AAPG: Contrary thought led to great finds

Unconventional geologic thinking and risk-taking led to many of the world’s recent major oil and gas discoveries, speakers from the companies that made them told a closing session at the American Association of Petroleum Geologists annual convention in Denver.

Alan Petzet
Chief Editor-Exploration

DENVER, June 12 -- Unconventional geologic thinking and risk-taking led to many of the world’s recent major oil and gas discoveries, speakers from the companies that made them told a closing session at the American Association of Petroleum Geologists annual convention in Denver.

Hardly anyone was interested in Ghana’s offshore when Kosmos Energy Inc., Dallas, decided to explore its deepwater transform margin in 2003, said Phil Lowry, Kosmos senior reservoir geologist.

The Tano basin had three small Albian oil fields and two Late Cretaceous oil fields in shallow water, but earlier explorers felt the deepwater parts of the margin were too risky, Lowry said. Kosmos Energy raised $300 million in 2004 to explore the area.

After imagining an Upper Cretaceous source instead of or in addition to the established Albian source, the company shot 1,000 sq km of 3D seismic in 2005 and perceived potential in stratigraphic pinchout and combination structural traps.

With Anadarko Petroleum Corp. and Tullow Oil PLC as partners, the 2007 Mahogany-1 discovery well in 4,330 ft of water found more than 300 ft of net pay in Cretaceous sandstone and had estimated deliverability of 16,750 b/d.

First production from the discovery, named Jubilee, is expected in 2010. The first development phase is to tap 300 million bbl of oil and reach a production peak of up to 120,000 b/d.

Strong out of the box thinking and aggressive management backing led Chesapeake Energy Corp., Oklahoma City, to investigate and pursue gas in the Jurassic Haynesville shale in Louisiana and Texas, said Chesapeake’s John L. Sharp.

Chesapeake drilled the play’s first horizontal well in June 2007 in Caddo Parish, La. Now the industry is producing an estimated 400-450 MMcfd from the calcareous mudstone and pursuing it with about 90 rigs, Sharp said. Haynesville production will grow to 2-2.5 bcfd by the end of 2011, he estimated.

Overpressuring at .85-.87 psi/ft of depth is the main reason the Haynesville is destined to become the largest gas field in the US and fifth largest in the world, Sharp said.

“The 20-28 MMcfd wells are real,” he said.

North Caspian Operating Co., successor to Agip KCO, is the new operator of supergiant Kashagan oil and gas field in the Caspian Sea off Kazakhstan, said William Zempolich of Eni SPA.

NCO’s operating group completed the Kashagan East, West, and Southwest, Kairan, Aktobe, and Kalamkas discovery wells in Paleozoic carbonates below thick and variable Permian salt in the North Caspian basin.

Kashagan field, discovered in 2000, is a Devonian and mid-Carboniferous structure 35 km long at 4,000 m deep with 45° gravity oil and a GOR of 2,800-3,000 scf/bbl in 2-4 m of water. It is overpressured and high in hydrogen sulfide. It was discovered based on 1,475 sq km of ocean-bottom seismic shot in 2001-02.

Production islands will have barriers to protect central islands from ice.

Half of the produced gas will be reinjected, and the other half will go to gas processing plants at the Boleshak onshore production facility.

Large deepwater subsalt discoveries in the Gulf of Mexico Lower Tertiary Trend have the potential to return gulf oil production to the 4 million b/d peak formerly attained solely from shelf fields, said James Cearley of Chevron Corp.

Among the operating challenges are multistage salt canopies below which explorers can encounter the Wilcox three times and loop currents that can deflect risers so far that rotating drillpipe can burn a hole in them, Cearley noted.

Cumulative production of 500,000 bbl/well equates to a recovery factor of less than 2% in North Dakota’s Bakken formation, said Mark Williams, Whiting Petroleum Corp., Denver.

Many wells average 10,000 ft of true vertical depth and a 10,000-ft lateral with 10 sliding sleeves for frac stages, and Whiting has drilled two laterals that extend across 2 sq miles each. These 1,280-acre units have room for a second and possibly a third 2-mile lateral, Williams said.

He said the Bakken play has more than 700 horizontal wells, most of them drilled since 2004 and heavily weighted to 2007-09, and that wells for which operators have reported initial production of 1,000 boe/d or more have almost exclusively been in the Parshall/Sanish field area.

Contact Alan Petzet at alanp@ogjonline.com.

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