Bayou Middle Fork field, Claiborne Parish, Louisiana, is located in north-central Louisiana near the Arkansas-Louisiana border in an area known as the "State-Line trend" of the Upper Jurassic Smackover Formation. Smackover production in the area is associated with a complex fault system masked by approximately 10,000 ft (3,000 m) of younger sediments. A geophysical program combined with geologic studies indicated a faulted, deep-seated east-west-trending anticline. On the basis of this evidence, Cities Service Co. drilled a test well on the structure and discovered the Smackover reservoirs at Bayou Middle Fork field in March 1975.

Core and sample studies made as the field developed showed the Smackover at Bayou Middle Fork field to be a limestone composed mainly of oolites, hardened pellets, pisolites, oncolites, and micrite. This limestone has been divided into three units designated as the Smackover A, B, and C. The general environmental setting that produced these sediments varied from low- to high-energy conditions over a broad, shallow, gradually south-sloping marine shelf. This environmental setting underwent continual minor sea-level fluctuations and structural changes, producing an interfingering and mixing of the various carbonate sediments. One major change occurred as sea level completely receded. The shelf was exposed to supratidal conditions which resulted in the deposition of evaporitic and contin ntal sediments. This regression ended Smackover "C" deposition and produced the Buckner "B" member of the stratigraphic section, which was followed by a partial transgression and subsequent regression resulting in the Smackover "B" and "A" being deposited in an offlap sequence. This second withdrawal of the sea ended Smackover deposition and again produced conditions for accumulation of supratidal and continental sediments.

Porosity preserved within the oolitic rocks is primary intergranular and has been enhanced by leaching of the oolites. Effective porosity varies from a low of 8% to a high of 23.7% and permeability ranges from less than 1 to 270 md. During early development of the field, the porosity and water values from log analysis indicated the possibility of substantial water production. However, as wells were completed, no water was produced; scanning electron microscope and petrographic work revealed the presence of microporosity containing irreducible water.

Smackover production at Bayou Middle Fork field is from three separate reservoirs, the Smackover "C," and upper and lower "A." The lower Smackover "A" reservoir, the largest of the three, contains volatile oil, that through primary production is produced by solution gas drive, with recovery of only 20% of the oil in place. To provide pressure maintenance, a water-drive system was chosen. It is estimated that an additional 20% of the oil in place will be produced by the waterflood program.

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