Summary
Oil and Gas Journal reported a successful appraisal well drilling by BP PLC. This well was drilled in a previously untested southern segment of Mad Dog field in the Gulf of Mexico. The 826-5 well was drilled on Green Canyon Block 826 about 100 miles south of Grand Isle, La. The well found 280 net ft of hydrocarbons in the objective Miocene hydrocarbon-bearing sands. In 2008, BP drilled the A-7 well in the western part of the field, with 275 ft of net pay.
Analysis
BP with its partners BHP Billiton and Unocal (now Chevron) discovered Mad Dog field back in 1998. It came on stream early 2005. This large field spans seven Green Canyon GOM blocks: 738, 781, 782, 783, 825, 826, and 739. It is a deep water field with water depth of 4500 ft, under a 6000 ft thick salt body, about 190 miles south of New Orleans. BP has the majority of the working interest, (60.5%). The reminder is divided between BHP (23.9%) and Chevron (15.6%)
This successful drilling can be in part attributed to the recent advances in geophysical technologies. The geologically challenging nature of Mad Dog field with about 6000 ft of salt body on top of it, makes it very difficult to correctly map the structure with its detailed fault mechanism. Advances in both seismic acquisition technologies, such as wide azimuth and dual azimuth surveys, and seismic data processing techniques, such as “pre-stack depth migration” methods have been instrumental in many recent successful exploration and field development efforts (e.g. Gulf of Mexico, West Africa and Offshore Brazil.)
Mad Dog structure lies within the western part of the Atwater fold belt, which is a series of Miocene-Pliocene anticlines trending NE–SW. The field lies under a salt canopy with variable thickness of up to 8000 ft. Water depths over the field vary from 4100 ft to more than 6000 ft and vary most quickly along the Sigsbee Escarpment. The total depth of the target is about 22,200 ft. Its discovery was based on a 1996 vintage 3D speculative data shot by Western (now part of Schlumberger). After the discovery, a proprietary 3D survey was shot by Geco (now part of Schlumberger).
In 2004, Industry's first large scale wide-azimuth towed-streamer survey (WATS) was shot to help in better development of the field. This survey, acquired by CGGVeritas, involved a 4-kilometers (km) crossline offset and a 250-m shot line spacing. They deployed eight cables separated by 125 meters, which required them to cover the area four times to obtain the desired 4 km of crossline coverage. The two source vessels each had two air-gun arrays, and each array fired every 37.5 meters.
BP has shown that WATS helped to significantly improve the subsurface image quality in Mad Dog field. One such example is the April 2007 article in the Leading Edge of Geophysics, published by the Society of Exploration geophysicists. They reported the successful development and testing of their marine WATS survey tailored to the needs of Mad Dog. The new WATS geometry yielded improved sub-salt images compared to the conventional “narrow-azimuth” and dual-azimuth images. Additionally, the WATS geometry allowed them to further refine the subsurface velocity model to yield further improvements. The WATS data allowed refining the velocity model by producing a higher resolution sediment velocity field. The new seismic data had fewer artifacts within the salt, and illumination of the salt is better, allowing for a less ambiguous interpretation of salt interfaces and the fault blocks.
Use of advanced geophysical technology will undoubtedly lead to further success in Mad Dog and other sub-salt plays in the Gulf of Mexico and elsewhere. “With these additional hydrocarbon resources in the west and south of the field, Mad Dog has been firmly established as the third giant field in BP’s Gulf of Mexico portfolio, joining Thunder Horse and Atlantis,” said Andy Inglis, BP chief executive officer, exploration and production. BP is currently reviewing development options to increase production from Mad Dog either through debottlenecking the existing facility or by adding another production facility, the company said. BP is the largest producer of oil and gas in the Gulf of Mexico with net production of over 400 mboed. Aside from the above mentioned Mad Dog, 2005, Atlantis, 2007, Thunder Horse 2008, other major BP developments in the deepwater Gulf of Mexico include: Pompano, 1994; Marlin, 2000; Horn Mountain, 2002; Na Kika, 2003; and Holstein, 2004.
Fred Aminzadeh consults with leading institutions through GLG
Analyses are solely the work of the authors and have not been edited or endorsed by GLG.
