CA2689191C

CA2689191C - Method of oil treatment

Info

Publication number: CA2689191C
Application number: CA2689191A
Authority: CA
Inventors: Hans Kristian Kotlar
Original assignee: Statoil ASA
Current assignee: Equinor ASA
Priority date: 2009-12-23
Filing date: 2009-12-23
Publication date: 2017-07-11
Anticipated expiration: 2029-12-23
Also published as: CA2689191A1

Abstract

The invention provides a method of oil treatment, e.g. following extraction of oil from a subterranean hydrocarbon reservoir, said method comprising incubating oil in an incubation vessel with a microorganism capable of digesting said oil, and recovering the digested oil.

Description

METHOD OF OIL TREATMENT
FIELD OF THE INVENTION
This invention relates to a method of oil treatment, e.g. immediately following extraction of oil from a subterranean hydrocarbon reservoir, and to compositions for use in such methods.
BACKGROUND
Hydrocarbons, i.e. gas and oils, are a limited resource and thus it is important to maximize the amount of oil that is recovered from underground reservoirs.
For certain reservoirs, particularly heavy oil reservoirs in which the oil contains large quantities of long chain hydrocarbons, paraffins, waxes, aromatics (including polyaromatic hydrocarbons - PAH), terpenoids, asphaltenes, etc., oil sand or shale reservoirs, and bitumen reservoirs the techniques currently used result in the recovery of less than 10% wt. of the oil in the reservoir. To a large extent this is because the oil is of such a high viscosity, or otherwise flows so poorly, that only limited quantities will reach the production wells.
One approach that has been adopted to this problem is to inject superheated steam down injection wells above the production wells, e.g. in substantially horizontal sections of the bore holes where the injection bore hole is above the production bore hole. The temperature increase resulting from superheated steam injection serves to reduce the viscosity of the heavy oil which then, under the influence of gravity, flows more readily into the production bore hole. This procedure has been referred to as steam-assisted gravity drainage (SAG-D) or VAPEX.
A further approach to increasing hydrocarbon recovery is hot solvent extraction in which a heated organic solvent is injected into the matrix to reduce the viscosity of the hydrocarbon and improve its flow characteristics in the matrix. In this technique, injection may be into an injection bore hole (i.e. as with steam injection)

- 2 -or it may be into the production bore hole. Typically the hot solvent used is selected from naphtha, diesel, toluene, and other hydrocarbon fractions. The injection temperature will typically be in the range 20 to 400 C, especially 80 to 100 C.
Yet another extraction enhancement procedure is cold heavy oil production with sand (CHOPS) which involves sand influx into the production well. Another procedure is hydraulic fragmentation (fracking) of the matrix at the production well.
Further examples of enhanced oil recovery techniques for heavy oil, oil sand or bitumen reservoirs include cyclic steam stimulation (CSS), and pulsed pressure flow enhancement. Down-hole generation of gases to increase down-hole pressure and hence oil flow into the production well may also involve direct contact steam generation and thermal oxidation processes (to generate CO2 from combustion of hydrocarbons down-hole).
After oil extraction, processing steps are often required to yield an oil with suitable properties for transport and refining. Such extra processing steps are especially important for hyrocarbons extracted from heavy hydrocarbon reservoirs. Post-extraction processing steps which are conventionally used include heating, partial refining (e.g. cracking) and dilution with light crudes or synthetic oils.
However, these techniques are cumbersome, environmentally unfriendly and improvements and alternatives are desirable.
SUMMARY OF EMBODIMENTS OF THE INVENTION
We have now realized that oil recovery may be enhanced and post-extraction processing simplified if the extracted hydrocarbon is incubated with heavy oil-degrading microorganisms, especially under conditions which replicate those of a hydrocarbon reservoir, e.g. at high temperature and pressure.
Thus viewed from one aspect the invention provides a method of oil treatment, especially where said oil is obtained directly from a subterranean hydrocarbon

