EXPLORATION Discoveries mount in E. Texas Cotton Valley pinnacle reef play

May 6, 1996
G. Alan Petzet Exploration Editor Where Cotton Valley Reef Wildcatting is Busy [18632 bytes ] Another sizable discovery and more operators are popping up in the expanding East Texas Jurassic Cotton Valley pinnacle reef gas play. Sonat Exploration Co., Houston, reported a large discovery and sizable participation in the play in late April. Sonat and its partners join Marathon Oil Co., which has dominated the play the past few years.
G. Alan Petzet
Exploration Editor

Another sizable discovery and more operators are popping up in the expanding East Texas Jurassic Cotton Valley pinnacle reef gas play.

Sonat Exploration Co., Houston, reported a large discovery and sizable participation in the play in late April. Sonat and its partners join Marathon Oil Co., which has dominated the play the past few years.

Sonat started sales Apr. 21 from the 1 Fountain, a new field discovery in northwestern Leon County between McSwane and Branton gas fields. The discovery flowed at a rate of 30.3 MMcfd of gas with 5,060 psi flowing wellhead pressure. TD is 14,379 ft.

Sonat estimated reserves at the well, possibly the only one to be drilled into the reef, at 70-80 bcf of gas.

Sonat in late April formed a joint venture to explore the trend with UMC Petroleum Corp., Houston, and two smaller private companies, Aspect Resources and MB Exploration.

A map of the combined acreage was not available from Sonat at press time, but the accompanying map indicates UMC's position as presented to financial analysts earlier this year.

Sizing up the play

Operators use 3D seismic to image reefs at 14,000-15,000 ft, but to a degree the lack of rapid expansion in the play before second half 1995 is due to the time and experience required to properly process and interpret the data, writes Scott Montgomery in an E&P note in the May 1996 AAPG Bulletin.

Exploratory drilling in the play in 1995-96 has centered on Leon and Robertson counties (see map, OGJ, Aug. 28, 1995, p. 101).

The play's scorecard appears to total at least seven announced reef discoveries including Sonat's since 1980, including six-McSwane, Branton, Pearwood, Kenwood, Bohlwhite, and Eichelson fields-operated by Marathon. At least four more wells, operated by Marathon, Am- oco, American Cometra, and Zackson Resources, have undergone completion at- tempts or have potential as indicated by cementing of production casing.

One operator points out that discovery of 20 reefs EUR averaging 50 bcf would represent a contribution of 1 tcf to U.S. gas supplies.

Joint venture search

The companies participating in the Sonat-UMC venture jointly own acreage in an area of mutual interest across seven counties.

The companies have committed a combined 161,000 acres to the joint venture. Sonat said it holds a further 30,000 acres not part of the joint venture.

Sonat holds interests in about 261,000 acres in the western and northwestern shelf areas of the East Texas Salt basin, of which 191,000 acres are in the pinnacle reef trend. It said it is the pinnacle reef play's largest acreage holder and continues to acquire leases.

The joint venture, with Sonat as operator, plans to acquire an additional 150 sq miles of 3D seismic data. Acquisiton of 33 sq miles of the 3D data was under way.

Sonat said the 1 Fountain discovery well is on the first drilled of 16 seismic anomalies on a block dedicated to the joint venture. Seismic interpretation is under way of additional anomalies on another block just to the north.

Expansion scope large

The play seems to have considerable scope for ex- pansion to the north and northeast.

Zackson Resources Inc., Houston, set pipe to TD at a 15,100 ft pinnacle reef wildcat. The 1 Manzikert is about midway between Marathon's Brounkowski and Riley Trust pinnacle reef gas discoveries five miles apart.

Petroleum Information shows that the 1 Riley Trust, the Bohlwhite field opener, produced 1.55 bcf of gas and 13 bbl of condensate during October through January.

Zackson has drilled one other deep wildcat and staked a third in Robertson County.

Amoco is drilling a second deep wildcat south of Pearwood (Poth) field and just east of Marquez in Leon County. The wells are permitted to 18,500 ft, and Amoco has not revealed results.

Marathon, which holds about 40,000 net acres in Robertson, Leon, and Freestone counties, has acquired 280 sq miles of seismic and had three rigs running in late April. It plans to have drilled six exploratory wells during 1996.

Marathon's gross production is about 60 MMcfd.

Meanwhile, UMC told analysts earlier this year it would direct a majority of its domestic onshore capital spending toward the East Texas Cotton Valley reef play.

It said its interest averaged 40% in about 130,000 acres in East Texas along the trend. The company had identified well over 100 anomalies from 3D seismic data that could potentially be Cotton Valley reef prospects.

Cost of a completed well in the play is about $4 million. Copyright 1996 Oil & Gas Journal. All Rights Reserved.