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The deep Tuscaloosa gas trend of south Louisiana is one of the most significant exploration plays in the United States in recent years. This trend, productive from an expanded Tuscaloosa sand-shale sequence of Upper Cretaceous age, covers a band approximately 30 mi (48 km) wide and 200 mi (322 km) long, from the Texas line on the west and extending past Lake Pontchartrain on the east.
Regional studies begun by Chevron in 1964 demonstrated the probability of an unexplored sedimentary section lying just south of the Lower Cretaceous carbonate bank edge which crosses south Louisiana. Improved regional seismic data later verified the presence of such a unit, termed "the wedge," located between reflectors identified as Upper Cretaceous chalk and Lower Cretaceous carbonates.
The discovery well of the Tuscaloosa wedge was drilled in the False River area in May 1975, when Chevron tested 20 MMCFG/D from a sand at 19,800 ft (6,035 m) in the 1 Alma Plantation, 15 mi (24 km) northwest of Baton Rouge. Chevron confirmed the trend with a discovery in December 1975 at Rigolets field, 125 mi (201 km) southeast of False River field.
The productive section of the Tuscaloosa is interpreted to be a shallow-water deposit built by progradation southward across the Lower Cretaceous carbonate bank edge. Down-to-the-south faulting in this expanded section, together with deep salt movement, has produced most of the structural features that are now productive from the Tuscaloosa.
One hundred and fifteen exploratory wells have been completed along the Tuscaloosa trend, resulting in the discovery of 19 fields. Several apparent discoveries are currently being tested. Proved plus potential reserves discovered through May 1981 are estimated to be approximately 5 TCF. This reserve estimate should increase significantly with continued drilling.
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