Lafayette-based Stone Energy Corp. plans to sell 5 million shares of stock and use the proceeds for general corporate purposes that include developing a deepwater natural gas discovery in the Gulf of Mexico known as the Amethyst prospect.

At Wednesday’s closing price, Stone would generate $221.5 million before expenses.

In February, Stone said the Amethyst prospect had a reservoir of recoverable natural gas 90 feet thick. The reservoir has an estimated yield of 60 to 80 barrels of natural gas liquids per million cubic feet of natural gas.

Stone said it might also drill a second well in its Cardona South lease, also in the deepwater Gulf; a potential Utica Shale development, a natural gas formation in the Northeast; and acquire additional acreage in the Appalachians.

Stone is also giving underwriters a 30-day option to buy 750,000 additional shares in case investors buy more than 5 million shares. The additional shares could generate $33.2 million before expenses.