Geology and fuel resources of the Fruitland Formation and Kirtland Shale of the San Juan Basin, New Mexico and Colorado

Abstract

The San Juan Basin contains sedimentary rocks that range from Cambrian to Holocene in age and are as much as 15,000 feet thick. Upper Cretaceous rocks, which are more than 6,000 feet thick, are composed of intertonguing marine and nonmarine sedimentary rocks deposited during three basin-wide cycles of transgression and regression of an epicontinental sea. The final regression of the sea is represented by the marine Pictured Cliffs Sandstone. Fuel resources of the Fruitland Formation and the Kirtland Shale include uranium, oil, gas, and coal. The uranium occurs in channel sandstone in the Fruitland Formation. Oil and gas occur mostly in small scattered stratigraphic traps. The thickest coal beds occur in the lower part of the Fruitland Formation. The thickest coal occurs adjacent to and southwest of major stratigraphic rises of the Pictured Cliffs Sandstone. Analyses of Fruitland coal samples from rotary-drill cuttings show that the highest quality coal on an as-received basis underlies the northwestern part of the San Juan Basin. As-received Btu values in this area range from about 12,000 to more than 13,000. The coal from the washed drill cuttings is low in moisture content, between 2 to 6%. The ash content of the coal is unusuallymore » high and erratic, ranging from 10 to more than 30%. The lowest ash contents are in the west-central part of the basin; the highest ash contents are in the middle and eastern parts of the basin. The moisture and ash-free values and fixed-carbon ratios of the samples show a well-defined zonation across the basin paralleling the trends of deposition and the basin axis. Statistical analysis indicates that the Fruitland Formation in the San Juan Basin contains approximately 200 billion tons of coal in beds more than 2 feet thick at depths of as much as 4,500 feet. 27 figures, 8 tables.« less