Talk Title: Atlantic Rim Coalbed Methane Play: The Newest Successful CBM Play in the Rockies
Speakers: Robert A. Lamarre, Lamarre Geological Enterprises, LLC, and Stephen K. Ruhl, Anadarko Petroleum Corporation
Date: February 4, 2005
Publication: The Outcrop, February 2005, p. 4-5
The Atlantic Rim Coalbed Methane Play is rapidly becoming one of the most significant new CBM discoveries in the Rockies. The play is on the shallow eastern margin of the Washakie Basin, in Carbon County, Wyoming. The play area is 55 miles long by 5 miles wide, targeting prospective coals in the Almond and Allen Ridge formations of the Mesaverde Group. The explorat0ry fairway is narrow because the coals are present in outcrop on the eastern side of the play, and on the western side the drill depths exceed 5,000 feet as the coals dip three to six degrees to the west into the deep Washakie Basin.
Eighty-one wells have been drilled in the play and 41 wells produced 9,689 Mcfpd and 45,273 Bwpd from Almond and Allen Ridge coals during July 2004. Thirty-two new wells were drilled during 2004, and they are waiting on completion and/or hook-up to the gas pipeline.
Data from wells within four different productive areas indicate that the relatively low rank coals (high volatile C bituminous) contain 175 to 350 scf/ton gas on a dry, ash-free basis. The total coal thickness ranges from 40 to 80 feet at depths of 200 to 3,000 feet. Adsorption isotherms indicate that most of the coals are fully saturated. Water quality within the coals ranges from 1,000-1 ,450 ppm total dissolved solids. Potential reserves in coals of both formations may be as high as 3.0 Bcf per well, based on 160-acre spacing.
We suspect that the play contains thermogenic and biogenic gas in a combination structural/stratigraphic trap, with the gas being held in place by down dip flow of meteoric water from the high Sierra Madres to the east. This influx of fresh water has probably contributed biogenic gas to the coal reservoirs, resulting in higher than expected gas contents. The first CBM production in the play was from a four-way closure at Cow Creek Field. Additional drilling to the east has established commercial production from a structural nose at the Sundog Pod. Recent drilling in areas with only regional dip has established very good permeability, and some wells are beginning to make a significant amount of gas. Coals and carbonaceous shales that are deeply buried near the center of the Washakie Basin are generating thermogenic gas today. Some of this gas has probably migrated up dip to the east to help form the large coalbed methane occurrence that is currently being exploited.