OF-99-10 Correlation of Producing Fruitland Formation Coals Within the Western Outcrop and Coalbed Methane Leakage on the Southern Ute Reservation: Final Technical Report


The CGS and Southern Ute Indian Tribe (SUIT) proposed to determine the cause of several gas seeps which are occurring on the western outcrop of the coalbed methane (CBM) producing Fruitland Formation on the SUIT Reservation. Correlation between outcrop coals and subsurface coals was necessary to determine seep source in the northern part of the study area. Subsurface studies include structure and net coal isopach maps, stratigraphic cross-sections, production maps, and a production database. Detailed coal stratigraphy was correlated through production wells near the outcrop region. These maps and cross-sections were correlated to new surface coal outcrop maps generated by the CGS and the SUIT Division of Energy Resources. Methane gas seepage has been noted historically within the study area. The total investigation may help determine if gas seepage is natural, a result of coalbed methane development, or some combination of the above. Digital ZIP/PDF download. OF-99-10D

From the Executive Sumery:

In the fall of 1997, the CGS supervised the mapping of Fruitland Formation coalbed outcrops on the Southern Ute Indian Reservation. This coalbed methane productive zone crops out along the northern rim of the San Juan Basin as a prominent topographic ridge. Several cross-sections, both strike and dip elongate, were constructed of gas production wells along the outcrop. The logs from wells closest to the outcrop were used in an attempt to correlate productive Fruitland coalbeds to the surface. A geologic map with these coal groups was produced at 1:24,000 scale for the northern half of the study area. The Southern Ute Division of Energy Resources mapped the southern outcrop region in 1996. Coal correlations established from that map were carried through to the northern map. This nomenclature was used to map the coalbeds in the northern part in both surface and subsurface studies. Coals located on outcrop can now be tied to local producing coal intervals. Subsurface data includes a production database, cross-sections, net coal thickness isopach maps, and production index maps. The geologic data can be used for scientific interpretation varying from environmental to coalbed methane production concerns. The maps can enable the user to locate coal outcrops for methane gas seepage, distressed vegetation, and geologic controls of coal production. Correlation of individual coals determined in the subsurface with those mapped in outcrop can help determine whether coal groups contribute to surface seeps known in the area. These correlations may also be used in planning seep mitigation. Monitoring of the Fruitland coal outcrops within the study area can provide important baseline data to future seep studies.