Hydrology of the Upper Cretaceous Fruitland Formation and the producibility of coal-bed methane, San Juan basin, Colorado and New Mexico

Conference · Tue May 01 04:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6663782

Kaiser, W R ^[1]; Swartz, T E ^[2]

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1. Univ. of Texas, Austin (USA)
2. Law Engineering, Austin, TX (USA)

Fruitland coal seams contain 49 tcf of methane, which is produced from abnormally pressured coals in a variety of hydrologic settings. In a study funded by the Gas Research Institute, the authors calculated bottom-hole pressures from wellhead shut-in pressures to map hydraulic head and pressure regime, and estimated vertical pressure gradients to evaluate Fruitland hydrology and its relation to methane producibility. They inferred relative permeability from hydraulic head, pressure regime, and hydrochemistry, and related these hydrologic elements to established production. In the Fruitland Formation, coal seams are the primary aquifers, receiving recharge mainly from the elevated, wet, north and northwest margins of the basin. Formation waters in the north-central part of the basin have low chlorinities and high alkalinities, whereas those in the southern part of the basin are saline Na-Cl type similar to seawater. Regional discharge is to the San Juan River valley in the western part of the basin. Overpressuring in the north-central part of the basin is explained hydrodynamically and is attributed to artesian conditions. They infer enhanced coal-bed permeability where the potentiometric surface is flat and reduced permeability where it is steep. Overpressuring indicates enhanced permeability because permeability in coal seams is stress dependent. In the overpressured region, groundwater is fresh, indicative of an active, dynamic flow system and of permeable pathways. In contrast, connate seawater in the underpressured southern part of the basin implies negligible permeability; strata are too tight to accept and transmit measurable recharge. The basin's most productive coal bed-methane wells are overpressured and occur at hydrologic transitions from a flat to a steep potentiometric surface, overpressuring to underpressuring, and low- to high-chloride formation waters.

• OSTI ID: 6663782
• Report Number(s): CONF-900605--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:5
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
ALKANES
COAL DEPOSITS
COAL SEAMS
COLORADO
CRETACEOUS PERIOD
FEDERAL REGION VI
FEDERAL REGION VIII
FLUID FLOW
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
HYDROCARBONS
HYDROLOGY
MAPPING
MESOZOIC ERA
METHANE
MINERAL RESOURCES
NATURAL GAS DEPOSITS
NEW MEXICO
NORTH AMERICA
ORGANIC COMPOUNDS
PERMEABILITY
POROSITY
RESERVOIR PRESSURE
RESERVOIR ROCK
RESOURCES
SOURCE ROCKS
USA