The exploration, production, and environmental biotechnology of petroleum are all topics covered in the Journal of Petroleum & Environmental Biotechnology. Petroleum exploration and production involves extracting hydrocarbons from the earth's underground reservoirs with the aid of several different disciplines, including petroleum geology, drilling, reservoir simulation, reservoir engineering, completions, and oil and gas facilities engineering. Crude oil or natural gas are two of the available forms of the hydrocarbons that were generated. Environmental engineering is a method for integrating science and engineering that can be used to enhance the quality of the environment, including the air, water, and land.

The principal idea of this method was to inject or encourage indigenous bacteria to produce CO2and/or methane to help re-pressurize the reservoir, decrease oil viscosity and, in the case of limestone or carbonaceous sandstone, to leach out calcite and siderite thus liberating adsorbed oil. Behlülgil et al. (1992) injected the anaerobic bacterium Clostridium acetobutylicum into a 1D model reservoir of limestone grains with a shut-in period of approximately 45 h, and found an overall increase of 12% in MEOR effectiveness, compared to con-trols. This increase was attributed to a reduction in viscosity of Raman crude oil from 1096 to 843 ± 86 cP and an increase in ph. The authors also observed that a doubling in shut-in period resulted in no additional oil recovery compared to 45 h while, interestingly, the oil viscosity increased 31%, and pH decreased (moreacidic than control). While the authors had no explanation for this phenomenon at that times it is suggested that C.acetobutylicum started to produce organic acids which dissolved part of the lime-stone thus releasing the heavier fractions of the crude oil. Ten years later, the same authors showed that the reduction in Garzan crude oil viscosity from 80 cP to 50 cP was mainly due to dissolved CO2produced by C. acetobutylicum. The stimulation of methane production for oil recovery, however, should be treated with caution. Methane is not only ignitable but also a potent greenhouse gas which may escape from shallow reservoirs into the atmosphere and affect global climate. Alternatively, nitrogen could also be produced using denitrifying bacteria.

Literature on CO2 flooding reconfirmed that CO2does lead to the dissolution of sandstone components under field conditions. The question, however, whether bacteria are able to produce sufficient amounts of CO2in a naturally anaerobic environment to achieve similar effects, remains to be answered. A minimum miscibility pressure may also be required to notice EOR. In addition, field experience has shown that HCO3^- concentration increased in the aqueous phase, resulting in a drop in pH and CaCO3scaling problems at the production well, where pressure and acidity of the solution is decreased (Goodyear et al., 2003). Furthermore, relative low pressure zones in the reservoir will allow compressedCO2to expand thus cooling the surroundings. This may, depending on temperature and pressure, cause the precipitation of the paraffin/asphalting fraction with detrimental effect on oil recovery. Another issue of concern is the complexity involved in using CO2for (M)EOR. Up to 5 phases can co-exist in a CO2flood, whichcomplicates the understanding, modeling and prediction of ex-pected oil recovery:

Aqueous phase

Liquid hydrocarbon phase

Liquid CO2phase

Gaseous CO2phase

Solid asphaltene (precipitate) phase