ABSTRACT

Thornwell Field is located in the Lower Miocene producing trend of southwestern Louisiana, in Jefferson Davis and Cameron parishes. It was discovered by Cities Service Oil Company in 1942 and developed into a four well field, producing gas and condensate from a Planulina palmerae sand occurring between 9,600 and 9,700 feet. After depletion and abandonment of these four wells, Austral Oil Company and Pan American Production Company drilled several deep tests and discovered gas condensate in the Marginulina, Camerina and Miogypsinoides sand sections.

The Thornwell Field is a domal structure with an exceedingly complex fault pattern. This pattern consists of a large northeast-striking fault that enters the field from the southwest and breaks up into a system of smaller radial faults as it crosses the dome. The most northwesterly fault block (on the upthrown side of the large fault) is the highest structurally, and each block becomes successively lower around the structure in a clockwise direction. The sediments are considerably thicker on the downthrown side of each fault than on the upthrown side, demonstrating that fault movement was contemporaneous with sediment deposition.

Sand development is much poorer in the higher (northwesterly) fault block than in the lower (southerly) segments. The Camerina sand may be an exception to this generalization since it is known to be well developed in only one fault block. No wells in the lowest fault blocks have penetrated beds older than Marginulina howei.