ABSTRACT

Although the Haynesville field is 30 years old, Jurassic production was not discovered until November, 1944, when oil was found in the Taylor sand at a depth of 8835-8920 in the basal portion of the Schuler formation, Cotton Valley group. Within the next two years oil and gas were also discovered in the Camp sand of the Schuler formation, and in the Smackover limestone.

The principal Jurassic producing horizon is the "B" zone, which occurs in the upper Smackover at an average depth of 10,000', and is made up of oolitic limestones with some sandstone. An interval of 40 to 100 feet of variegated shale and anhydrite separates the "B" zone from the overlying "A" zone, a porous oolitic limestone which produces oil and gas in a limited portion of the field. The "A" zone thickens from a feather-edge to approximately 400 feet downdip. Above the "A" zone is a section of pink to red sands and shales with anhydrite which attains a thickness of 400 feet. A regional unconformity separates this sequence from the overlying Cotton Valley group. The entire section between the base of the Cotton Valley and the top of the "B" zone is referred to the Haynesville formation. The Haynesville, together with the Smackover and underlying Norphlet formation, comprise the Louark group, a name proposed and adopted by the Shreveport Geological Society.

The Cotton Valley group, consisting of 2500 feet of sands, shales and thin limestones, has been divided into a lower Bossier formation and an upper Schuler formation. An unconformity between the Bossier and Schuler formations, marking a period of regression and transgression, is discussed. A stratigraphic break at the top of the Cotton Valley is thought to be a regional unconformity.

Three structural maps are presented, one on the Taylor sand, the other two on the "A" and "B" limestones. The Cotton Valley map indicates a structure of low relief, while the deeper maps indicate fauling with much steeper dip.

As of September 1, 1951, seven wells were producing from the Taylor sand, and the one Camp sand well was shut in. Twelve wells were producing from the "A" zone, and 38 were completed in the "B" zone. All Jurassic wells are drilled on north-south 80 acre units. Cumulative production from the Cotton Valley sands amounted to 1,231,049 barrels to August 1, 1951. The "A" and "B" zones had produced a total of 5,757,921 barrels of oil and distillate to August 1, 1951, the bulk of which was from the "B" zone. The "A" zone had produced about 7-1/2 million MCF gas, as compared to almost 60 million MCF for the "B" zone.

The paper is intended as a summary of facts and ideas contributed by a number of geologists. Most of the information has been published previously, and interpretation is subject to revision.

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