UNDISCOVERED COALBED METHANE RESOURCES OF THE RATON BASIN, COLORADO AND NEW MEXICO

More than 4,325 barrels of oil, 3,864 billion cubic feet (BCF) of gas, and 389 million barrels of water (MMBW) have been produced from the Raton Basin-Sierra Grande Uplift province. Gas production has primarily been carbon dioxide with minor amounts of helium and nitrogen in the Sierra Grande Uplift area. About 286 BCF of coalbed methane (CBM) and 387 MMBW have been produced from more than 1,760 wells in the Raton Basin portion of the province since the start of commercial CBM production in 1984. In 1995, the U.S. Geological Survey estimated mean undiscovered CBM resources at 1.78 trillion cubic feet; the province is currently being reassessed. Production has expanded outside the play boundaries defined in the 1995 assessment, and boundaries in the reassessment include the entire extent of the Upper Cretaceous Vermejo and overlying Cretaceous-Tertiary Raton Formations.

About 90 percent of the CBM gas production is from the Vermejo Formation, with the remainder from the Raton Formation and commingled Raton/Vermejo production. Depths of production range from about 230 to 4,550 ft. Potential gas resources are also located within interbedded sandstones, and from sandstones in the overlying Poison Canyon Formation and underlying Trinidad Sandstone. Total production from the Trinidad Sandstone in the basin is 31 million cubic feet of gas and no reported water from two leases in the Three Bridges field.

The Raton and Vermejo Formations are located within an area thermally mature for oil generation. Raton and Vermejo coals are thermally mature for gas generation along the Purgatoire River drainage system west of Trinidad, Colorado (based on previous vitrinite reflectance studies). These are areas of anomalously high thermal maturation might result from 1) thermal blanket effects of the coals on underlying strata, 2) sampling near Tertiary igneous intrusions, and (or) 3) sources of elevated heat at depth, such as batholiths. Burial history analysis sets the beginning of oil generation for underlying Jurassic through Cretaceous formations at about 67-64 Ma, or near the beginning of the Laramide orogeny. The beginning of thermogenic gas generation is about 26 Ma, or roughly coincident with initiation of the Rio Grande Rift system.