Tennessee gas field brings Eastern Overthrust new life

G. Alan Petzet
Exploration Editor

The Eastern U.S. Overthrust Belt has gained an E&P company in its southern reaches while seeing de-emphasis from a long time player in more northerly areas.

A gas field discovered in the early 1980s in northeastern Tennessee is nearly ready to be placed on production. It would be the first commercial gas production in the southern portion of the belt, which extends more than 1,000 miles from Alabama to New England.

Tengasco Inc., Knoxville, a public company since mid-1995, began laying a pipeline from Swan Creek field in Hancock County, Tenn., to a nearby utility. The line is to be extended later to connect with a major transmission line. If the field performs well, it could recapture attention for the belt, which has seen relatively little drilling for 10 years. Columbia Natural Resources Inc., Charles- ton, W.Va., the main player in the northern belt, has de-emphasized exploration there. Columbia discovered numerous fields that produced mainly from Devonian Oriskany along the belt in West Virginia the past two decades.

Columbia, reorganized since its parent emerged from bankruptcy, has downsized E&P and refocused the main thrust of its exploration program on the Cambrian Rose Run sandstone play in Ohio. It still operates gas production and storage fields in the belt in several states.

The Eastern Overthrust belt is a highly folded and faulted area of the Appalachian basin that extends eastward from the Allegheny structural front. The belt's eastern extent was not defined, and some workers suggested it might continue across the Valley and Ridge and Blue Ridge provinces and as far east as the Piedmont province and the Atlantic coastal plain (OGJ, Dec. 6, 1982, p. 191).

Tennessee action

Tengasco has five wells capable of producing gas from Cambro-Ordovician Knox in Swan Creek field, southwest of Sneedville in Hancock County, Tenn., about 10 miles south of Lee County, Va. It hopes to drill five more wells by yearend.

It began laying a 30-35 MMcfd, 23 mile, 6 in. gas pipeline to Rogersville, Tenn., early last month. Torch Inc., Belle Chasse, La., has the contract.

Tengasco plans to start production later this year. Initially a gas utility in neighboring Hawkins County will take 8-9 MMcfd and transport any excess gas to Tenneco Energy affiliate East Tennessee Natural Gas Co.

Tengasco in 1997 plans to extend its pipeline 17 miles east of Rogersville to a direct connection with East Tennessee. It has also proposed to build a lateral to Sneedville, Tenn., and a pipeline from Swan Creek field west to Tazewell, Tenn., next year. Hancock and four or five adjacent counties have industrial and commercial businesse but no gas service.

Tengasco is also rigging up to participate in gas futures markets.

Gas from the Knox

Tengasco has drilled three wells in Swan Creek field and operates two wells Amoco drilled in 1982. The field lies along the Clinchport thrust fault on the Clinch River (Fig. 1 [125942 bytes]).

The Amoco-Anschutz 1 Paul Reed well went to 10,569 ft in Lower Cambrian in 1982. It cut 68 ft of gas production in six Knox intervals at 4,414-4,624 ft overall. On a recent test the well flowed gas at the rate of 4.8 MMcfd in 72 hr on a 1/2 in. choke with 840 psi FTP. Shut-in tubing pressure was 1,800 psi.

The 1 Sutton, 2 miles to the northeast, recently flowed 1.2 MMcfd on a 1/2 in. choke with 120 psi FTP from Knox at 4,404-16 ft. SITP is 1,800 psi, and TD is 5,015 ft.

Tengasco's 2 G. Patton well encountered oil and gas in upper and middle Ordovician and 34 ft of gas pay in Knox in three intervals at 4,590-4,890 ft overall earlier this year. It flowed gas at the rate of 1.5 MMcfd in 72 hr on a 1/2 in. choke with 250 psi FTP and 1,800 psi SITP.

Tengasco's 1 Warren Reed encountered an oil horizon in Trenton that tested 36 b/d of 45° gravity oil at 1,760-70 ft. It also had a productive gas interval in Knox at 4,745-50 ft. It is to be deepened to penetrate additional Knox zones. The oil, if developed, would likely involve twin wells.

Tengasco drilled the B. Colson well to 5,000 ft. It encountered 30 ft of gas in Trenton at 1,560-90 ft and 10 ft of oil at 1,830-88 ft and 27 ft of oil and gas in Trenton at 2,582-2,614 ft. It cut 118 ft of significant gas shows in Knox. Perforated in four zones at 4,450-4,520 ft, it flowed 1.25 MMcfd of gas on a 1/2 in. choke with 185 psi FTP.

The dry gas analyzed 1.05 MMBTU/Mcf. The newer wells cost $175,000 for dril- ling/completion plus about $30,000 for surface equipment.

Overthrust geology

Knox production in most parts of the Appalachian basin has been encountered within 200 ft of the top of the formation, said Tengasco geologist Michael McCown.

The primary production to date in Swan Creek field has been in a 300 ft section some 400-450 ft from the top of Knox (Fig. 2 [93567 bytes]). No water has been found.

The productive intervals are a light grey to tan dolomite with a relatively high concentration of calcarenite. Porosity ranges from 6-18% with a number of the pay zones being fracture enhanced, McCown said.

Seismic data indicate the presence of extensive "bright fractures" (OGJ, July 1, 1996, p. 132) existing along this structural trend, which strikes northeast into Virginia, he said.

Play in the making?

Tengasco visualizes a field development that encompasses several dozen possible locations. A ridge southwest of the Coulson well divides the locations into two roughly equal groups.

The company has acquired about 800 acres on the same structure in Claiborne County to the southwest.

Well elevations in the area have been 1,400-1,600 ft. The pipeline route to Rogersville, much of which is on Tennessee Valley Authority power line right of way, reaches high points of 1,700-2,000 ft.

Independent engineers estimated a volumetric 86.852 bcf of possible gas in the Swan Creek structure, said Elizabeth Stewart, Tengasco petroleum engineer. She sees a 20 year well life with declines of 25% in the first 18 months, then 7.5%/year.

Tengasco holds about 10,000 acres on the Swan Creek structure and another 20,000 acres in the Kyle's Ford area to the northeast, along the ARCO LO-3 seismic line near the Virginia line.

McCown said Tengasco sees what it believes is the Cambrian Rome formation on seismic at about 10,000 ft under the axis of the Swan Creek feature.

Tengasco also has the rough data TC-1 seismic line along highway 25E between Tazewell and Bean Station southwest of Swan Creek. All seismic lines are 2D data from the early 1980s.

The company has future prospects in mind in Blount, Anderson, Loudon, and Roane counties and as far south as northern Alabama.

A sixth well at Swan Creek is the Chevron 1 Reed, the westernmost in the field. Drilled in 1986 by Eastern American, it has two gas zones in Knox, McCown said.

Chevron has about 1,500 acres under lease in the general area. Chevron appeared not to have immediate plans in the area at OGJ presstime.