A three-dimensional (3-D) reservoir model, developed from stratigraphic and petrophysical data, was used to understand the past behavior of the Hillsboro Gas Storage Field and to investigate the field's performance under various future development. Twenty-two years of the gas storage reservoir history, comprising the initial gas bubble development and seasonal gas Injection and production cycles, were examined with a full-field, gas-water, reservoir simulation model. Key issues in storage developments examined after successful history matches of the past gas storage performance included (1) the maximum possible total gas-in-place volume without gas loss and (2) the optimum base load volume that permits the achievement of the peak-day rate requirements. The results from various simulated development strategies suggest that the gas-water front is already in the vicinity of the west observation well and that increasing the field's total gas-in-place volume would cause gas to migrate beyond the east, north and west observation wells. They also suggest that storage enlargement through gas injection into the lower layers may not prevent gas migration. Concerning gas deliverability, simulated results suggest that a peak day rate of about 150 Mmscf/D can be achieved with up to 80% of the working gas produced before the peak day and that the peak day rate would fall below 125 Mmscf/D when 85% or more of the working gas is produced before the peak day. Furthermore, the results suggest that the addition of strategically-located new wells would boost the simulated gas deliverabilities.
The Hillsboro Gas Storage Field project, which began in August 1973, covers over 4,000 surface acres (16.2 km2) and contained a total natural gas inventory of 21.7 bcf (614.5 × 103 m3) at the start of the 1994 withdrawal season. The working gas inventory estimate is 7.6 bcf (212.4 × 103 m3) or 35% of total gas in storage.
Owned and operated by the Illinois Power Company, the Hillsboro Field consists of an anticlinal dome (fig. 1) located in Montgomery County, Illinois, within the St. Peter Sandstone (fig. 2). The crest of the field lies at a subsea elevation of -2490 feet (-759 m). Fourteen (14) gas wells, four (4) water (observation) wells and four shallow wells provide the well controls and data for both the initial geologic modeling and interpretation, and the present reservoir simulation modeling. The primary objectives of this study include the following:
integrate a previously generated 3-D geologic model into a reservoir simulation model;