- 3 -reservoir, and particularly where said oil is a heavy oil, said method comprising incubating said oil in an incubation vessel with a microorganism capable of digesting said oil, and recovering the digested oil. The method of the invention is thus preferably effected topside at or near the well head and/or at the refinery site.
Microorganism incubation is effected in one or more suitable vessels and incubation may be initiated by injection of the microorganism through a plurality of injection points in the (or each) vessel, e.g. 5 to 20 such injection points in each vessel.
Incubation may also be initiated by injection of the microorganism into the oil, e.g.
at elevated temperature and/or pressure, after recovery of the oil from a subterranean hydrocarbon reservoir but before, or during, injection of said oil into the incubation vessel. In the event that the incubation is carried out at elevated temperature or pressure (e.g. at a temperature and/or pressure which mimics the downhole conditions of a subterranean hydrocarbon reservoir which is the source of the oil and/or the microorganism), the microorganism is preferably a thermophilic and/or piezophilic microorganism.
The incubation vessels will typically be traditional crude oil storage tanks (e.g. made of stainless steel) and will typically be provided with a stirrer system (e.g.
blades or rotors) and/or be provided with different inlet dyes. The incubation vessels are preferably cylindrical in shape and will typically have a capacity of between about 1000 M3 and about 100,000 m3, especially between about 1500 m3 and about 5000 m3, at a crude oil temperature of between 20 and 110 C. In embodiments of the invention where higher temperature and/or high pressure incubation is desired, the incubation vessels will be chosen accordingly, for example being made of suitable materials and having the appropriate dimensions to enable safe operations at these conditions, e.g. using vessels known in the art.
By oil degrading or oil digesting it is meant that the microorganism (or microorganism mixture) is capable of chemically modifying oil to reduce the viscosity or wax, asphaltene or aromatics content thereof whereby to cause it to flow more freely. Such modification will generally involve fragmentation of one or more

- 4 -components of the oil (e.g. fragmentation of alkanes into smaller alkanes), ring opening in aromatic compounds, or opening or cleavage of other large organic compounds, for example asphaltenes. Desirably, the microorganisms cleave or fragment the oil components so as to render the oil viscosity sufficiently low as to allow transportation by pipeline with little or no dilution or heating.
Thus it is preferred that the microorganism used not simply be one that generates a surfactant or a gas (e.g. methane), and particularly preferably a microorganism cocktail is used which causes ring opening, especially in combination with a microorganism that causes hydrocarbon chain shortening and particularly where said cocktail bioconverts the heavy components (e.g. the asphaltenes). Preferred microorganisms for use according to the invention therefore include alkane chain-shortening microorganisms, aromatic ring opening microorganisms and asphaltene degrading microorganisms.
Many microorganisms (generally eubacteria or archae) are known to digest oil and such microorganisms may be used in the method of the present invention if they are capable of surviving at the temperatures and pressures contemplated for the incubations of the invention. Typical examples of microorganisms for use according to the invention include Bacillus sp., Therms sp., Pseudomonas sp., Geobacillus sp., Arthrobacter sp., Sphingomonas sp., Mycobacterium sp., Burholderia sp., Acinebacter sp., Thermovirga sp., Archaeoglobus sp., The rmosipho sp., Symbiobacterium sp., Methanosaeta sp., Epsilonproteobacterium sp., Syntrophus sp., Nocardioides sp., Deferribacter sp., Chloraflexi sp., Pelobacter sp. and Desulfobul bus sp., etc.
Preferably however the inoculate, the microorganism composition used in accordance with the present invention, will contain at least 2 and preferably at least 3 different microorganism species, in particular at least one capable of chain-shortening alkanes and at least one capable of ring opening aromatics, especially preferably with at least one capable of asphaltene degradation.

