During the past 2 years (1948 and 1949) four oil fields with exceptional oil-water contacts and abnormally low bottom-hole pressures were discovered in South Arkansas: Bear Creek, Cairo, Loutre Creek, and Pine Tree. The producing reservoir in all of the fields is the Reynolds oolite member of the Smackover formation.

The structure of each field does not appear to be the controlling influence on the reservoir, inasmuch as wells located structurally high produce water, whereas flank wells produce oil. Some geologists have advanced the theory that the various oil-water contacts in each field reflect the presence of individual porous and permeable zones within the reservoir. Although zones such as this could exist, it can be shown that the oil-water contacts in two of the fields display a definite pattern. The writer believes that this pattern is determined by factors outside the confines of the field. These two recently discovered fields are adjacent to major fields which have been producing oil and gas for more than 10 years. In each case the younger field has an inclined oil-water interface sloping toward the older field. The oil-water interface in the Cairo field slopes westward toward the Schuler field; that of the Pine Tree field slopes northward toward the Atlanta field. It is believed that the withdrawals of gas-distillate, oil, and salt water from the Smackover formation in any field will, in a period of years, affect the movement of fluids in adjacent fields and will materially reduce the bottom-hole pressures in those fields. This phenomenon seems to be well illustrated in the Cairo field. The geology of the field and reservoir data are presented.

The Haynesville formation, a new formation name proposed by the Shreveport Geological Society for the thick red sand, shale, and anhydrite beds which overlie the Smackover formation and which some geologists consider as the lower Cotton Valley formation, is also discussed. In this proposed classification the Buckner formation is treated as the basal member of the Haynesville formation. In the Cairo field the relationship of the Buckner formation to the overlying Jones sand is shown.