Gas, liquids flow rates hefty at Galveston Bay discovery

G. Alan Petzet
Exploration Editor

Extended flow tests indicate a large Vicksburg (Oligocene) gas, condensate, and oil field is about to be developed in western Galveston Bay.

Internal estimates indicate that ultimate recovery from the fault block in which the discovery well was drilled could exceed 1 tcf of gas equivalent of proved, possible, and probable reserves, said TransTexas Gas Corp. and Davis Petroleum Corp., both of Houston. The company estimates take into account 4 days of extended flow tests and a reservoir limits test. That test did not establish reservoir limits.

The field, in 7-10 ft of water 1 mile off San Leon about halfway between Houston and Galveston, is named Eagle Point.

The internal estimates are more than double a consulting engineer's estimate of 448 bcfe that was based on electric log interpretation in late 1997 of the discovery well, 1 State Tract 331. That estimate, by Netherland, Sewell & Associates, included proved, probable, and possible categories. The log indicated 161 ft of net pay in two zones with porosity up to 30%.

The well is in the Galveston County portion of the bay (see map, OGJ, Aug. 11, 1997, p. 75). The structure is in the "transition zone," out of reach of land seismic surveys and too close to shore to have been seen on bay surveys until recently.

Test program

The discovery well flowed at rates of 76.4 MMcfd of pipeline quality gas and 11,002 b/d of crude and condensate through a 48/64 in. choke with 7,600 psi flowing tubing pressure from Upper Vicksburg, consisting of 101 ft of net pay, at undisclosed depths. CAOF is 381 MMcfd.

The 1,300 BTU gas is expected to yield natural gas liquids at 146 bbl/MMcf.

TransTexas, the operator, did not test the lower, 60 ft pay zone because of mechanical difficulties encountered in the well. It plans to test the lower zone in the second well, 3 State Tract 331, which was drilling below 15,200 ft in early January. The No. 3 well is projected to 18,000 ft about 1/2 mile northeast of the discovery well.

The upper zone was one continuous pay section. The lower zone is more laminated and thinner bedded but is believed to hold significant volumes of gas, TransTexas said.

The two wells are expected to go on line by Mar. 31 at 50-75 MMcfd/well after a short 20 in. pipeline and gas processing plant are installed.

Eight wells are required to develop the fault block. Size of the greater field is not known.

TransTexas spudded the discovery well in late February 1997. Permitted to 18,000 ft, it encountered 9,600 psi surface pressure on May 6 while drilling at 15,400 ft in Vicksburg. It also cut significant hydrocarbon shows in shallower Frio sands not yet tested.

The company said pressure encountered by a nearby exploratory well drilled by Meridian Resource Corp., Houston, on a separate fault block is encouraging because it may extend the limits of the potentially productive horizons of the seismic feature and help establish the field's downdip limit. That well is the 1 State Tract 329, less than 2 miles northeast of the 1 S.T. 331.

Interests in Eagle Point are 75% for TransTexas and 25% for Davis, whose explorationists, landmen, and engineers developed and assembled drilling prospects in and around the bay.

More prospects

TransTexas and Davis control several prospects in the greater Galveston Bay area.

TransTexas was the successful bidder Jan. 6 for 1,488 acres on state tracts 308, 352, and 353, paying $1.3-2 million per tract. These are adjacent to the north, west, and southwest perimeters of Eagle Point field.

Elsewhere, initial wildcats on the Virginia Point and Goat Isle prospects are to reach TD within the month.

In Chambers County about 30 miles northeast of Eagle Point field, TransTexas's 1 Barrow Ranch flowed 29.2 MMcfd of gas and 334 b/d of condensate with 8,000 psi FTP. CAOF is 101 MMcfd. TransTexas was installing production equipment to handle 40 MMcfd.

The well logged Frio and Vicksburg pay on the flank of a salt feature adjacent to existing Elwood gas field.

Anhydrite formation limited Vicksburg production at the well, but delineation wells farther toward the structure's flanks are expected to contain thicker Vicksburg and Frio sections, TransTexas said.

The company was interpreting a 3D seismic survey of the area and spudded the first delineation well, 2 Barrow Ranch, in December. Davis is not involved in that prospect.