Relation of natural gas composition to thermal maturity and source rock type in San Juan Basin, Northwestern New Mexico and Southwestern Colorado
San Juan Basin is a roughly circular, asymmetric structural depression located in Northwestern New Mexico and Southwestern Colorado. Ultimate recoverable reserves of predominantly nonassociated gas are present in the structurally low part of the central basin. The major producing intervals are low-permeability sandstone reservoirs in the Upper Cretaceous Dakota Sandstone, Mesaverde Group, and Pictured Cliffs Sandstone. Lesser amounts of oil and/or gas are produced from Pennsylvanian, Jurassic, and Cretaceous rocks along the southern and western flanks of the basin. The gases display a trend of becoming isotopically heavier and chemically drier with increasing depth. These changes are assumed to be the result of thermal cracking processes, and the gases are interpreted to have been generated during the mature and post-mature stages of hydrocarbon generation. However, there is considerable scatter in the data which is interpreted to result from a difference in source rock type. Gases generated from nonmarine (humic) source rocks are isotopically heavier and chemically drier than those generated from marine (sapropelic) source rocks at equivalent levels of maturity. The gases also become isotopically heavier and chemically drier to the northeast, following the trend of increasing maturity of all units in that direction. The increase in maturity is attributed to a combination of greater burial depth and a higher geothermal gradient resulting from batholiths to the north in the San Juan Mountains area. Maximum burial and heat flow occurred during the Oligocene, which probably coincided with peak hydrocarbon generation.
- Research Organization:
- U.S. Geological Survey, Denver, CO
- OSTI ID:
- 6884582
- Journal Information:
- AAPG Bull.; (United States), Journal Name: AAPG Bull.; (United States) Vol. 67:8; ISSN AABUD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
030200* -- Natural Gas-- Reserves
Geology
& Exploration
033000 -- Natural Gas-- Properties & Composition
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CHEMISTRY
COLORADO
CONDENSATES
CRACKING
CRETACEOUS PERIOD
DECOMPOSITION
DISTRIBUTION
ENERGY SOURCES
EXPLORATION
FEDERAL REGION VI
FEDERAL REGION VIII
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS CONDENSATES
GAS FUELS
GASES
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
GEOTHERMAL GRADIENTS
GEOTHERMOMETRY
ISOTOPE RATIO
LIQUIDS
MATURATION
MESOZOIC ERA
MINERAL RESOURCES
NATURAL GAS
NATURAL GAS DEPOSITS
NATURAL GAS LIQUIDS
NEW MEXICO
NORTH AMERICA
ORIGIN
PERMEABILITY
PETROLEUM
PETROLEUM GEOLOGY
PYROLYSIS
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SOURCE ROCKS
SPATIAL DISTRIBUTION
TEMPERATURE GRADIENTS
THERMAL CRACKING
THERMOCHEMICAL PROCESSES
USA