Delineation of Four “Type Producing Areas” (TPAs) in the Fruitland Coal Bed Gas Field, New Mexico and Colorado, Using Production History Data

Reed H. Meek¹ and Jeffrey R. Levine^2
1 XTO Energy, Fort Worth, TX
² Consultant Geologist, Richardson, TX

The Fruitland Coal gas field is a continuous-type hydrocarbon accumulation covering more than 2000 mi² in the San Juan Basin. Reported cumulative production through 2004 is >11.5 TCFG and >236 MBO from over 5270 wells. Individual well cumulative production is highly variable: <1 MMCF to >43,000 MMCF gas; 0 to 31 MBBL Oil, and 0 to 7 MMBBL water. Individual well peak gas rates range from <100 MCFD to >20,000 MCFD. Four distinct NW-SE trending “type producing areas” (TPAs) can be delineated, based upon similarities in reservoir characteristics and production behavior, which are broadly consistent within each TPA, but change dramatically across TPA boundaries. Some key characteristics of each TPA are: TPA1: low to medium gas and water rates, low C₂₊ . TPA2: low gas and water rates, high C₂₊, oil, low CO₂; TPA3: (aka “The Fairway”) very high gas rates, dry CH₄ with high CO₂; TPA4: moderate to high gas and water rates, low C₂₊, moderate CO₂ . In TPA1 and TPA4 water rates tend to decline slowly and peak gas rates are reached after several years of production. In TPA3 water rates decline quickly and peak gas rates occur within the first two years of production. TPA3 and portions of TPA4 were originally overpressured, while TPAs 1&2 are underpressured. Variations in production behavior can be linked to underlying geological controls, especially coal rank, coal thickness, pressure regime, and hydrodynamics. These variables affect the primary controls on gas production: hydrocarbon content and composition, initial reservoir pressure, initial water saturation, and cleat permeability.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005