Investigation into the impact of biosurfactant in heavy oil reservoirs

Ukwungwu, SV

Abstract

Exploitation of oil resources in mature reservoirs is essential for meeting future energy demands. Despite the primary and secondary oil recovery, significant amount of residual oil is still left behind in the reservoir, necessitating tertiary recovery methods. These typically includes surfactant flooding, polymer flooding, Microbial Enhanced Oil Recovery (MEOR) etc. To exemplify the potential of microorganisms to degrade heavy crude oil to reduce its viscosity, is part of a process known as MEOR. In recent times surfactants produced by microbes have gained wider acceptability in the petroleum industry due to their low toxicity and ease with which they are naturally broken down in the environment. Petrochemical-based synthetic surfactants are currently used in substantial amounts to increase recovery of hydrocarbons, and these surfactants are more recalcitrant in the environment.

The present study therefore, uses a technique to utilise microbes that will economically achieve a scale of Enhanced Oil Recovery (EOR) through biosurfactant production, lowering of interfacial tension (IFT) and contact angle, changes in rock wettability of sandstone grains and biosurfactant flooding. Three biosurfactants were produced under laboratory conditions, from three species of the genus bacillus using sucrose 3% (w/v) as their carbon source for growth and metabolism. These species produced biosurfactants of different specific activities that resulted in different impacts on IFT and contact angle. The biosurfactants produced are BS-1, BS-2 & BS-3. After applying the cell-free extracellular biosurfactants to the system, the results show that there is reduction in interfacial tension from 56.95 mN/m to 4.49 mN/m, 6.69 mN/m, and 10.94 mN/m. Also, the contact angle of the oil film was significantly reduced from 147.04° to 111.84°, when the cell-free extracellular biosurfactant (BS-2) was applied to the system.

Qualitative wettability tests were also performed on the sandstone crushed rock samples, which shows that, the spent culture medium changes wettability of the grains to water-wet and intermediate-wet. It should be noted that the decomposition property of sucrose as a carbon source makes it eco-friendly for biosurfactant production. The biosurfactant flooding also found to have a recovery of 38% (an interval of nominally 8%) against 30% water flooding, due to the development of a water-wet state, which was achieved by flooding the core with 5PV of BS-2 supernatant solution.

Economic analysis was also considered in determining the possible profitability of the corresponding MEOR method with addition of biosurfactant costs that were utilised during this study. The case study results of these analysis show that the cumulative cashflow, indicated a payback period of 2.54 years for a capital investment of $45.32 million, given a typical oil production of 2,720 barrel per day. Moreover, with this type of biosurfactant (BS-2) supernatant, it has become evident that there can be an enhance recovery in the heavy oil reservoir by changing the wettability of rock grains. This thus, provides new tools for use in EOR schemes that leads to promising environmental sustainability.

• Thesis Type: Thesis
• Acceptance Date: Oct 1, 2017
• Deposit Date: Feb 26, 2018
• Publicly Available Date: Feb 26, 2018