Petroleum Microbiology

Petroleum microbiology is a branch of microbiology that is concerned with the activity of microorganisms in the formation, recovery, and uses of petroleum. Petroleum is broadly considered to encompass both oil and natural gas. The microorganisms of concern are bacteria and fungi.

Much of the experimental underpinnings of petroleum microbiology are a result of the pioneering work of Claude ZoBell. Beginning in the 1930s and extending through the late 1970s, ZoBell's research established that bacteria are important in a number of petroleum related processes.

Bacterial degradation can consume organic compounds in the ground, which is a prerequisite to the formation of petroleum.

Some bacteria can be used to improve the recovery of petroleum. For example, experiments have shown that starved bacteria, which become very small, can be pumped down into an oil field, and then resuscitated. The resuscitated bacteria plug up the very porous areas of the oil field. When water is subsequently pumped down into the field, the water will be forced to penetrate into less porous areas, and can push oil from those regions out into spaces where the oil can be pumped to the surface.

Alternatively, the flow of oil can be promoted by the use of chemicals that are known as surfactants. A variety of bacteria produce surfactants, which act to reduce the surface tension of oil-water mixtures, leading to the easier movement of the more viscous oil portion.

In a reverse application, extra-bacterial polymers, such as glycocalyx and xanthan gum, have been used to make water more gel-like. When this gel is injected down into an oil formation, the gel pushes the oil ahead of it.

A third area of bacterial involvement involves the modification of petroleum hydrocarbons, either before or after collection of the petroleum. Finally, bacteria have proved very useful in the remediation of sites that are contaminated with petroleum or petroleum by-products.

The bioremediation aspect of petroleum microbiology has grown in importance in the latter decades of the twentieth century. In the 1980s, the massive spill of unprocessed (crude) oil off the coast of Alaska from the tanker Exxon Valdez demonstrated the usefulness of bacteria in the degradation of oil that was contaminating both seawater and land. Since then, researchers have identified many species of bacteria and fungi that are capable of utilizing the hydrocarbon compounds that comprise oil. The hydrocarbons can be broken down by bacteria to yield carbon dioxide and water. Furthermore, the bacteria often act as a consortium, with the degradation waste products generated by one microorganism being used as a food source by another bacterium, and so on.

A vibrant industry has been spawned around the use of bacteria as petroleum remediation agents and enhancers of oil recovery. The use of bacteria involves more than just applying an unspecified bacterial population to the spill or the oil field. Rather, the bacterial population that will be effective depends on factors, including the nature of the contaminant, pH, temperature, and even the size of the spaces between the rocks (i.e., permeability) in the oil field. Not all petroleum microbiology is concerned with the beneficial aspects of microorganisms. Bacteria such as Desulfovibrio hydrocarbonoclasticus utilize sulfate in the generation of energy. While originally proposed as a means of improving the recovery of oil, the activity of such sulfate reducing bacteria (SRBs) actually causes the formation of acidic compounds that "sour" the petroleum formation. SRBs can also contribute to dissolution of pipeline linings that lead to the burst pipelines, and plug the spaces in the rock through which the oil normally would flow on its way to the surface. The growth of bacteria in oil pipelines is such as problem that the lines must regularly scoured clean in a process that is termed "pigging," in order to prevent pipeline blowouts. Indeed, the formation of acid-generating adherent populations of bacteria has been shown to be capable of dissolving through a steel pipeline up to 0.5 in (1.3 cm) thick within a year.

See also Biodegradable substances; Economic uses and benefits of microorganisms