Aliphatic acid anions in oil-field waters: implications for origin of natural gas
Concentrations of short-chain aliphatic acid anions (acetate, propionate, butyrate, and valerate) in 95 formation-water samples from 15 oil and gas fields in the San Joaquin Valley, California, and in the Houston and Corpus Christi areas, Texas, show three temperature regimes. The aliphatic acid anions of formation waters in zone 1 (subsurface temperatures lower than 80/sup 0/C) are characterized by concentrations less than 60 mg/L. The concentrations of aliphatic acid anions in zone 2 (temperatures 80 to 200/sup 0/C) are much higher (up to 4900 mg/L) than in zone 1, and decrease with increasing subsurface temperatures and age of their reservoir rocks. No aliphatic acid anions are believed present in zone 3, the temperatures are higher than 200/sup 0/C. Microbiologic degradation of acetate and dilution by mixing with meteoric water most probably explain the composition and concentration of aliphatic acid anions in zone 1. The trends in zone 2 and the absence of acid anions in zone 3 are explained by thermal decarboxylation of these acid anions as in the reaction: CH/sub 3/COO- + H/sub 2/O ..-->.. CH/sub 4/ + HCO/sub 3//sup -/. The aliphatic acid anions mainly result from the thermocatalytic degradation of kerogen. Decarboxylation of these acid anions to the components of natural gas is believed to occur mainly in the reservoir rocks. Evidence for the formation of natural gas from decarboxylation of acid anions is provided by the delta C/sup 13/ values of total bicarbonate and CH/sub 4/ and the good correlation between the proportions of these anions in formation waters (94% for acetate, 5% for propionate, and 2% for butyrate) and their decarboxylated gases in the natural gas produced (90% for methane, 5% for ethane, and 2% for propane).
- Research Organization:
- Geological Survey, Menlo Park, CA
- OSTI ID:
- 5698076
- Journal Information:
- Am. Assoc. Pet. Geol. Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol. Bull.; (United States) Vol. 62:12; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
030200* -- Natural Gas-- Reserves
Geology
& Exploration
ACETATES
ALKANES
ANIONS
BITUMINOUS MATERIALS
CALIFORNIA
CARBONACEOUS MATERIALS
CARBOXYLIC ACID SALTS
CARBOXYLIC ACIDS
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMISTRY
CRYOGENIC FLUIDS
DECARBOXYLATION
ENERGY SOURCES
ETHANE
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOCHEMISTRY
GROUND WATER
HIGH TEMPERATURE
HYDROCARBONS
HYDROGEN COMPOUNDS
INTERSTITIAL WATER
IONS
KEROGEN
MEDIUM TEMPERATURE
METHANE
MONOCARBOXYLIC ACIDS
NATURAL GAS
NATURAL OCCURRENCE
NORTH AMERICA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORIGIN
OXYGEN COMPOUNDS
PROPANE
PROPIONIC ACID
SOUTHWEST REGION
TEXAS
THERMAL DEGRADATION
USA
WATER
WESTERN REGION