Part 4 - Berg - Hughes Center

The limestones are 10 to 100 ft thick and are interbedded with shales that are 10 to 30 ft
thick. Similar to the other underlying Cotton Valley units, the Knowles in Louisiana
grades northward into terrestrial red beds of the Schuler Formation in Arkansas, and in
some areas of Louisiana it is overlain conformably by the Cretaceous Hosston Formation.
Schuler Formation (Dorcheat Formation)
The Schuler Formation consists mainly of shale, but in Arkansas toward the pinch-
out of the unit it contains increasing amounts of sandstone (Forgotson, 1954). In fact,
near the pinch-out, the formation is entirely sandstone and pebble conglomerate. In
southern Arkansas, there is a predominance of nearshore to nonmarine lenticular, fine-
grained, red and gray sandstone and shale or mudstone. The lenticular red beds probably
accumulated as coastal plain deposits on the coastal side of a lagoon. The red terrigenous
siliciclastic sediments extend south in northeastern Louisiana and western Mississippi,
where the Schuler is almost totally sandstone. According to Forgotson (1954), a large
delta was responsible for the thickness and distribution of the sandstones in northeastern
Louisiana and western Mississippi. The Hosston Formation overlies the Schuler
Formation disconformably.
Approximately 45 reservoirs exist within the Cotton Valley Group. The optimum
producing reservoirs consist of fine- to medium-grained, massive barrier bar sandstone
and shallow marine oolitic limestone of the Terryville and Knowles formations,
respectively. In northern Louisiana, depth to the top of the pay zones range from 3,600 to
14,500 ft. Net pay of the reservoirs ranges from 10 to 60 ft with porosities of 9 to 18%
and permeabilities of 1 to 300 md. The produced hydrocarbons are typically 41º API
gravity oil, condensate, and gas.
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