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Unocal on to Tobago Alaminos Canyon prospect may provide key to ultra-deepwater development Ray Tyson Petroleum News Houston Correspondent
Unocal, following announced dry holes at Myrtle Beach and House Payment in the Gulf of Mexico, has turned its full attention to a potentially key prospect in the ultra-deep waters of the Western Gulf called Tobago.
Located on Alaminos Canyon Block 859 between Unocal’s Trident and Shell’s Great White discoveries, Tobago could provide the necessary additional reserves to justify field development and investment in a “hub” or central facility to handle production from various fields.
Trident contains an estimated 150 to 200 million barrels of oil equivalent. And though Shell has never disclosed Great White reserves, analysts speculated it could hold some 400 million barrels of equivalent. In shallower waters of the Gulf, where pipelines and other infrastructure already exist, fields the size of Trident and Great White likely would be developed swiftly and independently.
But in 10,000 feet of water and scores of miles from any conventional crude transportation system, the southern reaches of Alaminos Canyon promise to be an expensive place to do business. Field owners have explored several options for Trident and Great White, including a floating production, storage and offloading facility, which is typically used for isolated fields around the globe but has yet to make its debut in the Gulf. Marine tankers are used to transport oil from the FPSO to shore, eliminating the need for an expensive pipeline system.
Unocal has provided little information about its Tobago prospect, saying March 26 only that it plans “to test a structure” between Trident and Great White using the drillship Discoverer Spirit. Unocal had high hopes for Myrtle Beach In regard to its Myrtle Beach well on Green Canyon Block 943 and its House Payment well on Eugene Island Block 40, which “did not encounter commercial quantities of hydrocarbons,” Unocal said it would charge the costs of the exploratory wells in the 2004 first quarter.
Unocal had high regard for Myrtle Beach following an impressive hit at its Puma prospect in southeastern Green Canyon, which has spawned numerous discoveries in the past. Unocal noted then that the Puma-1 exploratory well confirmed the area’s prolific lower and middle Miocene sands and “further enhances prospectivity” of the region, where Unocal had begun drilling the Myrtle Beach well.
Unocal operated the Myrtle Beach well with a 25.6 percent working interest. Partners included ExxonMobil with 27.8 percent, Amerada Hess with 20 percent, Pioneer Natural Resources with 10 percent interest, Maxus (U.S.) Exploration Co. with 10 percent, and an unidentified “co-venturer” with a 6.6 percent interest. At House Payment, Unocal was operator and held a 50.2 percent working interest, followed by The Houston Exploration Co. with 33.3 percent, and Devon Energy with 16.5 percent. Unocal will also drill at St. Malo In addition to Tobago in Alaminos Canyon, Unocal’s deepwater Gulf of Mexico drilling plan for 2004 includes an appraisal well at the St. Malo discovery on Walker Ridge Block 678 and Sardinia, a lower Tertiary test on Keathley Canyon block 681.
Industry analysts are keeping a close watch on St. Malo. The discovery well is said to have encountered more than 450 feet of net oil pay over a gross hydrocarbon column of 1,400 feet, indicating a major hydrocarbon accumulation by Gulf standards.
Both the net pay and gross hydrocarbon column encountered by the St. Malo discovery well are comparable to those found at such deepwater Gulf finds as Tahiti, Atlantis, Mad Dog, Neptune and Cascade. Tahiti alone contains estimated reserves of 400 to 500 million barrels of oil equivalent.
St. Malo also is in the same area of Walker Ridge and is a similar play concept to Unocal’s 2002 Cascade discovery, which is thought to contain more than 300 million barrels of oil equivalent. Cascade also is said to be important because it penetrated the deep Eocene section, where it encountered a hydrocarbon column that one of the partners characterized as a “potentially significant” discovery.
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