Page 449 - Fundamentals of Enhanced Oil and Gas Recovery

Microbial Enhanced Oil Recovery: Microbiology and Fundamentals 437

10.11.8 Surface and Interfacial Tension Alteration
Reducing the surface tension between the oil and water increase the yield of flood
recovery [31]. Surfactants are the chemicals incorporated to do this. The features deter-
mining the most optimum biosurfactant are strong facial activity, a low CMC, good sol-
ubility, adequate tolerance to pH and temperature, and high emulsion capacities [798].
Further details about surface and IFT alteration are provided in Section 10.10.1.

10.11.9 Repressurizing the Reservoir
Re-pressurization of the reservoir is a traditional enhanced oil recovery method [799].
Applying more pressure can force the remained oil out of the pores [23,700].
Microorganisms can produce gases in situ to repressurize the reservoir and subse-
quently promote gas drive. Bacteria can produce gases such as methane, hydrogen,
and carbon dioxide through fermenting the carbohydrates [15].N 2 , which is pro-
duced by NRB, can increase the reservoir pressure too [18]. These metabolic gases
can enhance the oil recovery by increasing the reservoir pressure. Further details can
be found in Section 10.10.5.

10.11.10 Oil Swelling
Biogenic gases can be dissolved in the oil to increase it volume and therefore decrease
its density. This process referred to as oil swelling ease the oil displacement [66].
Further details can be found in Section 10.10.5.

10.11.11 Well Stimulation via Removing the Wellbore Damages
During this process, the barriers such as paraffin and asphaltene deposits will be
removed from the well bore. However, this process only increases the productivity
index and accelerates the recovery. In other words, it makes no increase in the amount
of produced oil [23]. In addition, the biologically produced acids, solvents, and gases
can remove the debris and scales in the injection well so that the injectivity increases
[6]. Although this is not an EOR process, such processes extend the life of a field by
reducing the operating costs or enhancing the daily revenue for several cases [11,800].
There are several studies reporting successful microbial paraffin removal processes from
individual wells [81,691,801,802]. Further details can be found in Section 10.11.1.

10.12 MEOR CONSTRAINTS AND SCREENING CRITERIA

One of the most important aspects of MEOR is the screening of the reservoir
physical properties, which are greatly effective on the capability of the microorganisms