# A Novel Approach to Enhance Crude Oil Recovery Ratio Using Selected Bacterial Species
## 4 Discussions
### Transformation of Hydrocarbon  
The GC analysis showed that heavy oil that is trapped in an oil reservoir after primary and secondary recovery can be recovered by biotransforming the heavier fractions to lighter ones. The results have demonstrated that not all the alkanes were equally reduced as a difference was recorded (Figures 3 and 4). Comparing these results with other reports, the _Bacillus_ species isolated from a natural environment had the ability to degrade the heavy fraction of crude oil and change the chemical and physical properties of Bouri crude oil. Close strains such as _B. firmus_ and _B. halodurans_ were shown to result in the fractionation of higher \(n\)-alkanes with carbon numbers up to C54 [1]. The microbial degradation of oil and biosurfactants production are major factors taking place during microbial water injection, microbial activities, and interactions of metabolic products with oil and cores contributing to the enhancement of oil recovery [25,26]. The addition of _Thermoanerobacter brockii_ subsp. _Lactiethylicus_ 9801T was reported to degrade alkanes and produce important metabolites such as biosurfactants and gases which positively contribute to the oil recovery process [27]. The percentage of heavier and lighter hydrocarbons was reduced to 77 and 63%, respectively, during the period of incubation (55 \({}^{\circ}\)C) with _Bacillus_ species, and 66% on heavier fractions of Bouri crude oil at 37 \({}^{\circ}\)C.  
_Pseudomonas putida_ and _Nocardiia cyriacigeorgica_ have decreased the concentration of heavier hydrocarbons C22+, to 61% at 55 \({}^{\circ}\)C. On the other hand, a slight decrease in lighter hydrocarbons of 45% and 16%, respectively, was recorded for both species at 37 \({}^{\circ}\)C. The crude oil utilization capability and degradation potential of both _Pseudomonas_ and _Bacillus_ sp. were reported in previous studies [28,29]. The heavy crude oil biodegradation and biotransformation were evident by the decrease in lighter and heavier compounds. Bacterial strains were found to destroy heavier fractions which led to an increased API of crude and tended to reduce viscosity, thus increasing the oil's mobility and flow characteristics. Moreover, the degradation of alkanes was also very significant, probably from the effect of biosurfactants production (data not shown). These findings suggest that the bacterial strains used may be potential candidates for the biotransformation of heavy crude oil. The isolated bacteria strains (_Pseudomonas putida_, _Bacillus_ species, and _Nocardiia cyriacigeorgica_) significantly decreased the oil viscosity from 22.47 Pa.s at 0.8481 s\({}^{-1}\) to 4.127 Pa.s at 98.73 s\({}^{-1}\). According to [30], using microbes for biodegradation long chain paraffins may have the following benefits: the amount of paraffin will be reduced, resulting in reduced paraffin precipitation or deposition problems along the production flow line, and as a result the viscosity of crude oil will be reduced, increasing its API gravity. The microbial degradation of crude oil results in its dissolution away from the block and eventually being carried out in porous media while simultaneously resulting in the phenomenon of swept volume expansion that remarkably improves the oil displacement effect [31]. The isolates were shown to be feasible for similar applications in a number of laboratory experiments reported before. However, they have not been widely used in heavy oil-saturated dolomite sandstone cores before and, since rock properties, such as mineral content, grain and pore size, porosity, permeability, under some physical and chemical conditions that resemble those experienced in an oil production reservoir can vary, such as high salinities and temperatures, this study highlights the novelty of using these strains,_Bacillus_ species, _Pseudomonas putida_ and _Nocardia cyiacigeorgica_, as excellent candidates that can reduce oil viscosity, leading to some biotransformation and an increase in oil recovery. _N.