?A shale that’s enjoying a shot in the arm is the Cretaceous Baxter in the Greater Green River Basin. Oklahoma City-based Devon Energy Corp., a shale heavyweight, has made a couple of deals in this emerging play, located in Moffat County, Colorado, and Sweetwater County, Wyoming.

Australian firm Samson Oil & Gas, which has offices in Denver, has announced an agreement with Devon. The latter will farm into 6,400 acres held by Samson in Sweetwater County. Here, the Cretaceous Baxter shale attains 3,500 feet in thickness, and is found at depths of 10,000 feet. Gas has flowed at intriguing rates in old wells. A particular zone of interest within the Baxter is the thin, but areally extensive, Airport sandstone.

This summer, Devon plans to acquire 3-D seismic on the Samson acreage block, which sits in the midst of a large Devon position. Going forward, Samson will retain a 50% interest in the lease block; Devon will have the balance and assume operations.

Some 40 miles east of Samson’s acreage, Salt Lake City-based Questar Corp. and Denver independent Kodiak Oil & Gas Corp. have been working on Baxter shale in the Vermillion area in northwestern Colorado in a sub-basin of the Greater Green River.

Devon has also entered this side of the Baxter play. Earlier this year, it farmed into 10,334 acres of Kodiak leases and pledged to drill three Baxter tests on that acreage. Kodiak will be carried on the wells and will retain a 50% working interest.

The entry of an experienced, deep-pocketed shale operator such as Devon is positive news for the Baxter. Initial drilling results have been spotty, and the work in the Vermillion portion of the play has been plagued by high well costs and lower-than-hoped-for recoveries.

Excitement was tangible in early 2007, when Questar’s #13C Trail, a vertical well, was tied into sales at rates of 9 million cubic feet a day. That was several times greater than antecedent wells, and seemed to indicate that natural fractures were crucial to good production.

Subsequent attempts to drill horizontal wells were disappointing, however. The wells either experienced mechanical problems or production dropped off quickly. Clearly, the Baxter is a case of a huge resource that needs some engineering breakthroughs.

"We think the Baxter is not like the Barnett shale,” says Terry Barr, Samson president and managing director. “The Baxter is more of a source rock that is naturally fractured, and it will produce free gas from those fractures rather than adsorbed gas.”

Some conclusions that Barr has drawn from Questar’s work in the Baxter are that overpressuring, the use of 3-D seismic to locate natural fracture systems, and the use of horizontal drilling in the Airport sandstone lens are all important.

Indications are that each of these factors can be brought to bear in Samson’s area of interest.

Some evidence can be gleaned from 3-D seismic data. In Samson’s slice of Sweetwater County, move-out velocity techniques indicate that the top of the Baxter appears to be overpressured; this is confirmed by well data.

The 3-D can also be combed to find areas of fracturing. Two geophysical techniques are promising for fracture detection. Semblance compares traces with their neighbors, and lack of semblance indicates fracturing.

Differential velocity is another technique. Minimum and maximum interval velocities at the Airport sandstone are compared, and situations where they fail to coincide are thought to pinpoint fractures.

Additionally, regional well control indicates the Airport sandstone, which acts both as a storage system and a conduit for gas, is developed.

After the new 3-D data is acquired, it will be time to drill wells. Barr expects horizontal Baxter wells in Samson’s area will cost around $5 million.

“We know that the Baxter is structurally incompetent, and the jury is still out on the best way to drill and complete the horizontal wells. We’re excited about Devon’s interest in the play, and the experience it brings to the Baxter,” he says.

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