Status of Wilcox Coal Seam Natural Gas Play
in Northeast Louisiana
Deane C. Foss
CHC Energy, LLC, 10007 Longmont Dr., Houston, Texas 77042
The Wilcox coal seam natural gas play is located in northeast Louisiana, encompassing Franklin, Catahoula, Richland, Caldwell, Ouachita, LaSalle, Winn, and Grant parishes.
The Riverton Field in Caldwell Parish, operated by Southwestern Energy, is the most successful field to date in the play. There are many issues that determine the degrees of success in this play. Geology is critical, but no more so than cementing, stimulation, and operating equipment, procedures, and supervision. This presentation deals with geological aspects of this play.
Work done to date has defined two coal seam plays in the Wilcox of northeast Louisiana. The first play is the “multiseam” play where the aggregate thickness of several thin coal seams generates a sufficient economically attractive gas-in-place target. The second is the single seam play which focuses on either the Reynolds or the Russell coal seams. Best results to date have come in the single seam Reynolds coal play.
Geologically, the Wilcox is separated into three major parts—Upper (transgressive), Middle (aggradational), and Lower (progradational). Interestingly, the thickest and most isolated coal in the Wilcox in northeast Louisiana—the Reynolds coal—occurs at the top of the progradational sequence. In the most prospective areas of northeast Louisiana it is 15 to 30+ ft (4.6 to 9.1+ m) thick. The Russell coal is associated with the Middle Wilcox aggradational sequence and has greater variability in both thickness and degree of isolation from adjacent water sands.
Gas from Wilcox coal seams has been known for years. Mudlogging units typically recorded “coal gas” or “gas from lignites.” Starting in 2005, companies started measuring the exact gas contents and gas storage capacities in the coal seams. Sufficient gas-in-place triggered pilot development projects and subsequent expansion. Field-wide dewatering began in 2007 at the Riverton and Woolen Lake fields and is ongoing.