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The Viola Limestone has become one of the major exploration objectives in southern Oklahoma. Several fields have been discovered along the northern flank of the Marietta basin in the past five years, and Viola exploration continues to expand along this trend.
Southeast Joiner City field in Carter and Love Counties, Oklahoma, has been an area of recent Viola activity. Structurally, it is a NW-SE trending anticline, bounded on the southwest by a small reverse fault, and on the northeast by the southern limb of the Rock Creek nose.
In July 1979, Chevron USA deepened the J. S. Bates et al 1 to the Viola and completed the well for an IP of 654 BOPD. A total of 11 Viola wells have since been completed in Southeast Joiner City field by Chevron, and one additional well by Petro-Lewis. Total field production from the Viola as of November 9, 1980, was 266,039 bbl.
The Viola Limestone in Southeast Joiner City can be divided into three units, on the basis of log character and sample description. The upper unit, 450 ft (137 m) thick, is composed of very fine to microcrystalline, dense limestone, tan to brown to grayish brown in color. The middle unit, approximately 150 ft (46 m) thick, is characteristically an argillaceous limestone. The lower unit, 450 ft (137 m) thick, is similar to the upper Viola unit, but is characterized by an increase in siliceous limestone with depth. The lowermost 100 to 130 ft (30 to 40 m) of the lower Viola is predominantly dark brown to black, microcrystalline, highly siliceous limestone. Well cuttings from this section commonly contain abundant evidence of fracturing. Low matrix porosity through the entire section, co bined with the lack of correlation between well potential and structural position, indicates that production is related to fracture porosity. Several methods, including both dipmeter and acoustic velocity related fracture logs, have been used to predict or identify fracturing.
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