Microbial Enhanced Oil Recovery (MEOR)

Microbial Enhanced Oil Recovery (MEOR)

MEOR involves processes responsible for oil release from porous media (remaining oil) involving processes such as

(i)                dissolution of inorganic carbonates by bacterial metabolites;

(ii)             Production of bacterial gases which decrease the viscosity of oil, thereby promoting its flow;

(iii)           production of surface-active substances or wetting agents by some bacteria; as well as

(iv)           the high affinity of bacteria for solids, later attached to crowd off the oil films

Table 1 Microbial products, their role in enhanced oil recovery, and some of the effects to solve production problemsa
Microbial product	Role in enhanced oil recovery	Some of the effects
aFormation damage; low oil relative permeability; trapped oil due to capillary forces; poor sweep efficiency channeling; unfavorable mobility ratio; low sweep efficiency; water or gas coning.
Gases (H2, N2, CH4, CO2)	•Reduce oil viscosity and improve flow characteristics• Displace immobile• Sweep oil in place	•Improved oil recovery by gases• Miscible CO2 flooding
Acids (low molecular weight acids, primarily low molecular weight fatty acids)	•Improve effective permeability by dissolving carbonate precipitates from pores throat. Significant improvement of permeability and porosity• CO2 produced from chemical reactions between acids and carbonate reduce oil viscosity and causes oil droplet to sweel	•Enhanced oil flooding
Solvents (alcohols and ketones that are typical cosurfactants)	•Dissolve in oil reduce viscosity• Dissolve and remove heavy, long chain hydrocarbons from pore throat (increase effective permeability)• Involved in stabilizing and lowering interf. tension that promotes emulsification• Reduce interfacial tension	•Emulsification promotion for increased miscibility
Biosurfactants	•Reduce interfacial tension between oil and rock/water surface which causes emulsification; improving pore scale displacement• Alter wettability	•Microbial surfactant• Flooding
Biopolymers	•Improve the viscosity of water in waterflooding and direct reservoir fluids to previously unswept areas of the reservoir• Improve the sweep efficiency of waterflood by plugging high permeability zones or water-invaded zones• Control of water mobility	•Microbial permeability modification (selective plugging)
Biomass (microbial cells)	•Physically displace oil by growing between oil and rock/water surface• Reversing wettability by microbial growth• Can plug high permeability zones• Selective partial degradation of whole crude oil• Act as selective and nonselective plugging agents in wetting, alteration of oil viscosity, oil power point, desulfuration	•Same biopolymers

Table 2 Key mechanisms for enhanced oil recovery in MEOR

Pure or mixed cultures of Bacillus, Clostridium, Pseudomonas, gram Molasses 2-4%• Molasses and ammonium nitrate addition• Free corn syrup + mineral salts• Maltodextrine and organic phosphate esters (OPE)• Salt solution• Sucrose 10% + Peptone 1% + NaCl 0.5-30%• Brine supplemented with nitrogen and phosphorous sources and nitrate• Biodegradable paraffinic fractions + mineral salts• Naturally contain inorganic and organic materials + N, P sources

negative rods• Mixed cultures of hydrocarbon degrading bacteria• Mixed cultures of marine source bacteria• Spore suspension of Clostridium• Indigenous stratal microflora• Slime Pure or mixed cultures of Bacillus, Clostridium, Pseudomonas, gram-negative rods• Mixed cultures of hydrocarbon degrading bacteria• Mixed cultures of marine source bacteria• Spore suspension of Clostridium• Indigenous stratal microflora• Slime-forming bacteria• Ultra microbacteria