| Coal reservoir quality in the Ferron Sandstone Member of the Mancos Shale, and in the Fruitland Formation is dependent on coal cleat characteristics. Coal reservoir permeability increases as a result of high cleat density. From careful outcrop examination, we were able to identify several factors that increase cleat density. Vitrain coal typically has the highest fracture density as a result of having well-developed face cleats and conchoidal fractures. Clarain coal contains face and butt cleats. Cleat density in clarain is also controlled by mechanical layer thickness. As mechanical layer thickness decreases, cleat density increases. Durain and fusain coals typically contain no well-developed cleat system, although their presence can affect mechanical layer thickness in adjacent coals, as they may form bounding units. Cleat density increases in the damage zone of faults and in the hinge-line of folds. Cleat-controlled reservoir permeability has beneficially affected methane production in one portion of the Drunkards Wash Gas Field, Utah, and appears to have negatively influenced methane production in the coalbed methane field. |
