a microbial system is provided for selective plugging of permeable regions of a subterranean formation , for use in conjunction with injection of surfactant - containing foams . bacteria indigenous to the target formation are isolated , and selected for ability to degrade the surfactant of interest . small , non - adherent ultramicrobacteria , or umb , are prepared from the selected culture by starvation . the umb and the surfactant - containing foam are then injected into the target formation . the surfactant allows the foam to penetrate into the formation . the umb then revive to their vegetative state , degrade the surfactant and produce exopolymer , thus plugging the formation .