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COPYRIGHT 2005 Hart Publications, Inc.
Deepwater drilling is costly. A spread that includes a floating rig, and related equipment and services, can run to $300,000/day or more. As expensive as drilling time is, however, money spent locating the wellbore at the best position in the reservoir pays big dividends during the field's life.
Well placement and completion design involve critical decisions that have a significant impact on ultimate recovery and lifecycle financial performance.
Putting the wellbore where it will recover the most oil and gas involves decisions made by geoscientists before drilling begins, as well as those made during drilling. The ability to implement those decisions efficiently--even on the fly--expands year after year, driven by a range of developing technologies and the growing expertise of those who apply them.
The latest tools and the best people are critical to drilling wells having 70[degrees] of inclination at depths greater than 18,000ft (5,490m) measured depth (MD) from a floating platform in 5,610ft (1,711m) of water.
Though it had some exploration drilling experience in deep water, Devils Tower was Dominion E&P's first experience with development drilling in such water depths. The learning curve, however, was steep. All but one well came in under budget, and the entire drilling program was completed comfortably below estimated cost. Drilling appraisal wells that could be converted to producers significantly reduced development cost.
The success of the Devils Tower drilling program is more evidence of the ability of Dominion E&P to compete in virtually any technical or economic environment.
In addition to extensive planning, there were several keys to that success, said Craig Castille, supervising offshore drilling engineer:
* careful selection of services and personnel to ensure safety, environmental compliance and efficiency;
* advanced directional drilling, mud and logging technologies that increased drilling speed, hole quality and well placement accuracy; and
* a "technical limit drilling" process that encouraged innovation and continuous improvement.
In the beginning
When Dominion E&P acquired the Devils Tower prospect from Mariner Energy Inc., Well No. 2, which would turn out to be the discovery well, was in progress. Well No. 1 was lost during the "jet-in" process, and Mariner moved to an ocean floor location about 50ft (15m) from the lost hole and began Well No. 2.
Dominion E&P got involved during the discovery well. Well No. 3, the first delineation well, was sidetracked to allow additional zones to be tested and a core to be taken.
Those two penetrations of the reservoirs provided enough information to make it obvious a dry-tree development scheme would be required. Two follow-up wells near the discovery well, a deep test and a well to test shallower zones, were then designed and Noble Corp.'s deepwater rig, Max Smith, was put under contract to drill them.
Knowing that producing wells would be brought to a floating production platform, and to minimize the number of expendable wells, the best location of the wells on the ocean floor was determined. Transponders set on the ocean floor helped pinpoint the well locations to allow proper alignment for the production risers to be brought...
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