Effects of biocide treatment and backflow pressure on the permeability of microbially fouled model cores

Sintered glass bead cores were plugged until the permeability was reduced to 1% or less of the original permeability by the injection of a slime-producing bacterium isolated from produced water. Scanning electron microscopy of fractured core sections showed that the bacteria were predominantly located in the uppermost sections, around the core inlet. Killing the bacterial cells in the plugging biofilm, using a biocide, had little effect on core permeability. The dead cells were only removed when backflow pressure, simulated by inversion of the test core followed by fluid injection, was applied and maintained at 55–69 kPa. Backflow of plugged cores containing live bacteria produced transient pressure-dependent increases in permeability that were proportional to the backflow pressure applied. We conclude that only sustained backflow procedures reduced permeability: such operations are not effective for oil recovery in field conditions.