Origin and significance of surface occurrences of natural gas, northern Denver Basin, Colorado

Conference · Wed May 01 04:00:00 EDT 1985 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:5101884

Rice, D D; Threlkeld, C N; Vuletich, A

Natural gas commonly occurs in ground water and has been venturing to the surface from abandoned water wells in the northern part of the Denver basin near urban areas of LaSalle and Greeley. Because these gases pose an explosion and fire hazard, our studies are aimed at determining their origin and source in an effort to help prevent these dangers. Two types of gases have been distinguished on the basis of chemical and isotopic composition. Some of the gases are chemically dry (C/sub 1//C/sub 1/..sqrt../sub 5/ > 0.99) and enriched in the light isotope /sup 12/C (sigma/sup 13/C values range from -73 to -67 ppt). These gases are interpreted to be of biogenic origin; they are being, or have been, generated in an anoxic, sulfate-free environment by decomposition of organic matter within Upper Cretaceous Laramie-Fox Hills aquifer. Other gases contain significant amounts of heavier hydrocarbons (C/sub 1//C/sub 1/..sqrt../sub 5/ values range from 0.76 to 0.88) and are isotopically heavier (sigma/sup 13/C/sub 1/ values range from -49 to -44 ppt). The chemical and isotopic compositions of these gases suggest that they are of thermogenic origin and were generated during intermediate stages of thermal maturity in the deeper part of the Denver basin. In addition, these thermogenic gases are almost identical in both chemical and isotopic composition to those produced from the underlying Cretaceous J sandstone and Codell Sandstone Member of the Carlile Shale at depths ranging from about 2100 to 2300 m (6888 to 7544 ft). The surface gases of thermogenic origin have probably migrated from these deeper reservoirs, and this migration may be related to recent drilling activity in the area.

• Research Organization: Geological Survey, Denver, Colorado
• OSTI ID: 5101884
• Report Number(s): CONF-8506201-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 69:5
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
CHEMICAL COMPOSITION
COLORADO
CRETACEOUS PERIOD
ENERGY SOURCES
FEDERAL REGION VIII
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
ISOTOPE RATIO
MESOZOIC ERA
MINERAL RESOURCES
NATURAL GAS
NATURAL GAS DEPOSITS
NORTH AMERICA
ORIGIN
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SHALES
SOURCE ROCKS
USA