Abstract: Stratigraphy and Entrapment of Hydrocarbons in the San Miguel Sands of Southwest Texas

By

James O. Lewis

The San Miguel section of the middle Taylor in the Maverick Basin of the Rio Grande Embayment is a series of overlapping sand bars striking NE-SW. Grain-size plots and core descriptions indicate that these bars developed in a shallow-marine shelf environment. There are as many as five cycles of sand sedimentation, all but one of which is producing. These sands have produced a cumulative of over 50 million bbl of oil since 1948. Over 30 million bbl of oil has been produced from stratigraphic-type fields discovered since 1970. Stratigraphic-type fields have produced over 90% of the total production. Structural traps resulting from differential compaction over volcanic necks account for the remainder.

Torch Field in Zavala County, where the trap is formed by a volcanic neck, and Sacatosa Field in Maverick County, where production is from a stratigraphic trap, are typical examples.

The depth and density of control as well as the subtle expression of the traps suggest that many prospective areas remain.

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