- 5 -Examples of microorganisms capable of chain-shortening alkanes include Bacillus sp., Geobacillus sp., Acinebacter sp., Methanosaeta sp. and in particular Acinebacter venetianus, Bacillus thermoleovorans , Bacillus aeolis and Geobacillus thermodenitrificans while examples of microorganisms capable of degrading aromatics include Nocardioides sp., Geobacillus sp., and Syntrophus sp., eg Geobacillus subterraneous. Use of Thermus sp. will result in decrease of aromatics, resins and asphaltenes and reduced viscosity, eg Thermus strains SP3, C2 and (see Hao etal. J. Can. Petrol. Tecnol. 43:36-39 (2003), Can. J. Microbiol.
50:175-182(2004), and J. Petrol. Sci. Eng. 43:247-258(2004)). Use of Pseudonionas sp.
will result in n-alkane and PAH degradation and reduced viscosity, eg Pseudomonas aeruginosa. Moreover, Therms brockii is capable of degrading hexadecane and pyrenes (see Geitkenhaucr et al., Water Sci Technol 47: 123-130(2003)).
Rather than producing a microorganism inoculation composition by mixing individual microorganisms, it is possible and indeed preferable to use microorganism cocktails obtained from or developed from naturally occurring microorganism communities, e.g. microorganism communities from subterranean hydrocarbon reservoirs, from oil shales, bitumen sources, or, especially from mud volcanoes. Likewise appropriate microogranisms may of course be produced by mutagenesis or by genetic engineering.
It is especially preferred that the inoculate contain microorganisms selected from the species Bacillus thermoleovorans , Therm us brockii, Syntrophus aciditrophicus, Acinebacter venetianus, Deferribacter desulfuricans, Thermosipho geolei, Thermosipho africanus, Symbiobacterium the rniophilium, Thermovirga lienii, Sphingomonas stygia, Sphingomonas aromaticivorans, Sphingomonas subterranean, Sphingomonas yanoikuyae, Pseudomonas putida, Burholderia sp., Archaeoglobus fulgidus, Pelobacter sp. and Desulfobulbus sp.. Particular deposited strains that can be used include Bacillus therrnoleovorans AB034902 (Genbank), Bacillus aeolis AY603079 (Genbank), Pseudomonas aeruginosa AM087130(Genbank), Geobacillus thermodenitrificans DQ243788(Genbank), Geobacillus subterraneous DQ355385(Genbank), Sphingomonas stygia DSMZ12445, Sphingoinonas sp DSMZ

-

-6-7526, Sphingomonas sp DSMZ 11094, Sphingomonas aromaticivorans DSMZ
12444, Sphingomonas subterranean DSMZ 12447, Sphingomonas yanoikuyae DSMZ 6900, Pseudomonas putida NCIMB 9815, Pseudomonas putida NCIMB
9816, Pseudomonas putida NCIMB 10015, Methanosaeta sp. AJ 133791, Epsilonproteobacteria AY 570641, Syntrophus aciditrophicus CP 000252, Nocardioides sp. D 87974, Deferribacter desulfuricans AB 086060, Chlorflexi sp. AB 074961, Thermovirga lieniiDQ 071273, Archaeoglobus fulgidus DQ 131905, Thermosipho geolei AJ 272022, Acinebacter venetianus ATCC 31012 and Symbiobacterium sp. AB 052392. It is particularly preferred that it contain microorganisms of at least the species Sphingomonas sp., Pseudornonas sp., Burholderia sp., Therniovirga lienii, Archaeoglobus fulgidus, Acinebacter venetianus, ThermostPho geolii and Symbiobacterium sp., especially in combination with Pelobacter sp. and Desulfobulbu.v sp. Such mixtures are new and form a further aspect of the invention.
Viewed from this aspect, the invention provides a microorganism mixture for oil treatment, said mixture comprising microorganisms of at least two, preferably at least three, of the following species: Sphingonionas sp., Pseudomonas sp., Burholderia sp., Thermovirga lienii, Archaeoglobus fulgidus, Acinebacter venetianus, Thermosipho geolii, Symbiobacterium sp, Geobacillus sp., Pelobacter sp. and Desulfobulbus sp., in particular said mixture further comprising vitamins and =
minerals and preferably a mixture in liquid or dry powder form, and preferably alkane-free, eg isolated from any matrix or hydrocarbon in which it may occur naturally.
In particular, a combination of Sphingonzonas sp., Pseudomonas sp., and Burholderia sp. may be used, eg Sphingornonas stygia, Sphingomonas aromaticivorans, Sphingomonas subterranean, Sphingomonas yanoikuyae, Pseudomonas putida, and Burholderia sp., especially Sphingomonas stygia DSMZ12445, Sphingomonas sp DSMZ 7526, Sphingomonas sp DSMZ 11094, Sphingomonas aromaticivorans DSMZ 12444, Sphingomonas subterranean DSMZ
12447, Sphingomonas yanoikuyae DSMZ 6900, Pseudomonas putida NCIMB 9815,

