About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 36 (1986), Pages 457-470

Origin of Gaseous Hydrocarbons in the Sparta Aquifer in Brazos and Burleson Counties, Texas

Ethan L. Grossman, Robert W. Hahn, Steven J. Fritz (1)

ABSTRACT

Gaseous hydrocarbons occur in high concentrations in the Sparta aquifer in eastern Texas. To test whether these gases migrated from deep petroleum or gas reservoirs, comprehensive chemical and isotopic analyses were performed on the gaseous hydrocarbons and associated waters from 24 wells (40 - 2010 ft) in the Sparta aquifer and one well in the overlying Yegua aquifer. Similar analyses were also performed on gaseous hydrocarbons from petroleum and gas production wells in the area.

Methane contents in the waters are highly variable, ranging from below detection limit to supersaturated with greater than 500 ml/1 in the head gas. The only other gaseous hydrocarbon detected in the groundwaters is ethane, which occurs in the head gas in concentrations of up to 0.4 ml/l. Six wells had gaseous hydrocarbon concentrations high enough to permit determination of 13C/12C ratios. The carbon isotopic compositions range from -62 to -52^pmil. These data, along with high C;1C2+, ratios, provide evidence that the gaseous hydrocarbons are derived predominantly from biogenic sources. However, the isotopic enrichment of the Sparta gases relative to Yegua gas (^dgr13C = -74^pmil) suggests that significant amounts of 13C enriched thermogenic gases may be leaking into the aquifer from deep-seated hydrocarbon deposits.

The chemistry of the groundwater reflects input of carbon through the oxidation of humus and lignite, and to a lesser extent through the oxidation of methane and the fermentation of organic compounds.


Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24