Buried in the rate request that Illinois regulators cut last month from nearly $129 million to $73 million is the final phase of Ameren’s modernization efforts for its natural gas storage field just south of Freeburg.

Since 2019, the utility company has been working toward transitioning seven of its 12 reservoirs, where Ameren stores billions of cubic feet of natural gas to be used in the colder months, from what’s known as vertical drilling to horizontal drilling.

This type of storage field requires a specific set of geological factors — mainly sandstone. Because the rock is so porous, Ameren can pump natural gas down hundreds of feet to be absorbed and stored.

Ameren borrowed the idea for horizontal drilling from natural gas production. Instead of just drilling vertically hundreds

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