- 7 -Pseudomonas putida NCIMB 9816, Pseudomonas putida NCIMB 10015, and Burholderia sp. In a related aspect, a combination of Sphingomonas sp., Pseudomonas sp., Burholderia sp., Geobacillus sp., Pelobacter sp. and Desulfobulbus sp. may be used.
In one embodiment, the inoculate comprises microorganisms that grow at atmospheric pressure, in a further embodiment the inoculate comprises microorganisms which are thennophiles and/or piezophiles.
Selecting appropriate combinations of microorganisms for use at ambient or near ambient conditions is thus relatively simple. A candidate microorganism or microorganism cocktail may be incubated with a sample of heavy oil, preferably from the site to be treated, and if a reduction in viscosity is achieved the candidate may proceed. For oil obtained from deeper fields the incubation is preferably effected at the down hole temperatures and/or pressures of the site from which the oil is to be treated. In both cases, the ability to withstand temperatures of 60 to 120 C, especially 70 to 100 C is preferred as such microorganisms may readily be injected into oil obtained directly from sites where steam or hot solvent injection has been used to obtain the oil to be treated (e.g. topside at or near the well head and/or at the refinery site). In this manner, any delay between steam or hot solvent injection and microorganism incubation is minimised and energy is saved.
The duration of incubation of the method according to the invention will typically be from 2 days to several months (e.g. 3 months), preferably from 3 to 7 days.
Preferred temperatures for incubation are between 0 and 120 C, particularly between 50 and 80 C and preferred pressures are between about 0.1 and 100 MPa, especially between about 0.5 and 10 MPa. Incubation vessels may be activated and inoculated with or without 02 present, this may depend on the nature of the microorganism cocktail used. Preferably, the method will be anaerobic (i.e. in the substantial absence of 02 to enable growth of anaerobic organisms) and with or without a nutrient supply (i.e. a supplementary nutrient source besides the oil for degradation) or electron acceptors. In one embodiment, hot organic solvent (e.g. at

- 8 -a temperature of between 50 and 80 C) is added to the incubation mixture at a level of between 0 to 50% by weight, preferably between 7 and 20% by weight. Other beneficial additives (e.g. surfactants) may be included in the incubation mixture.
Where steam or hot solvent injection has been used to obtain the oil for treatment according to the method of the invention, the timing of the microorganism injection into said oil should be such that the microorganisms are not injected into an environment in which the temperature is lethal. The delay time for microorganism injection may readily be calculated from the heat dissipation characteristic of the oil and from the oil temperature.
Screening of a microorganism cocktail is preferably done repeatedly, with an aliquot of the culture at the end of one incubation/digestion period then being presented with a fresh heavy oil sample to digest. This is important as degradation may require the contribution of one microorganism species after that of another and it may thus be necessary that all of the necessary species continue to grow.
Where, after several digestions, the microorganism population is stable, the candidate may be developed further.
Before injection into an incubation vessel, the microorganism inoculate may be mixed with oil to prime its enzyme systems.
Injection of the microorganism into an incubation vessel may if desired be preceded by, accompanied by or followed by injection of nutrients for microorganism growth, e.g. minerals and amino acids, or oil digesting enzymes. The injection of further carbon sources, eg ones such as acetate which are water-soluble, is particularly preferred.
Injection of the microorganism into an incubation vessel may if desired be preceded by mechanical disruption of the oil sample in the vessel around the injection site, e.g. to provide an initial reservoir for microorganism growth. Injection of the microorganism into an incubation vessel may also be effected in conjunction with

