Characterization of Coal-Bed Methane Reservoirs, Ignacio- Blanco Fruitland Field, LaPlata County, Colorado

W. C. Riese and Walter W. Ring

Coal reservoirs in the Ignacio-Blanco Fruitland Field, LaPlata County, Colorado have been exploited for methane production for several years. Enough performance history has accumulated to confirm that various completion and stimulation techniques impact production rates differently across the field. These data also imply that the character of the coal itself varies across the field, so completion techniques which are effective in one part of the field may not be effective in another.

Petrologic study of the coal available in three cores was undertaken to determine the nature of changes in coal character and properties across the field, and to identify and recommend alternative stimulation and treatment procedures. This study employed a broad spectrum of analytical techniques including electron microprobe and CT scanning and imaging techniques, as well as more conventional mineralogical, organic content, and chemical and isotopic analyses.

These analyses indicate that the gross ash content does not vary systematically across the field and that the ash content did not seem to influence cleat formation in the coals. Mineralogy of the ash found kaolinite to be the dominant clay in some portions of the field and montmorillonite and illite to be dominant in others; pyrite was present in the areas dominated by smectites. CT image analysis found that both cleat formation and character varied across the field; it also found that microporosity is locally quite pervasive.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California