Organic petrology and coalbed gas content, Wilcox Group (Paleocene–Eocene), northern Louisiana

• Published in: International journal of coal geology Vol. 71; no. 1; pp. 54 - 71
• Main Authors: Hackley, Paul C., Warwick, Peter D., Breland, F. Clayton
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.2007; Elsevier
• Subjects: Coal; Coalbed methane; Earth sciences; Earth, ocean, space; Exact sciences and technology; Louisiana; Organic petrology; Wilcox Group; Louisiana; North Atlantic; Gulf of Mexico; United States; Northwest Atlantic; North American Atlantic; Louisiana; Wilcox Group; Coal; Organic petrology; Coalbed methane; coalbed methane; Paleogene; springs; Atlantic Ocean; Paleocene; precursors; exhibits; North America; rank; lignite; Cenozoic; peat; deltas; clastic rocks; gas storage; shale; carbonaceous rocks; adsorption; soil moisture; Tertiary; Eocene; isotherms; sedimentary rocks; materials; coal; programs; Phanerozoic; desorption; macerals; progradation
• ISSN: 0166-5162; 1872-7840
• DOI: 10.1016/j.coal.2006.05.009

Wilcox Group (Paleocene–Eocene) coal and carbonaceous shale samples collected from four coalbed methane test wells in northern Louisiana were characterized through an integrated analytical program. Organic petrographic analyses, gas desorption and adsorption isotherm measurements, and proximate–ultimate analyses were conducted to provide insight into conditions of peat deposition and the relationships between coal composition, rank, and coalbed gas storage characteristics. The results of petrographic analyses indicate that woody precursor materials were more abundant in stratigraphically higher coal zones in one of the CBM wells, consistent with progradation of a deltaic depositional system (Holly Springs delta complex) into the Gulf of Mexico during the Paleocene–Eocene. Comparison of petrographic analyses with gas desorption measurements suggests that there is not a direct relationship between coal type (sensu maceral composition) and coalbed gas storage. Moisture, as a function of coal rank (lignite–subbituminous A), exhibits an inverse relationship with measured gas content. This result may be due to higher moisture content competing for adsorption space with coalbed gas in shallower, lower rank samples. Shallower (< 600 m) coal samples consistently are undersaturated with respect to CH 4 adsorption isotherms; deeper (> 600 m) coal samples containing less moisture range from under- to oversaturated with respect to their CH 4 adsorption capacity.