Shell has boosted the economics for its next likely major hub development in the US Gulf of Mexico, with a 100 MMboe ultra-deepwater discovery at Rydberg in its prolific Norphlet play.

This is the latest find in the Norphlet trend in the eastern Gulf, which was first targeted by Shell more than a decade ago and which has so far unearthed two large rewards at Appomattox A (in 2010) and Vicksburg (in 2013). The Rydberg discovery takes the total recoverable resources estimate up to approximately 700 MMboe, with the latest find located 16 km (10 miles) from Appomattox.

Well-placed industry sources point to a 2019 onstream date for Appomattox, located in Mississippi Canyon Block 392 and for which a FEED phase is already underway. Up to 500 MMboe of recoverable reserves have so far been estimated for Appomattox.

Shell is understood to be studying a semisubmersible floater for Appomattox, with a production capacity of more than 100,000 boe/d, making it larger than the same operator’s previous Nakika deepwater platform in the GoM.

Houston Offshore Engineering (HOE) is performing the topsides FEED for Appomattox, while IntecSea is undertaking another on the hull, DI hears.

Samsung, meanwhile, is understood to have a letter of intent in place for fabrication of the hull, while Kiewit has another LoI from Shell for the topsides and platform integration.

The deepwater Vicksburg discovery, five miles from Appomattox, is still undergoing appraisal work, and will follow Appomattox into production, probably via a subsea tieback, with Rydberg to follow on after as capacity becomes available.

A Shell Oil spokeswoman told DI: “The Appomattox project, now in the define phase, is moving ahead with engineering design for the floating production system, subsea infrastructure and wells. Please note that the Appomattox project is pre-sanction.”

Kiewit has neither confirmed nor denied an LoI for Appomattox, and referred an inquiry about it back to Shell.

Shell confirmed Rydberg as a discovery in MC 525 in 2,280?m (7,479 ft) of water after it was drilled to a total depth of 8,038 m (26,371 ft) by the Noble Globetrotter I drillship. The well encountered up to 122 m (400 ft) of net oil pay, located 120 km (75?miles) offshore.

The drillship is now being moved again to target another deepwater prospect, Gettysburg in Desoto Canyon Block 398. Well results from Rydberg are still being evaluated but the expectations are that the resources in the discovery will be approximately 100 MMboe. Shell added that, with Appomattox and Vicksburg, “...this brings the total potential Norphlet discoveries to over 700 MMboe”.

Rydberg represents a long haul of 13 years exploration for Shell after company geologists first targeted the Jurassic play back in 2001, starting with the theory that it extended into the offshore from onshore, and acquired the first lease in the region the same year. Typically Shell says the play type features high pressure/high temperature reservoirs. Non-commercial discoveries by Shell in the Norphlet trend include Shiloh (2003) and the 2009 Antietam discovery.

Discussing the commercial finds, Marvin Odum, Shell’s Upstream Americas Director, said these successes represented the emergence of another hub for the company’s deepwater activities. Because of its proximity to other discoveries, he added, Rydberg was “...particularly exciting”.

Shell operates Rydberg with 57.2%, Ecopetrol America holds 28.5% and Nexen 14.3%. Vicksburg is operated by Shell with 75%, with Nexen holding 25%, while on Appomattox operator Shell has 80% and Nexen 20%.

Offshore