- 9 -steam or superheated water or organic solvent injection, e.g. at an injection temperature of 50-100 C, or of 100-400 C. This injection may precede microorganism injection (where the steam or solvent injection temperature is lethal to the microorganisms) or may occur simultaneously.
If desired, the microorganism inoculate may include microorganisms which generate gas and/or acid to assist in degradation of the oil sample.
The method of the invention can serve to reduce the usage or aggressiveness of the other hydrocarbon processing techniques, and so reduce their environmental impact.
The invention is especially applicable to heavy oils obtained from hydrocarbon reservoirs, e.g. to medium crude (31-22 API) to heavy crude (22-10 API) to extra heavy crude (<10 API) oils, and the microorganism incubation, particularly with thennophilic and/or piezophilic microorganisms, preferably follows treatment of the reservoir with at least one oil recovery technique selected from SAG-D, CHOPS, VAPEX, hot solvent extraction and hot water extraction.
Further, in accordance with an aspect of at least one embodiment there is provided a method of oil treatment comprising incubating oil in an incubation vessel with a mixture of microorganisms capable of digesting said oil, and recovering the digested oil, wherein said mixture of microorganisms comprises at least two of the following species: Sphingomonas sp., Pseudomonas sp., Burholderia Therinovigra lienii, Archaeoglobus fulgidus, Acinebacter venetianus, Thermosipho geolii, Symbiocacterium sp., Geobacillus sp., Pelobacter sp. and Desulforbulbus sp.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be illustrated by the following non-limiting Examples and the accompanying drawing, in which:
Figure 1 is a schematic of an incubation vessel for use according to the invention - 9a -which shows a vessel (1) comprising an oil inlet port (2), an oil recovery port (3) and a microorganism injection port (4).
DETAILED DESCRIPTION OF THE DRAWINGS
Example 1 Treatment of Zuata crude oil with microorganisms endo_genous to Argentine bitumen

- 10 ¨
Materials:
Bitumen (from Argentina) Treatment medium 1 (TMS1) content per litre: 5 g FeSO4=7H20, 0.29 g CuSO4=5H20, 0.44 g ZnSO4=7H20, 0.15 g MnSO4.1-120, 0.01 g Na2Moa42H20, 0.02 g CoC12=6H20, 50 ml cone HC1.
Treatment medium 3 (TMS3) content per litre: 2021.2 mg Na2SiO3.9H20, 445.5 mg NaF, 5651.7 mg K213407.4H20, 47.9 mg NaI03, 180.7 mg KA1(SO4)2=12H20, SnC12.2H20.
Treatment medium 4 (TMS4) content per litre: 346.8 mg NiC12=6H20, 101.4 mg Na2Se03.51-120, 18 mg V205, 14 mg K2Cr207,3.6 mg Na2W04.2.H20.
Vitamin stock solution (VSS) content per litre: 2.00 g biotin, 2.00 g folic acid, 10.00 g pyridoxine-HCI, 5.00 g thiamine-HC1.2H20, 5.00 g riboflavin, 5.00 g nicotinic acid, 5.00 g D-Ca-pantothenate, 0.10 g vitamin B12, 5.00 g p-aminobenzoic acid, 5.00 g lipoic acid.
Mineral medium (MM) content per litre: 0.9 g NH4NO3, 0.05 g CaC12=2H20, 0.2 g MgSO4=7H20, 3.06 g Na2HPO4-2H20, 1.52 g KH2PO4, 1 ml TMS1, 1 ml TMS3, 1 ml TMS4, 1 ml VSS. pH adjusted to pH 7Ø
Process medium 1 (PM1): Zuata crude oil (from Venezuela) 0.4 % (w/vol) in MM
Process medium 2 (PM2): Zuata crude oil 1.6% (w/vol) in Light Gas Oil (LGO), 1 % (vol/vol) in MM
Inoculation:
Bitumen samples (0.5 g) were inoculated into shakeflasks (Bellco, 250 ml) containing 50 ml PM1 or PM2.

