Investigations of chemical and stable carbon isotopic character of gases from major fields in the Sacramento basin, California, and the Delaware-Val Verde basins of West Texas and New Mexico indicate a strong possibility of a high-temperature, igneous-type origin for some of these gases.

Geomagnetic surveys of the Sacramento basin indicate the occurrence of 2 types of volcanics. Thin, near surface flows and deep-seated basalt plugs are observed which appear to be related to the occurrence of gas in the basin.

Analysis of coproduced methane and carbon dioxide from a given well yields information concerning the thermal history of the gas. Isotopic equilibrium or quenching temperatures were determined and interpreted on a regional basis.

Gases from the Sacramento Valley are produced from sandstone lenses in alluvial fan-type deposits from Late Cretaceous to Eocene in age. In the south-central part of the basin, the Marysville Buttes constitute a topographic break which has a volcanic plug jutting about 2,000 ft above the surrounding country. Considerable amounts of gas have been produced from sandstone bordering this feature. Secondary folds and faults attending the intrusion exist at a radius of several miles from the core. Gases produced in wells surrounding this cylindrical shaft of igneous rock exhibit a temperature dependence as a function of the distance of production from the central core.

Delaware and Val Verde basin gases from the deep Ellenburger and Devonian formations are dry and composed almost entirely of methane and carbon dioxide. The basin gas data suggest a possible igneous origin, centered about the Marathon thrust zone of the Ouachita structural belt to the southwest.

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