One of the known causes of formation damage in producing wells is through the plugging of the formation by microorganisms. The result of the formation plugging will be a reduction in permeability. There is no effective means to date that can effectively deal with this type of formation damage, which can occur during drilling, completion, or secondary recovery operations. The biocide treatment used in waterflood operations is only effective in killing the microorganisms that are in the water prior to pumping it down the hole, but it will not be effective as far as the future growth of the microorganisms is concerned in the formation. A series of experiments were conducted using cores of Berea sandstone. The permeabilities of the cores were determined after preparation. The cores were then injected with micrococcus luteus bacteria at several different pressures. The permeabilities of the cores were determined again by the same technique under the same conditions. A 50% to 75% decrease in permeability was resulted from bacterial injection (depending on whether the core was cut horizontally or vertically along the formation bedding plane). The cores were examined with a scanning electron microscope (SEM). The SEM study showed that the pore sizes ranging from 0.4 to 10 microns were seriously plugged by the microorganisms. The damage was minimal for the pores larger than 50 microns. The cores were then injected with various volumes of a 2% concentration of oxidizers at several different pressures. The two oxidizers used were sodium hypochlorite and potassium hypochlorite. The results of flushing the cores with an oxidizer was partial restoration of the original permeability. Depending on the core sample, the permeability of the damaged cores was improved by 3% to 25% for the rate of treatment in the study. In the last phase of the study, corrosion tests were conducted. The results of the corrosion test showed that for the same time of exposure of corrosion coupons to the oxidizers, the amount of corrosion was found to be higher than the amount of corrosion for a drilling or some packer fluids. The exposure time of an oxidizer in a field application will be much less than the exposure time of drilling or packer fluids, and therefore, the corrosion for the oxidizer can be considered as insignificant.

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