Petrologic Factors Controlling Coal Gas Contents of Fruitland Formation Coals, San Juan Basin, New Mexico

MOORE, THOMAS R., Phillips Petroleum Company, Farmington, NM, and DANIEL L. PEARSON and DAN C. BOATWRIGHT, Phillips Petroleum Company, Bartlesville, OK

The petrologic factors controlling coal-bed gas content in coals of the Fruitland Formation in the central San Juan basin are abstruse, with many of the factors being complexly interrelated. Data for this study were derived from 78 samples collected from seven cored wells in Rio Arriba and San Juan counties, New Mexico, and include desorption gas content, proximate analyses, maceral modal analyses, vitrinite reflectance, x-ray diffraction mineralogy, and pyrolysis values. Although several of the measured parameters affect gas content in a general sense, no single petrologic factor is strongly correlated to desorbed gas content.

Principal component analysis was used to group the measured parameters into associations of related variables. The first principal component, accounting for 34% of the total variation in the data set, is dominated by parameters that vary strongly with organic matter maturity, namely vitrinite reflectance (Ro), volatile matter and fixed carbon contents, hydrogen index, and pyrolysis-generated thermally extractable hydrocarbons (S2). Ash content and other measured parameters correlatable to it account for 19% of the total variation as the second principal component. The third principal component (13%) is controlled by variation in the maceral content and the fourth principal component (8%) is primarily comprised of thermally extractable hydrocarbons (TEH or S1), hydrogen index, and as-r ceived moisture content. Reification and interpretation of the principal component analysis are dependent upon an understanding of the Fruitland depositional system, the burial diagenesis of the coal-bearing strata, and coal-bed gas desorption phenomena.

AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)