Abstract

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 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 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 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.

Introduction

The test of secondary gas recovery by co-production of gas and water from the Mt. Selman, Texas field was a joint effort by Lexington Gas and Marine, Secondary Gas Recovery Incorporated and the Gas Research

Institute (GRI). Lexington was the operator and GRI conducted the technical program to obtain and analyze production program to obtain and analyze production test data. The Institute of Gas Technology performed the R and D field operations. Eaton Operating Company performed evaluation of the project and performed evaluation of the project and contract management of the field work for GRI.

The field had been abandoned for about 12 years before this current test. The wells had watered-out under primary production but there was reason to believe that significant quantities of gas still remained in the reservoir when the primary production was terminated. The basic production was terminated. The basic concept for the project was to reenter the old wells and reinstitute production of gas and water to determine if adequate volumes of gas could be co-produced with the water for the field to again be commercially profitable. Other projects for secondary gas recovery from watered-out reservoirs have been reported by Exxon (Ref. 1–3).

To further evaluate potential secondary gas recovery by co-production of water a field test program was developed for the Mt. Selman field. This research project provided an in-depth analysis of the provided an in-depth analysis of the production from the Mt. Selman field and production from the Mt. Selman field and some further knowledge on the general aspects of the technology of co-production. GRI funded the research aspect of the test as part of the GRI Unconventional Natural Gas Program to address selected technical problems of interest to the gas producing industry which will have an impact on developing additional gas supply by co-production techniques (Ref. 4). This paper is a preliminary summary of the test and preliminary summary of the test and results. More detailed information about the test and results will be available in other reports.

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