ABSTRACT

The Tuscaloosa trend of south-central Louisiana is one of the most active and highly potential deep gas plays in the United States today. The trend covers a band 275 mi long and 30 mi wide. It extends from the Louisiana-Mississippi border, northwesterly through Lake Pontchartrain to Baton Rouge, and continues westerly through Vernon and Beauregard Parishes to the Louisiana-Texas border (fig. 1). To date there have been 15 new fields discovered and two potential new discoveries in the trend (fig. 1). In the last four years a total of 142 wells have been drilled to an average depth of 18,800 ft to test sandstones within the Tuscaloosa Formation (Upper Cretaceous). More than 4 million acres are now under lease in the trend.

The center of the play is located north of Baton Rouge where the Baton Rouge mega-structure (figs. 2 and 4), a giant structural complex at least 20 mi long and approximately 15 mi wide, is emerging as the dominant feature of several exceptionally large structural features. Six new discoveries, one potential new discovery and one new field reservoir extension, are located on this mega-structure. Other fields surely will be found within the 300-sq-mi area presently indicated to be productive. The Judge Digby structure, located west of the Baton Rouge mega-structure (F in fig. 2), is a slightly smaller feature containing major gas reserves. To the east of the Baton Route mega-structure is the Denham Springs structure now being evaluated by the Amoco #1 Barnett Heirs, presently drilling below 14,600 ft.

Potential reserves on these features total approximately 17 trillion cubic feet of gas and one billion barrels of distillate.

The Tuscaloosa play began in May 1975, with the discovery of False River field by Chevron #1 Alma Plantation, located approximately 12 mi northwest of Baton Rouge. This well tested gas at the rate of 20 million cubic feet per day from a Tuscaloosa sand at 19,800 ft (figs. 3 and 4). The trend was confirmed with the completion of Chevron #1 S.L. 6646 in December 1975, as the discovery well for Rigolets field located approximately 120 mi southeast of False River field near the Louisiana-Mississippi state line. Subsequent discoveries include North Bayou Jack, False River Reservoir 'B', Moncrief and South Moncrief fields.

A major development occurred on August 13, 1977, when the Chevron #1 Parlange blew out at a depth of 21,346 ft (figs. 4 and 5). This well, located eight miles northwest of the False River discovery, was later brought under control and produced gas into the Florida Gas sales line for 60 days at the rate of 140 million cubic feet of gas per day. This production rate clearly established excellent reservoir conditions to complement the giant structures, and a new deep gas frontier had been established. This discovery was named Judge Digby field.

Shortly thereafter a significant discovery was made at Port Hudson field, located approximately nine miles northeast of False River field. The Amoco #1 Georgia Pacific flowed 4.8 million cubic feet of gas per day plus 696 barrels of distillate and encountered 161 ft of net gas sand (figs. 4 and 6).

In July 1978, Irene field was discovered on the Baton Rouge mega-structure with the completion of the South Louisiana Production Company #1 Kizer, located 12 mi northeast of False River. The #1 Kizer, encountered 68 ft of net gas sand and was tested at the rate of 10 million cubic feet of gas per day plus 228 barrels of distillate. One month later Hunt Petroleum Corporation completed its #1 Trans Match, located midway between False River and Irene. The #1 Trans Match was tested at the rate of 14.1 million cubic feet of gas per day plus 650 barrels of distillate.

Subsequent new discoveries include Fort Pike, with the completion of Natomas #1 S.L. 7260, located six miles west of Rigolets field. This well tested 11 million cubic feet of gas per day. Natomas recently completed its #1 S.L. 7186, located in Lake Pontchartrain, and tested 92 barrels of distillate plus 2.1 million cubic feet of gas. The most significant recent discovery is the Amoco and Banner #1 Hurst located six miles north of Judge Digby field. The well is being completed after testing 336 barrels of distillate per day plus 11.8 million cubic feet of gas per day.

The discovery wells to date in the Tuscaloosa trend have been drilled to an average depth of 18,850 ft. A summary of these discoveries including well name and location, total depth, perforations and tests is shown in table 1.

As of May 1, 1979, more than 70 development wells have been completed or are presently drilling or active. Depth of these development wells ranges from 17,000 ft to 23,500 ft. Average dry hole cost is approximately $3.5 to $4 million; average drilling time is from 125 to 200 days; average completion time is approximately 30 days to 45 days; and average completed well cost ranges from $4 million to $6.8 million.

Since the discovery of False River field there have been 56 wildcats drilled in the trend. At least 12 of these wells

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were drilled on the shelf, behind the the barrier reef and did not evaluate the Tuscaloosa sand at its optimum position.

Drilling activity in the trend has increased considerably in the past few weeks, and it is expected to continue. Within the next six months operations will probably have commenced on at least 45 additional wells across the trend. Truly, the Tuscaloosa trend of south-central Louisiana is one of the most active and highly potential deep gas plays in the United States today!

Figure 1. TUSCALOOSA TREND SOUTH CENTRAL LOUISIANA INDEX MAP

Figure 2. TUSCALOOSA TREND SOUTH CENTRAL LOUISIANA AREA MAPPED

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Figure 3. TYPE LOG TUSCALOOSA TREND SOUTH CENTRAL LOUISIANA

Figure 4. TUSCALOOSA TREND SOUTH CENTRAL LOUISIANA "TOP TUSCALOOSA SAND"

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Figure 5. BATON ROUGE MEGA-STRUCTURE NORTH-SOUTH CROSS SECTION

Figure 6. BATON ROUGE MEGA-STRUCTURE EAST-WEST CROSS SECTION

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Table 1. TUSCALOOSA TREND - SOUTH CENTRAL LOUISIANA

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