eld tests; a large amount of information may have been accumulated, but at present it is unavailable to the general public.
In the early 1940s, it was observed that bacteria could clog or plug a reservoir. Early studies relating to bacterial plugging of a reservoir were mainly concerned with the prevention of this process.
Kalish et al. (38) studied the effects of bacterial plugging in sandstone cores and determined that the slime-forming and larger bacteria have a much greater effect on permeability reduction than the smaller and non-slime-forming ones. Jang et al. (39) and Jenneman et al. (40) examined the effect of rock permeability on bacterial transport. Both concluded that nutrients such as dissolved sucrose, inorganic salts, and yeast extract move easily through porous media. Jang et al. demonstrated that bacterial spores, because of their size and cell surface properties, travel faster and with less adsorption to rock through sandstone cores than bacterial cells. Jenneman et al. reported that nutrients and bacterial cells are selectively transported to zones of high permeability.
It is clear that microbial movement should receive more attention. Other microbial technological processes used in the environment may help to further transport knowledge and research. Virtually no studies have been done to examine microbial migration under actual reservoir conditions of pressure, temperature, and field brine and oil. These studies are vital to our understanding of microbial transport for MEOR processes.
Because of the decreasing supply of petroleum and the increasing production costs, a potentially inexpensive method such as MEOR may prove useful and economical. However, MEOR has only recently undergone an overall examination of the available technology. This review indicates that many reservoir characteristics must be determined before applying MEOR. Some of these characteristics are porosity, permeability, salinity, temperature, and pressure. It is unlikely that a single MEOR method can be applied to all types of reservoirs.
Areas of MEOR research that merit more investigation are listed here.
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