The full story of the US Gulf of Mexico discovery that became Stampede dates back to 2005, when Unocal, ultimately acquired by Chevron, made the Knotty Head discovery in Green Canyon Block 512, writes Kathrine Schmidt.

Hess had an adjacent area, Pony, to the north on blocks 468 and 469, and drilled follow-up appraisal wells.

It became clear that the partners had come upon a major accumulation, which today is believed to contain between 300 million and 350 million barrels of oil equivalent.

The reservoir was found in Miocene-aged structures beneath a 15,000-foot thick salt canopy.

Though not high-temperature or high-pressure, the find was especially deep at 30,000 feet. At times there were 17 casing series used.

“The key questions we needed to answer were, how compartmentalised is this reservoir going to be? What is the stratiographic complexity that we’re dealing with? Where are the fluid contacts?” Gerbert Schoonman, Hess vice president for global production offshore, recalls.

Key tools in understanding that reservoir were state-of-the art dual-coil 3D seismic and extensive fault seal analysis, as well as pressure data from wells, core data and logs.

“What we want to do is create an even better image of the reservoir so that once we drill the original phase of Stampede, we can use the well data plus the new seismic data to identify any opportunities for us to develop the reservoir even further,” Schoonman says.

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A Head start for 2005 find