Abstract
This paper presents the results of a reservoir simulation study of the Sciota aquifer gas storage field in McDonough County, Illinois. The field has been in operation since the early 1970's and is currently operating with 12 injection wells and five observation wells. The field is operated by the Central Illinois Public Service Company, now part of AmerenCIPS.
The objectives of this study were to (1) build a computer database of all historical pressure and injection/withdrawal data, (2) determine inventory volumes over time, (3) determine the cause of the low working-gas to base-gas ratio, and (4) determine if field deliverability could be improved.
In this study, weekly injection/withdrawal data and daily wellhead pressure data were first computerized and analyzed to evaluate past reservoir performance. Analysis of the injection/withdrawal data indicated a cumulative net gas injection of about 4.7 Bscf from November 1972 to July 1997. However, the average working gas was only about 0.3 Bscf for the last nine storage cycles, giving a working-gas to base-gas ratio of only about 6.4 %.
Analysis of the wellhead pressure data indicated that the wells were loading up with water during each withdrawal period. Using all available reservoir and geology data, we constructed a two-phase gas-water model of the Sciota storage pool and history matched the injection/withdrawal on a monthly basis from 1972 to 1997. We determined that the working gas could possibly be increased threefold from 0.3 Bscf to 1 Bscf by maintaining lower bottomhole pressures during withdrawal.