- 11 -Cultivation:
The shake flasks were incubated at 50 C on a rotary shaker at 200 rpm and 90 %
humidity (Infors Multitron incubator) for 34 days.
Example 2 Treatment of Zuata heavy oil with microorganisms endogenous to a mud volcano Materials:
Mud from mud volcano Widdel Basal Salt Media B (WBSB) content per litre: 30.0 g NaCI, 0.15 g CaC12=2H20, 3.0 g MgC12=6H20, 0.9 g NRIN03, 0.5 g KCI, 0.18 g Na2SO4, 3.06 g Na2HPO4.2H20, 1.52 g KH2PO4, 1 ml TMS1, 1 ml TMS3, 1 ml TMS4, 1 ml VSS.
pH adjusted to 8.2.
Process medium 3 (PM3): Zuata crude oil dissolved 10% (w/vol) in heptamethyl nonane (RMN ¨ an inert solute) added 5% (vol/vol) to WBSB
Inoculation:
Mud samples (0.5 ml) were inoculated into shakeflasks (Bellco, 250 ml) containing 50 ml PM3.
Cultivation:
The shake flasks were incubated at 50 C on a rotary shaker at 200 rpm and 90 %
humidity (Infors Multitron incubator) for 28 days.
Example 3 Treatment of Linerle crude oil with microorganism cocktail Materials:
Microorganism cocktail (MC): A mixture of the following strains:
Pseudomonas putidaNC1MB 9815, NCLMB 9816 and NCIMB 10015 and

12 -Burkholderia sp isolates from bio-sludge from a refinery water treatment plant. The microorganisms were cultivated in inoculum medium (IM) for up to 24 hours and harvested by centrifugation (10 min, 5 000 x g). The cell-pellets were washed twice with MM medium (20 in!) and the pellet resuspended in MM medium (500 p.1).The microorganism cocktail (MC) was prepared by mixing the washed and resuspended microorganisms in equal concentrations.
Inoculum medium (IM) per litre: 20.0 g yeast extract, 1.0 g MgSO4=7H20, 5 g NaCl, pH adjusted to 7.5.
Process medium 4 (PM4): 5 % (vol/vol) heat-treated Linerle crude oil (from the Norwegian continental shelf, heated to 60 C for 2 hours) was added to MM.
Process medium 4 with yeast extract (PM4-YE): 5 % (vol/vol) heat-treated Linerle crude oil (from the Norwegian continental shelf, heated to 60 C for 2 hours) was added to MM containing 0.1 g yeast extract.
Inoculation:
The MC was inoculation into shakeflasks (Bellco, 250 ml) containing 50 PM4 or 50 ml PM4-YE to a final 0D660= 1Ø
Cultivation:
The shake flasks were incubated at 30 C on a rotary shaker at 200 rpm (Infors Multitron incubator) for 9 days.
Example 4 Treatment of Zuata heavy oil in sand with microorganisms from sediment Materials:
Microorganism inoculum (MI): A mixed inoculum of microorganisms isolated from sediment samples Sand column: Zuata crude oil mixed in a 9:36 weight ratio with barskarp sand,

