Microbial enhanced heavy crude oil recovery through biodegradation using bacterial isolates from an Omani oil field

Abstract

Background: Biodegradation is a cheap and environmentally friendly process that could breakdown and utilizes heavy crude oil (HCO) resources. Numerous bacteria are able to grow using hydrocarbons as a carbon source; however, bacteria that are able to grow using HCO hydrocarbons are limited. In this study, HCO degrading bacteria were isolated from an Omani heavy crude oil field. They were then identified and assessed for their biodegradation and biotransformation abilities under aerobic and anaerobic conditions.

Results: Bacteria were grown in five different minimum salts media. The isolates were identified by MALDI biotyper and 16S rRNA sequencing. The nucleotide sequences were submitted to GenBank (NCBI) database. The bacteria were identified as Bacillus subtilis and B. licheniformis. To assess microbial growth and biodegradation of HCO by well-assay on agar plates, samples were collected at different intervals. The HCO biodegradation and biotransformation were determined using GC-FID, which showed direct correlation of microbial growth with an increased biotransformation of light hydrocarbons (C12 and C14). Among the isolates, B. licheniformis AS5 was the most efficient isolate in biodegradation and biotransformation of the HCO. Therefore, isolate AS5 was used for heavy crude oil recovery experiments, in core flooding experiments using Berea core plugs, where an additional 16 % of oil initially in place was recovered.

Conclusions: This is the first report from Oman for bacteria isolated from an oil field that were able to degrade and transform HCO to lighter components, illustrating the potential use in HCO recovery. The data suggested that biodegradation and biotransformation processes may lead to additional oil recovery from heavy oil fields, if bacteria are grown in suitable medium under optimum growth conditions.

Fig. 1

Phylogenetic analysis using maximum likelihood method for bacterial isolates AS1–AS15 [GenBank: KJ729814–KJ729828]

Fig. 2

The clearance zones during well-assays for 10 days, for all the isolates after a 20, b 50 and c 70 h. The bacterial strains AS1–AS10 were grown in medium M2, strains AS11–AS13 in medium M4 and strains AS14–AS15 in medium M5

Fig. 3

Bacterial growth assay (OD₆₆₀). The data represents average of three independent experiments with SD values (±). Three different miocrobial density trends were observed in the medium M2: high density (AS3, AS4 and AS5), intermediate density, initial higher density (AS1, AS2 and AS6) and low density (AS7–AS10). The media M4 and M5 showed poor growth

Fig. 4

GC-FID chromatograms of heavy crude oil degradation by B. licheniformis AS5 isolate

Fig. 5

The degradation of heavy crude oil by isolates AS1–AS10 under aerobic conditions. More than 50 % of the C24 was degraded. C12 and C14 increase by several isolates indicated HCO biotransformation from heavier to lighter compounds

Fig. 6

GC-FID chromatograms (a, b) of heavy crude oil degradation by isolates AS2 and AS5, under anaerobic conditions

Fig. 7

Cumulative recovery factor versus injected PV using B. licheniformis AS5 isolate. WF recovered = 24.2 % of OIIP, BNF = 2.5 % of OIIP recovered. WF after 5 days of incubation of isolate B. licheniformis AS5 resulted in an additional 16 % recovery

Fig. 8

Chromatograms of heavy crude oil recovered from the initial water flood and from the water flood after microbial treatment

Fig. 9

a SEM image of Berea core-plug at sterile conditions (control). b SEM image of the growth of B. licheniformis AS5 isolate in Berea core-plug after core-flooding experiment at 100,000 magnification, leading to additional heavy crude oil recovery

Fig. 10

Schematic summary of the procedures followed for isolation, identification and screening of heavy crude oil degrading bacterial isolates