Part 4 - Berg - Hughes Center

The uppermost sequence of the Gulfian Series is the Navarro Group consisting of the
Nacotoch and Arkadelphia formations. The Nacatoch is a shallow marine deposit
consisting predominantly of fine- to medium-grained unconsolidated quartz sandstone,
sandy limestone, clay, marl, and shale. Sandstones tend to be glauconitic, ashy and
argillaceous. The Arkadelphia also consists of shallow marine sediments, mainly light
gray chalk/marl with calcareous, micaceous sandstone, and minor volcanic ash. The
Navarro attains a maximum thickness of 600 ft in northwestern Louisiana. It thins
southeasterly and gradually disappears in Natchitoches and Grant Parishes (Cullom et al.,
1962). The Nacotoch is reported to have produced gas in shallow sandstones at depths of
960 ft in Caddo and Bossier Parishes. Where the Navarro produces, the reservoirs are
located from 300 to 2,200 ft in depth. They have porosities of 20 to 28% and permeability
of 200 to 2,500 md.
The Monroe Gas Rock Formation, originally described in the Monroe Gas field by
Stroud and Shayes (1923), is a shallow marine deposit consisting of hard white and gray
sandy chalk that produces in the Monroe Gas field in northeastern Louisiana. Other upper
Cretaceous secondary reservoirs in the Monroe field area are the Arkadelphia, Nacatoch,
and Ozan formations. Sourced through fracture systems from the Smackover, the Monroe
Gas field is the largest gas field in Louisiana with a cumulative production of more than
7.3 trillion cubic feet of gas produced from the field since its discovery in 1916
(Zimmerman and Sassen, 1993). Its areal extent covers more than 365 square miles over
a portion of a 25-township area within adjoining parts of 3 northeastern Louisiana
Parishes: Union, Morehouse, and Ouachita. Depth to the top of the gas rock ranges from
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