Breaking New Ground
Ameren Illinois literally had to go underground to perform “cosmetic surgery” on several of its natural gas storage fields, but the results are reshaping these 60-year-old-plus facilities.
The company is utilizing horizontal drilling in its shallow depleted reservoirs in Tilden, Freeburg, Eden and Centralia—an approach that’s proving to be both technically innovative and economically transformative.
The concept of horizontal drilling for storage fields first surfaced at Ameren Illinois around 2016. While a few other storage operators had experimented with it, Ameren Illinois faced a challenge: Fifty-one wells in Tilden and 81 wells in Freeburg were scattered across acres of farmland and, in the case of Tilden, even in residential backyards. Replacing each vertical well individually was cost-prohibitive and operationally complex.
Horizontal drilling offered an alternative: Drill six to seven wells from a single pad, extending laterally up to half a mile, and eliminate the need for extensive surface infrastructure. “We are going from 81 wells scattered throughout cornfields to three pads with six wells each—our footprint at Freeburg dropped from 4,600 acres to about 10 acres,” said Tim Eggers, director of storage fields for Ameren Illinois. “It’s a tremendous plus in reducing our footprint and derisking our operation.”
He added, “Most important is that our three-year, $40 million investment will allow the Freeburg Natural Gas Storage Field to provide the region with reliable, price-hedged gas supply for generations to come.”
These are the shallowest horizontal wells successfully drilled in the U.S., requiring a 300-foot vertical drill before turning 90 degrees, followed by a 2,500-foot horizontal section. Thanks to lessons learned while drilling the first pad, the company’s teams completed the second pad in just 55 of the scheduled 75 days. The final pad is planned for 2026, pending regulatory approval.
While most people conceive of reservoirs containing oil, sitting 10,000 feet deep, Ameren Illinois’ storage fields sit at 850 feet in Tilden and at just 350 feet in Freeburg. This posed a significant technical hurdle. Without the weight of a long string of heavy drill pipe to provide force to make the curve, engineers had to rely entirely on motor-driven force to guide the drill bit.
“Most people didn’t think it was possible,” said Eggers. “You’re dealing with a seven-inch diameter steel pipe and making a 90-degree turn only 350 feet below the surface into a sandstone seam that’s just 20 feet thick. That is really challenging.”
A successful test well at Tilden in 2019 initiated a multi-year transformation. By 2021, Ameren Illinois replaced Tilden’s 51 wells with nine horizontal wells. Freeburg’s 81 wells are being replaced with 18 horizontal wells between 2024 and 2026, reducing 16 miles of pipeline to just two miles of new steel. In addition, Freeburg’s 4,600-acre spread will now be concentrated into just 10 acres across three protected well pads.
The outcome: safety, efficiency and environmental wins. Retired pipelines are purged, foamed, and plugged, remaining safely in place. This eliminates the need for annual pigging, corrosion monitoring and other maintenance across 26 miles of small-diameter pipe. The shift also dramatically reduces third-party damage risk—no more wells in backyards or crop fields, and fewer chances of farm equipment strikes or crop damage. Maintenance is streamlined, and landowner compensation is also no longer a recurring concern.
While the geology of the fields remains unchanged, horizontal wells provide greater contact with the reservoir, enabling higher withdrawal and injection rates. This boosts daily and hourly throughput, enhancing flexibility and responsiveness to demand—especially valuable in peak periods or future growth scenarios.
Ameren Illinois’ horizontal drilling initiative could be considered a blueprint for modernizing natural gas storage. “These are just good projects where you’re investing dollars, decreasing your risk, and lowering ongoing operating costs,” said Brad Kloeppel, senior director of gas operations for Ameren Illinois. “The engineers love it because it’s really cool engineering. The accountants love it because we’re going to save half a million dollars in O&M on an ongoing basis.”