Abstract

The Saratoga chalk play in Sabine Parish in the northwestern part of Louisiana is a 300 mi² productive area comprised of the Zwolle and Pendleton–Many–Fort Jessup fields, discovered in the 1920s, with development to 4300 wells in the 1960s and abandoned except for a few stripper wells until recent horizontal well activity (Figs. 1–3).

The Saratoga chalk was deposited on the southern flank of the Sabine Arch during a period of subsidence during the Late Cretaceous (Fig. 4) (Jackson and Laubach. 1991; Ewing, 2009). From the top of the Austin Group, the Taylor Group sequence is the Ozan sand (water-drive), Ozan shale (source rock), Annona chalk (secondary target), and Marlbrook marl, overlain by the Saratoga chalk (productive interval). The seal is the Paleocene Midway shale (Figs. 5–7).

The top Saratoga productive zone ranges from 2400 to 3500 ft in depth. The low permeability chalk is normal-faulted down to the north along a southwest-to-northeast trend and produces from fractured zones in the upthrown fault block (Figs. 8 and 9) (Cameron, 1963; Woods, 1963). The decline curve is surprisingly robust, as the wells produce high-quality 40° gravity oil at commercial rates from fractures with little or no contribution from the matrix (Fig. 10; Table 1). However, the excellent water-drive from the Ozan sand results in production inevitably watering-out over time (Brown, 1978). Slotted liners have proved effective in minimizing the water-coning in recent horizontal wells. No fracking is needed, but acidization can sometimes result in significant production increases.

A Houston-based independent has leased 25,000 acres on the southeast flank of the mature Pendleton Field to drill horizontal Saratoga chalk wells. They completed an initial production (IP) of 325 barrels of oil per day (BOPD) well in 2018 and an IP 590 BOPD well in 2019 (Figs. 11–13; Table 2). Their website shows plans to drill an additional three horizontal wells this year which should firm up commerciality.