Methane recovery from New Mexico coals

Using a newly developed technique, the methane content of 30 coal samples from 14 different sites in the San Juan Basin has been determined. The chip-desorption technique is faster and significantly cheaper than traditional, core-sample based delineation of coal bed methane. The methane content of the Fruitland coals in the San Juan basin was found to range from 1 to 6 cc/g without correction for shale that may be collected along with the coal. Laboratory studies have been initiated to determine the accuracy of a lost-gas correction scheme that is required to account for the rapid gas-desorption from these coal chips. Early results appear to show that the correction model is followed for the first 25 to 50 percent of the gas desorption for wet coals. The effects of surface diffusion and bimodal pore structure on the total gas desorption rate are being investigated in order to develop a physically realistic model that is applicable to long-term production models. Adsorption studies have shown that the methane storage is associated with the micropore (< 20 A) structure of the coal.