The Effect of Bacteria on Sandstone Permeability

Detailed descriptions are given of materials, apparatus and the experimental procedure used to study the effect of bacteria on sandstone permeability. The factors affecting permeability during injection of bacterial suspensions which have been investigated are: - concentration of bacteria; - core permeability and median pore size; - species of bacteria, mode of aggregation and relative size; - injection rate or pressure differential; - mean pressure; and - depth of penetration of bacteria. The investigation demonstrated that bacteria cannot reduce core permeability to zero and that their effect on permeability is subject to definite limitations. Remedial or permeability restoration studies also were made. Acidization in combination with reverse flow was found to be an effective method for restoring permeability in cores partially plugged with bacteria. The relationship between the bacterial quantities in the laboratory tests and those found in field operations is discussed. The linear laboratory flow data have been translated into terms of field radial systems; these data indicate the most practical methods of maintaining injection rates in the presence of bacteria are to increase injection pressures or hydraulically fracture the formation. Introduction It has long been known that various bacteria flourish in the above-ground components of oil field water- injection systems. The presence of these bacteria has led to the suspicion that they might enter into the causes for reduction of injection well permeability, but only recently has an attempt been made to describe the effects quantitatively. Biocides are used in many cases without a firm knowledge as to whether the bacteria are killed, or if they are, whether the dead cells affect formation permeability. This project was undertaken as part of a study to determine the effect of bacteria, residual oil and precipitated solids such as iron sulfide or calcium carbonate on the permeability of sandstones and to learn whether any of these materials adversely affect brine injectivity in secondary recovery or disposal operations. This report deals with that portion relating to the effect of bacteria.