Delaware basin shales strain for economics

The Mississippian Barnett shale has the potential to be a prolific gas producer in the Delaware basin, write geoscientists in the AAPG Bulletin.

By OGJ editors
HOUSTON, Sept. 3 -- The Mississippian Barnett shale has the potential to be a prolific gas producer in the Delaware basin, write geoscientists in the AAPG Bulletin.

One well is reported to have an estimated ultimate recovery of 9 bcf, said Travis J. Kinley of Texas Christian University and fellow authors. Drilling and stimulation costs to as deep as 18,000 ft began at more than $18 million and have been reduced to about $8 million.

Interval A at the top of the Lower Barnett typically has resistivities of 50-100 ohm-m and "is believed to be a significant zone of gas saturation within the Barnett," they reported.

For the most part, however, shale gas plays in the basin have resisted efforts for viable economic development.

Both the Barnett and Devonian Woodford shales should be evaluated, but silica content is less than in the Fort Worth basin. Shale is brittle and will not fracture as well, and proppant embedment may be a problem, the authors wrote.

Shales can slough in horizontal wells, and the high pressures challenge frac pumping equipment.

Even so, a few wells have made initial flow rates of up to 3 MMcfd, and IP at the best well was 5 MMcfd, but decline rates are steep. Chesapeake Energy Corp. and Hallwood Energy Corp. have commercial gas sales.

Using logs from 150 wells in a study area of 500 sq miles in the northern part of the basin in West Texas and Southeast New Mexico, Kinley el al. said that areas for future exploration focus can be delineated by mapping a net resistivity greater than 50 ohm-m. No core was available, but the group studied mud logs and cuttings from five wells.

They noted that the first Delaware basin shale gas wells were drilled in southwestern Reeves County in 2002, and shale gas activity in West Texas has waxed and waned over the last 5 years.

They also noted that it took years to discover the correct combination of drilling and completion techniques to tap gas in the Barnett shale in the Fort Worth basin.

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