Abstract
Microbial Enhanced Oil Recovery (MEOR) is one of the tertiary recovery methods. The high viscosity and low flow characteristics of heavy oil makes it difficult for the extraction from oil reservoirs. Many spore-forming bacteria were isolated from Oman oil fields, which can biotransform heavy crude oil by changing its viscosity by converting heavier components into lighter ones. Two of the isolates, Bacillus firmus BG4 and Bacillus halodurans BG5, which showed maximum growth in higher concentrations of heavy crude oil were selected for the study. Gas chromatography analysis of the heavy crude oil treated with the isolates for nine days showed 81.4% biotransformation for B. firmus and 81.9% for B. halodurans. In both cases, it was found that the aromatic components in the heavy crude oil were utilized by the isolates, converting them to aliphatic species. Core flooding experiments conducted at 50 °C, mimicking reservoir conditions to prove the efficiency of the isolates in MEOR, resulted in 10.4% and 7.7% for B. firmus and B. halodurans, respectively, after the nine-day shut-in period. These investigations demonstrated the potential of B. firmus BG4 and B. halodurans BG5 as an environmentally attractive approach for heavy oil recovery.
Highlights
Global energy requirements demand an increased production of crude oil
The mineral compositions of the 10 soil samples measured by X-ray diffraction (XRD) showed that all of the soil samples contained calcite and quartz; albite and palygorskite were present in 8 soil samples out of 10 samples tested
This study showed that isolates, B. firmus and B. halodurans were mostly utilizing aromatic fractions in the crude oil and fractionation of which led to increase in the amount of aliphatic compounds
Summary
Global energy requirements demand an increased production of crude oil. During conventional recovery methods, about 30–40% of crude oil is recovered while rest remains trapped in the reservoir [1,2,3,4]. Crude oil is a fossil fuel which is considered as non-renewable energy source. It is composed of a mixture of different hydrocarbons (including alkanes/paraffins, alkenes/olefins, cycloalkanes/naphthenes, and aromatics), complex hydrocarbons (such as polycyclic aromatic hydrocarbons), resins, asphaltenes, along with certain other hetero-species, containing nitrogen, oxygen and sulfur [5]. Current methods of extraction include open-pit mining, steam stimulation, the addition of sand to the oil, and the injection of air into well to create subterranean fires that burn heavier hydrocarbons to generate heat. Transportation of these types of crude oil through pipelines poses much difficulty and requires certain diluting agents. This will result in contamination of the light crude and a reduction in its value [6]
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