A previously watered-out and abandoned gas reservoir in the Sub-Clarksville formation of the Mt. Selman field in North East Texas was reentered and secondary gas recovery initiated by pumping of water. Pumping was done with a sucker rod pump and bottom hole pressures in the producing well and a nearby observation well was measured via gas filled capillary size tube extending into open ended larger tubing downhole. Numerical modeling to match past performance and project possible future production was done before and during the field test to compare theoretical and actual production results. A series of draw-down and build up tests over a three month period were performed to evaluate the reservoir and determine its potential for secondary gas recovery. No residual gas cap of mobile free gas was found. The remaining free gas was apparently trapped as an immobile dispersed phase within the reservoir rock matrix. The amount of gas dissolved in the reservoir brine was about 7 Scf/Stb (1.28 std m3/m3). The produced gas/brine ratio varied from 7 to 25 Scf/Stb (1.28 std m3/m3 - 4.5 std m3/m3) indicating that some immobile gas was mobolized by pumping water to lower the reservoir pressure. Gas analysis has shown the trapped free gas to be richer in heavier hydrocarbons than the dissolved gas.

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