Part 4 - Berg - Hughes Center

Caddo Parish, it attains a thickness of 620 ft on top of the Brownstown Formation. A
number of reservoir quality sands exist within the Tokio and produce in Caddo, Bossier,
and Webster Parishes. Located at depths of 2,400 to 3,100 ft, these reservoirs have
porosities of 20 to 35% and permeabilities of 200 to 450 md. The overlying Brownstown
Formation consists of dark gray calcareous clay or marl with sandy marl and fine-grained
sand. The reservoir quality sands are reported to be located near the top of the formation
in Caddo Parish (Ogier, 1963).
On the southern edge of the basin and overlying the Washita-Fredericksburg and
parts of the older Cretaceous barrier reef system (Glen Rose), a band of Austin Chalk
extends from Texas through Vernon Parish to the southwestern corner of Mississippi and
beyond to the southeast. In this area of southernmost north Louisiana, approximately 50
miles south of the nearest shallow piercement salt dome in the North Louisiana Salt
Basin, the Austin Chalk consists primarily of compacted argillaceous foraminiferal and
coccolith limestone (biomicrite) with interbeds of marl and bentonitic marl. Hydrocarbon
targets in the chalk include the fractured basal section of the Austin. The hydrocarbon
bearing target section is approximately 180 to 400 ft in thickness and encountered at drill-
depths of 12,500 to 17,500 ft (Zimmerman, 1998). According to Zimmerman (1998), the
reservoirs within this Texas-Louisiana trend generally have a dual pore system which is
derived from a microporous matrix and fractures that yield low porosity and low
permeability reservoirs with high water content and less than 50% residual oil
saturations. In-situ matrix porosities and permeabilities are generally less than 5% and
0.05 millidarcies, respectively. Reservoir development is through long lateral (horizontal)
wellbores.
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