This paper reviews microbial interactions with heavy oil and identifies promising areas for research and development of new biotechnology for facilitating the exploitation of heavy-oil resources.
Microbial degradation of heavy crudes occurs rapidly only where O2 is available. Biodegradation results in the preferential removal of simple alkanes and aromatics to yield a more viscous final crude that is close to a bitumen in its chemical composition. There is little evidence for the buildup of partially oxidized fractions in the crude.
Microbial growth on heavy oil is often accompanied by the emulsification of the oil because of the production of biosurfactants.
Although the use of soil microorganisms as an indicator for heavy oil is not likely to become an important exploration tool in North America, a number of heavy-oil applications hold some promise for future biotechnology. These include microbially enhanced oil recovery, flow diversion, and water control in situ through selective plugging, deemulsification of stubborn EOR production emulsions, organic sulfur removal, viscosity reduction for pipelining, and miscellaneous surfactant applications for cleaning purposes, cold-water oil sands separation, etc.
Figures & Tables
Exploration for Heavy Crude Oil and Natural Bitumen
Gross volumes of oil, which must be kept in mind to address the volume/size framework, may be thought of in order from largest to probably smallest volumes as follows: (1) generated; (2) dissipated; (3) degraded/ partially preserved; and (4) trapped and conventionally producible. Basic knowledge of these volumes may be from greatest to least in essentially reverse order.
The 332 largest known accumulations (less than 1% of the total number) account for more than three-quarters of the known 7.6 trillion bbl of oil and heavy oil or tar in more than 40,000 accumulations in the world. About 2.4 trillion bbl of estimated undiscovered conventional oil added to the known volume of 7.6 trillion bbl yields a total of 10 trillion bbl known or reasonably estimated. World-wide cumulative production of about 500 billion bbl of oil accounts for only 5% of the gross.
Oil in place must be estimated for conventional oil fields before comparison with heavy oil and tar accumulations. The size range of accumulations considered in the size distribution of the 332 largest known accumulations is from 0.8 to 1850 billion bbl of oil. The smallest conventional fields in the distribution are about 1 billion bbl because the size cut-off is 0.5 billion bbl of oil recoverable. The size distribution of the 332 largest known accumulations approaches log normal and is overwhelmed by the largest three supergiant tar deposits that hold nearly half of the total 5495 billion bbl.
Globally, the largest three accumulations, all heavy oil or tar, are in South and North America; the two largest conventional oil fields are in the Middle East. Prudhoe Bay and East Texas fields rank 18 and 34, respectively, in descending size order.