Print this pageR. A. Lamarre1, T. Pratt2, and T. D. Burns3
1Texaco Exploration and Production, Inc., Denver, CO
2 TICORA Geosciences, Inc., Arvada, CO
3River Gas
Corp., Tuscaloosa, AL
ABSTRACT: Reservoir Characterization Study Significantly Increases Coalbed Methane Reserves At Drunkard's Wash Unit, Carbon County, Utah
The Drunkard’s Wash Unit produces coalbed methane from Upper Cretaceous coals within the Ferron Sandstone Member of the Mancos Shale in Carbon County, Utah. During November, 2000, the field produced 215 MMCFD from 349 wells at an average depth of 2800 feet. The field has produced 190 BCF since initial production in January, 1993.
Coalbed methane reserves are commonly calculated from data obtained from samples with bulk density of less than 1.75 g/cm3. This density typically defines the rock “coal” that contains at least 50% by weight carbonaceous material (Levine, 1993). However, recent studies (Mavor and Nelson, 1997) have shown that adjacent lithologies with densities greater than 1.75 g/cm3 can also contain significant volumes of methane. A comprehensive core sampling program of the coals and adjacent shaley coals and carbonaceous shales was carried out in the Birkinshaw # 18-149 well in Section 18, T14S, R9E in Drunkard’s Wash Unit. The purpose of the sampling program was to sample all organic -bearing lithologies adjacent to the clean coals to determine if they also contain methane.
The well contains 15.5 feet of pay using a bulk density cutoff of 1.75 g/cm3. However, using a cutoff of 2.55 g/cm3 results in 53.5 feet of pay due to the inclusion of higher density rocks. Compares the gas content versus the moisture plus ash content from 20 core samples. Regression analysis of this data indicates that the clean coal (ash and moisture-free) contains 844 standard cubic feet of gas per ton of coal (scf/t). The gas content is zero at ash and moisture contents of 93%. This type of regression analysis is valid on these samples because we sampled the full range of densities within the coal-bearing interval.
The average in-situ gas content is 622 scf/t when a density cutoff of 1.75 g/ cm3 is used. However, the 53.5 feet of pay resulting from a cutoff of 2.55 g/cm3, has an average in-situ gas content of 322 scf/t. Based on 160-acre well spacing, gas-in-place for this well increases from 3.1 BCF to 6.6 BCF when the higher bulk density cutoff is used. This is an increase of 113 % more gas-in-place. Fifty three percent of the gas-in-place in this well is in lithologies with densities greater than 1.75 g /cm3.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado