Methods of controlling clay swelling and stabilizing subterranean geological formations containing swellable clays (e.g., montmorillonite, bentonite) are described. The methods involve treating the swellable clays with a composition containing an amidoamine-based gemini surfactant. The gemini surfactant has dual chains connected via an alkylene linker, whereby each chain contains a quaternary ammonium head group and an ethoxylated alkyl tail. As examined by linear swelling and free swelling tests, use of the gemini surfactant is effective in reducing swelling of the clays.