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Deepwater Discoveries Build GOM Inventory

One day after Chevron Corp. announced a discovery at the Moccasin prospect in the deepwater Gulf of Mexico (GOM), BP plc said last Wednesday it has drilled a successful appraisal well in an untested segment of the massive Mad Dog field, which may double the size of its entire field's potential resources.

The newest well was drilled in the northern part of the Mad Dog field in Green Canyon Block 738, about 140 miles south of Grand Isle, LA, in 4,500 feet of water. According to BP, the well encountered about 166 net feet of hydrocarbons in the Miocene sands and discovered an oil column of more than 300 feet. Combined with successful appraisals of Mad Dog South in 2009 and pending further testing, BP estimates that the Mad Dog field may hold up to 4 billion boe.

"With these additional hydrocarbon resources north of the main field, Mad Dog has been firmly established as a giant field in BP's Gulf of Mexico portfolio, rivaling Thunder Horse in size of resource," said CEO Bob Dudley.

BP's Thunder Horse facility in the GOM currently is the largest deepwater production unit in the world with capacity to process up to 200 MMcf/d of gas and 250,000 b/d of oil.

The northern Mad Dog appraisal well was drilled by BHP Billiton, 23.9% stakeholder, on behalf of BP, which is the unit operator with a 60.5% interest. Chevron holds a 15.6% stake in the field. BHP operates the southern Mad Dog field. After a successful appraisal well was completed in a southern portion of the field in 2009, BP, which is the biggest operator in the GOM, said then Mad Dog was one of the largest in its GOM portfolio (see NGI, July 20, 2009).

Mad Dog, first discovered in 1998, was the second of four large offshore fields discovered by BP during the 1990s; production ramped up in early 2005 (see NGI, Jan. 24, 2005). As many as 150 drilling and production personnel operate the truss spar platform, which is designed to drill and produce from at least 12 wells simultaneously (see NGI, Aug. 4, 2008).

The truss spar platform at the Mad Dog field originally was designed to process 60,000 MMcf/d of gas and up to 100,000 b/d of oil. In 2009 resource recovery estimates led BP to plan another spar production facility to the field with a capacity of 120,000-140,000 boe/d. Oil and gas are transported from current Mad Dog fields to existing shelf and onshore interconnections via the Mardi Gras Transportation System, which BP operates.

"Coupled with the recent exploration success at the discovery at the Moccasin prospect, located in Keathley Canyon, the Mad Dog result reemphasizes the exploration and development potential of the Gulf of Mexico and the region's ability to continue to deliver material projects for BP," said Dudley.

Chevron last Tuesday said it struck oil at its Moccasin prospect in Keathley Canyon Block 736. The Moccasin well, drilled to a depth of 31,545 feet, is about 16 miles off the Louisiana coast in 6,759 feet of water. The Keathley Canyon Block 736 Well No. 1 encountered more than 380 feet of net pay in the Lower Tertiary Wilcox Sands, the oil major said. The well is about 16 miles off the Louisiana coast in 6,759 feet of water and was drilled to a depth of 31,545 feet.

"The Moccasin discovery underscores the importance of the deepwater Gulf of Mexico as a source of domestic energy for the United States and as a focus area for Chevron's worldwide exploration portfolio," said Vice Chairman George Kirkland, who is in charge of Chevron's upstream business. "Moccasin is an important addition to our queue of high-quality opportunities around the globe" (see related story).

Chevron began drilling the Moccasin well in March 2010, but work was halted three months later when the deepwater drilling moratorium was imposed following the Macondo well blowout. Drilling resumed in March after the Bureau of Ocean Energy Management, Regulation and Enforcement approved Chevron's revised drilling permit application (see NGI, March 28).

Well results from the Moccasin well still are being evaluated, and additional work will be needed to determine the extent of the resource, said Chevron. The company holds a 43.75% working interest in Moccasin and operated the discovery well. Other well owners are BP (43.75%) and Samson Offshore Co. (12.5%).

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