Production from the 12-year-old discovery has required a U.S./Mexico agreement on to whom the oil belongs.

Resolution pending in Washington of oilfield-development law along the Perdido Foldbelt in the Gulf of Mexico would make production from Chevron Corp.’s tremendous, 12-year-old Trident discovery and several others possible.

The oil reserves in the Trident area, some 185 miles southeast of Corpus Christi and four miles from Mexico’s maritime border, were established by explorers on the U.S. side of the marine boundary but exist under both the U.S. and Mexico seabeds.

Legislation the U.S. House passed in late June would resolve how profits from oil and gas produced from these fields would be shared with Mexico and, if Mexico’s state-owned Pemex were to produce from the Perdido Foldbelt as well, then vice versa.

The legislation requires Senate support and President Obama’s signature. Impeding progress, however, is that the House version of the legislation includes a controversial exemption to the Frank-Dodd Act of 2010 that requires, for example, that U.S. companies disclose royalty payments made to foreign governments.

In 2001, Unocal Corp., which had a string of tremendous deepwater Gulf of Mexico failures in the late 1990s, announced its Trident success in July 2001 in Alaminos Canyon Block 903. A $34-million wildcat, it encountered more than 300 feet of 40-degree-plus oil pay and other possible payzones beneath 9,687 feet of water at a total depth of 20,500 feet.

A Unocal vice president said of the discovery at the time that the size of the structure Unocal tested had “up to 10,000 acres in structural closure.”

The Trident discovery involves seven Alaminos Canyon blocks.

Partners in 2001 were Chevron, which bought Unocal in 2005 and now owns Unocal’s interest in Trident as well; Italy-based Eni SpA; Phillips Petroleum Inc., which is now owned by ConocoPhillips; and Ocean Energy Inc., which was bought by Devon Energy Corp. in 2003. In 2010, Devon sold its entire deepwater Gulf portfolio to BP Plc.

Additional Gulf frontier discoveries in the Perdido Foldbelt are Great White, Baha and Tobago, according to Javier Estrada, a former commissioner of Mexico’s Energy Regulatory Commission.

“The drilling and discovery of hydrocarbons during 2001 at the Trident 1 wildcat proved the exploration viability of the Perdido Foldbelt in the Alaminos Canyon,” Estrada explained in a joint meeting of the U.S. and international associations for energy economics (USAEE, IAEE) in 2007.

“It is an area characterized by water depths reaching more than 10,000 feet, difficult drilling conditions and risk of damages caused by hurricanes. Industry reports inform that the geologic insights gained so far include the discovery of high-quality light oil, the recognition of multiple hydrocarbon source rocks, the age of key seismic markers, and the presence of abundant and well-developed sandstone reservoirs.”

It is estimated that Mexico owns 80% of these structures, he added.

Editor’s Note: For more on Trident and other ultra-deepwater Gulf of Mexico discoveries see the cover stories, Oil and Gas Investor, Deepwater Gulf, May 2002, and Foldbelt Fever, October 2004.

-Nissa Darbonne, Editor-at-Large, Oil and Gas Investor, OilandGasInvestor.com, Oil and Gas Investor This Week, A&D Watch, A-Dcenter.com, UGcenter.com. Contact Nissa at ndarbonne@hartenergy.com.