The potential of indigenous Paenibacillus ehimensis BS1 for recovering heavy crude oil by biotransformation to light fractions.

Biji Shibulal,Abdulkadir E. Elshafie,Ali S. Al-Bemani,Saif N. Al-Bahry,Yahya M. Al-Wahaibi,Sanket J. Joshi,Pankaj Kumar Arora

doi:10.1371/journal.pone.0171432

Abstract

Microbial Enhanced Oil Recovery (MEOR) is a potential technology for residual heavy oil recovery. Many heavy oil fields in Oman and elsewhere have difficulty in crude oil recovery because it is expensive due to its high viscosity. Indigenous microbes are capable of improving the fluidity of heavy oil, by changing its high viscosity and producing lighter oil fractions. Many spore-forming bacteria were isolated from soil samples collected from oil fields in Oman. Among the isolates, an autochthonous spore-forming bacterium was found to enhance heavy oil recovery, which was identified by 16S rDNA sequencing as Paenibacillus ehimensis BS1. The isolate showed maximum growth at high heavy oil concentrations within four days of incubation. Biotransformation of heavy crude oil to light aliphatic and aromatic compounds and its potential in EOR was analyzed under aerobic and anaerobic reservoir conditions. The isolates were grown aerobically in Bushnell-Haas medium with 1% (w/v) heavy crude oil. The crude oil analyzed by GC-MS showed a significant biotransformation from the ninth day of incubation under aerobic conditions. The total biotransformation of heavy crude oil was 67.1% with 45.9% in aliphatic and 85.3% in aromatic fractions. Core flooding experiments were carried out by injecting the isolates in brine supplemented with Bushnell-Haas medium into Berea sandstone cores and were incubated for twelve days under oil reservoir conditions (50°C). The extra recovered oil was analyzed by GC-MS. The residual oil recovered from core flood experiments ranged between 10–13% compared to the control experiment. The GC-MS analyses of the extra recovered oil showed 38.99% biotransformation of heavy to light oil. The results also indicated the presence of 22.9% extra aliphatic compounds in the residual crude oil recovered compared to that of a control. The most abundant compound in the extra recovered crude oil was identified as 1-bromoeicosane. The investigations showed the potential of P. ehimensis BS1 in MEOR technology by the biotransformation of heavy to lighter crude oil under aerobic and reservoir conditions. Heavy oil recovery and biotransformation to lighter components are of great economic value and a few studies have been done.

Highlights

Crude oil is a main source of energy worldwide, which is economically important
The intent of this study is to demonstrate the potential of Paenibacillus ehimensis strain BS1 in the biotransformation of heavy crude oil (American Petroleum Institute, API = 4.57 ̊) for Microbial Enhanced Oil Recovery (MEOR) using wet lab incubation method and core flood method
The isolate was identified by MALDI biotyper as Paenibacillus genus and by 16S rDNA sequencing; the nucleotide sequence was submitted in NCBI GenBank as Paenibacillus ehimensis BS1, Accession No KP119106.1

Summary

Introduction

Crude oil is a main source of energy worldwide, which is economically important. Due to increase in energy demands and maturity of oil fields, alternative technologies should be implemented.Heavy crude oils are called “Unconventional crude oils” because of their high viscosity and density reaching near or even greater than that of water. Resins, nitrogen and sulfur containing heteroaromatics and several metals, nickel and vanadium are present in them. They are so called because they cannot be produced, transported or refined by conventional methods [1,2,3,4]. Heavy crude oil reserves are more than seven times larger than conventional oil reserves. The largest of these are in the Orinoco Oil Belt of Venezuela. Since there is depletion of conventional crude oil, in order to meet the energy demands, there is a great demand for heavy crude oil [5,6,7]

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