Shongaloo Field: A Recent Smackover (Jurassic) Discovery in the Arkansas-Louisiana State-Line Graben

Abstract

ABSTRACT The new North Shongaloo/Red Rock/Haynesville/East Haynesville field (herein called Shongaloo) is the largest discovery in the mature Gulf Coast Jurassic Smackover play in the past 20 years. Field reserves are 20-30 MMBOE, developed from over 50 producing wells. The field is located within the Arkansas-Louisiana state line graben. The previously under-explored graben bisects the mature state line Smackover play, where exploration dates back to the 1940's. Shongaloo field is an upthrown fault trap within the graben. Vertical separation on the trapping fault ranges from 500 ft. to less than 200 ft. The trapping fault can only be resolved on modern, post-1982 seismic data. Shongaloo field pay is from the Smackover C sand and B carbonate. The C sand is overlain by a key transgressive marker horizon, the marine shale. The marine shale is overlain by prograding carbonate cycles including porous ooid grainstones of the B carbonate. The C sand is a tight gas-condensate bearing sandstone which requires hydraulic fracture stimulation for economic completion. B carbonate grainstone reservoirs have average porosity of 10% and average permeability of 60 md, ranging up to 1,800 md. The majority of the field reserves are from the B carbonate. Two technical methods were advanced in the discovery of the field. First, sub-surface correlations and core descriptions of Smackover facies documented that reservoir rocks follow paleo-shorelines across the graben in the Shongaloo area. Regional stratigraphic study indicates that the vast majority of porous grainstone facies within a mappable cycle of the Smackover B are parallel to and immediately down-dip (< 1.5 mi) of paleo-shorelines. The Smackover B facies in the state line area are associated with paleo-shorelines and are not greatly affected by Jurassic fault movements. Second, the critical trapping fault was resolved by shooting and interpreting modern proprietary seismic data. The discovery of Shongaloo Field demonstrates that significant reserves can be found in mature domestic plays by the application of modern technology and stratigraphic concepts.