Lessons From Integrated Analysis of GOM Drilling Performance

Abstract

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).

Computer simulation of dragging with rotation of a drill string in 3D inclined tortuous bore-hole

“…The efforts to simulate the inclined drill problems with the use of computer models present considerable difficulties determined by a number of factors [5,11,12,14,15,17]. Among them the relatively complex geometry of the drill string is the main concern.…”

Modeling the Energy-Saving Regimes of Curvilinear Bore-Hole Drivage

“…It was founded on the theory of flexible curvilinear rods constituting the stiff-string drag and torque model. The world statistics indicates that the accident rate is one in three for driving bore-holes of this type [23,24]. In the second case, all geometric parameters of the bore hole axis can be calculated after their approximating by spline interpolations.…”

The computer simulation of drill column dragging in inclined bore-holes with geometrical imperfections

“…Taking into consideration that lengths of the modern curvilinear bore-holes are planned to approach 15 km and their costs exceed $60 million, it can be concluded that the problem of computer simulation of the drill column behavior is very urgent. At the same time the efforts to solve it present considerable difficulties determined by a number of factors (Iyoho et al, 2005). Among them the large length of the DC is the main one.…”