opinion, the industry focuses too much on amassing a myriad of drilling-related data and not nearly enough on actually applying this information to capture lessons learned as well as operational best practices to benefit well design and construction. In this follow-up paper, historical GOM drilling data, properly QC'd into a knowledge-base system, were analyzed as discussed in Refs. 1-3.