Disclosed on page 76 of BHP's annual report, released in September, but also revealed by the recent final investment decision announcement on the $US6 billion ($A7 billion) Gulf of Mexico petroleum project, Deutsche analysts said they were surprised BHP walked away from its 20% or $450 million stake in Stampede.

They also took stock of BHP's plans to sell its Fayetteville shale gas assets in their resulting commentary.

"The decision to walk away from Stampede and also put the 25%-plus IRR [internal rate of return] Fayetteville field up for sale appears to be based on the drive to reduce group capex, with value now being sacrificed to maximise free cash flow," the analysts said according to the Australian Financial Review.

BHP has recently told Bloomberg that the Stampede divestment was made as the company focused on the higher-return opportunities within its portfolio.

The Stampede project is targeting capacity of 80,000 barrels per day through a tie-back of subsea infrastructure to a newly built tension leg platform with first production targeted for 2018.

Chevron, Hess Corporation, Statoil and Nexen each have a 25% stake in this project that will develop the Knotty Head and Pony discoveries, with all of these parties snapping up 5% of BHP's former share each.