Abstract: A secondary recovery and pipe cleaning operation for expended wells such as petroleum bearing wells containing hardened residual deposits and trapped liquids wherein a sonic generator is placed within the liquid in the reservoir being drilled or in a liquid level in the well pipe, and sonic energy generated thereby is transmitted through the liquid to create new fissures or break up tars and produce the formation or clean deposits from the well pipe. Liquid such as diesel oil can be added to the formation prior to sonic stimulation where insufficient liquid is present to carry the sonic energy throughout the formation or in the well pipe. Also, the sonic generator is movable within the formation and can be self-propelled.