--> --> Abstract: Exploration for the Arkansas Novaculite Reservoir, in the Southern Ouachita Mountains, Arkansas, by Theodore J. Godo, Peng Li, and Michael E. Ratchford; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Exploration for the Arkansas Novaculite Reservoir, in the Southern Ouachita Mountains, Arkansas

Theodore J. Godo1; Peng Li2; Michael E. Ratchford2

(1) Shell Exploration and Production Company, Houston, TX.

(2) Arkansas Geological Survey, Little Rock, AR.

The Arkansas Novaculite famous for its whetstone characteristic is also an oil and gas reservoir in the Ouachita overthrust belt of Oklahoma and Texas (Caballos Novaculite). Oil and gas fields such as Isom Springs in Oklahoma and McKay Creek, Pinion and Thistle fields in West Texas found reservoirs in this chert section some 30 years ago. The chert reservoir has shown to be productive when it is highly fractured in complex thrust faults. In Arkansas, outcrops of this chert present along the southern side of the Benton uplift often contain a considerable amount of carbonate. The carbonate can be identified at times as highly abraded fossil fragments but otherwise are found as individual calcium carbonate concretion-like masses and also single dolomite rhombs. When leached, it is referred to tripolitic chert and can have porosity measurements ranging to over 50% percent. Assuming the carbonate is leached in the subsurface, the Arkansas Novaculite would have matrix porosity with fractures, which was the concept for the Shell exploration well that drilled Prospect Rattler.

Prospect Rattler was drilled by Shell with the well named the 1-26 Arivett and is located in Pike County, Arkansas. The Arivett 1-26 well spudded in the Mississippian Stanley Shale and reached a total depth of 10,570 in the Silurian Blaylock Sandstone. The well penetrated a complete section of all three members of the Arkansas Novaculite as described in the type section at Caddo Gap Arkansas. This formation had very low dips in an otherwise non-internally faulted section. The well was air/mist drilled and flared several gas shows in sands and novaculite. The upper member of the Arkansas Novaculite contains an unleached carbonate-rich chert section based on cuttings, core analysis, and wireline logging. The results revealed little matrix porosity in the Arkansas Novaculite. However, small amounts of thermally “dead” oil residues or anthraxolite is sometimes present in fractures and some micropores of leached carbonate material. This indicates that a hydrocarbon charge migrated through the Arkansas Novaculite but never accumulated. The vitrinite equivalent reflectance of the Arkansas Novaculite is 3.5%. Even at this high thermal maturity, the middle member shale has up to 4% total organic carbon content and is considered a major source rock. The failure mechanism was most likely a poor reservoir and a poor charge/timing as peak charge occurred before the trap was formed.