RS-33 Spanish Peak Field, Las Animas County, Colorado: Geologic Setting and Early Development of a Coalbed Methane Reservoir in the Central Raton Basin


Opportunities exist to develop Vermejo coalbed methane reserves within the Trinidad Sandstone outcrop area from the New Mexico state line to the northern side of Cucharas River drainage. This report discusses the geology and hydrology of the Spanish Peak Field, as well as coalbed methane development. Includes a summary and references. 34 pages. 21 figures. 2 tables. Digital PDF download. RS-33D

From the Abstract:

The Raton Basin’s Spanish Peak coal bed methane (CBM) field was discovered in 1993 by Evergreen Resources, Inc., Denver, Colorado, which drilled and completed a cluster of four exploratory wells located 7 to 8 mi northwest of the small town of Tijeras, Colorado. In January 1995 Evergreen placed three of the wildcats and six additional 1994 field development wells on line. Nearly 4.1 billion cu ft (BCF) of CBM was produced from 45 wells through 1996. In the fall of 1996 Evergreen accelerated its field development program. (December 1996 field production volume averaged 12.9 million cu ft (MMCF) of gas per day: March 1997 deliveries exceeded 17 MMCF from 53 active wells). In early March 1997, Evergreen announced plans to drill and complete an additional 40 CBM wells in the Raton Basin during 1997. It is believed that 36 of these wells will be located in the Spanish Peak development area.

The primary source of Spanish Peak field production is coal beds in the Vermejo Formation (Late Maastrichtian). A very small proportion of the field gas is contributed by coals in the overlying Raton Formation (latest Maastrichtian — early Paleocene). The base of the Vermejo Formation and the top of the conformably underlying Trinidad Sandstone in the Spanish Peak field area varies from about 750 to 1,800 ft below ground surface. Part of this range is related to the region’s basin structure, but more than half reflects topography dissected by the Purgatoire River and its tributaries. The thickness of the Vermejo Formation in the Spanish Peak field area varies from 350 ft to 225ft. The average thickness of the Vermejo Formation in the field area is 290 ft. Individual coal seams in the Vermejo Formation range from several inches to more than 14 ft thick, total aggregate coal thickness in the Spanish Peak field area ranges from 19 to 44 ft.

Evergreen drills field wells in about one day using an air percussion rotary rig (somewhat like a jackhammer). After reaching total depth of about 200 ft below the base of the Vermejo Formation in the upper Pierre Shale, Evergreen sets 5.5-in. casing on bottom with cement set through the coal reservoir sequence. Individual wells are completed to produce gas from five to fifteen individual coal seams. The coal zones that are opened with perforations are fracture-stimulated in two or three stages, using on the average 75,000 to 100,000 pounds of sand per stage and from 300 to 400 bbl of water mixed with nitrogen as a carrying agent. An occasional well is completed in four stages. The present field spacing is 160 acres per well.

This study of Spanish Peak field in an early stage of development and productive life is significant because it: (1) demonstrates that commercial levels of CBM have been attained in the central Raton Basin area, (2) provides substantial incentive to explore for additional CBM fields along and east of the Raton Basin synclinal axis from Spanish Peak north into the Cucharas River drainage, and (3) suggests a rather simple strategy for locating fairways of enhanced coalbed permeability in the Central Raton development area and northern Raton exploration area. The strategy is based on synthesis of Spanish Peak geologic and reservoir performance data.