Abtract
In 1993,The Department of Energy funded one-year study by the NMBGMR of coal reserves in the San Juan Basin, New Mexico. From this study, the updated demonstrated reserve base (DRB) estimate is 11.24 billion short tons (st) of surface and deep coal. This compares with 4.43 billion st in the Energy Information Administration's DRB for all of New Mexico, and 2.81 billion st for the San Juan Basin, as of January 1, 1993. These new estimates of "remaining" coal resources include significant adjustments for past production and recovery rates (through 1994). The updated estimates also incorporate analyses of available sulfur, heat, and ash content data for characterizing New Mexico's remaining coal resources. Coal quality data (sulfur, ash, and Btu content) were examined along with coal resource data. The preliminary remaining, surface minable DRB estimate for the Bisti field is 872.25 million st of subbituminous low-sulfur coal.

In 1996, the US Geological Survey funded a 1½-year study to evaluate available resources in a four-quadrangle area in the northwest Bisti field. This study differs from the DRB because: (1) it uses GIS for reserve calculation rather than hand calculations and (2) the Fruitland Formation coals are broken down into zones for quality analyses and reserve calculations. The coal quality data were considered in the calculations and past production and technological and accessibility factors were factored in to calculate remaining available resources.

Correlation of the zones required more data be added to the existing database. Assigning zone designations to the different coal beds was a major part of this study.

Using El Paso Natural Gas Co.'s designations, four zones, in descending order were correlated in the Fruitland Formation; the Yellow, Blue, Green, and Red zones. When the Yellow zone is present, the coal-bearing Fruitland averages 172 ft thick. The most laterally consistent coals are in the Red zone at the base of this unit, which differs somewhat from other areas in the Bisti field. The average coal bed thickness in each zone is 6 to 8 ft with maximum coal thickness of 20-30 ft. The Green and Red zones contain the thickest (average) seams. These results compare well with findings from other studies of the entire Bisti field. The weighted quality analyses for each zone indicate a medium sulfur (0.79-0.92 lbs sulfur/million Btu), high ash (15.3-21.52%) coals of subbituminous A rank.

Zone correlation and the use of GIS methods to calculate resources for each zone provides more detailed information than the DRB study, in addition to looking at a smaller geographic area. With the use of GIS, resource estimates can be easily updated when new data become available or restrictions change making this process very useful for future resource evaluation.