- 13 -packed into glass columns (Omnifit).
Inoculation:
MI (5 ml, approx 10 9cells/m1) was added to the sand column after water flooding the column for 4 days.
Cultivation:
After inoculation, the sand columns were shut-in for 24 hours prior to circulation of MM was initiated. MM was circulated at a rate of 171 mUhour.
The results of this treatment of heavy oil in reservoir-like conditions is shown in Figure 2 of the attached drawings. Figure 2 shows the oil recovery from sand packs as a percentage of standard total original in place (STOOIP - right hand ordinate and plot) and the viscosity in mPa.s of the treated oil at a shear rate of 100 s-1 and 55 C
(left hand ordinate and bar chart). The left hand values are for Zuata heavy oil without treatment. The centre values are for Zuata heavy oil treated under the conditions specified in this Example. The right hand values are for Zuata heavy oil treated under the conditions specified in this Example, but with the addition of 5 g,/L acetate (eg sodium acetate) to the MM.
Example 5 Viscosity effect on crude oils The viscosity of treated and untreated heavy crude oil type I was determined at 30 C
at a shear of up to 1000 s-1. While untreated gave a viscosity value of 417 mPas, for the treated sample this was reduced to 130 rnPas. In a further test using Zuata crude oil, treated and untreated, in a radial reservoir model, at 60 C and a shear rate of up to 700 s-1, a significant reduction in viscosity was noted at all shear rates which became increasingly prominent at shear rates above 100 s-1.

Claims

CLAIMS:

1. A method of oil treatment comprising incubating oil in an incubation vessel with a mixture of microorganisms capable of digesting said oil, and recovering the digested oil, wherein said mixture of microorganisms comprises at least two of the following species: Sphingomonas sp., Pseudomonas sp., Burholderia sp., Thermovigra lienii, Archaeoglobus fulgidus, Acinebacter venetianus, Thermosipho geolii, Symbiocacterium sp., Geobacillus sp., Pelobacter sp. and Desulforbulbus sp.

2. The method of claim 1, where said oil is obtained directly from a subterranean hydrocarbon reservoir.

3. The method of claim 2, wherein said incubating is carried out a temperature or pressure, or temperature and pressure which mimics the downhole conditions of said subterranean hydrocarbon reservoir.

4. The method of claim 3, wherein the incubation temperature is between 0 and 120°C.

5. The method of claim 4, wherein the incubation temperature is between 50 and 80°C.

6. The method of any one of claims 3, 4 and 5, wherein the incubation pressure is between 0.1 and 100 MPa.

7. The method of claim 6, wherein the incubation pressure is between 0.5 and MPa.

8. The method of any one of claims 1 to 7, wherein said oil is a heavy oil.

9. The method of claim 8, wherein the heavy oil is less than 22 API.

10. The method of any one of claims 1 to 9, wherein incubation is initiated by injection of said mixture of microorganisms through a plurality of injection points in said incubation vessel.

11. The method of any one of claims 2 to 9, wherein incubation is initiated by injection of the mixture of microorganisms into the oil at elevated temperature or pressure, or elevated temperature and pressure, relative to ambient temperature and pressure, after recovery of said oil from the subterranean hydrocarbon reservoir but before, or during, injection of said oil into the incubation vessel.

12. The method of claim 11, wherein injection of the mixture of microorganisms is effected in conjunction with steam, superheated water or organic solvent injection.

13. The method of any one of claims 1 to 12, wherein said mixture of microorganisms comprises microorganisms of the species Sphingomonas sp., Pseudomonas sp., Burholderia sp., Geobacillus sp., Pelobacter sp. and Desulforbulbus sp.

14. The method of any one of claims 1 to 12, wherein said mixture of microorganisms comprises microorganisms of the species Sphingomonas sp., Pseudomonas sp., and Burholderia sp.

15. The method of any one of claims 1 to 12, wherein said mixture of microorganisms comprises microorganisms of the species Sphingomonas stygia, Sphingomonas aromaticivorans, Sphingomonas subterranean, Sphingomonas yanoikuyae, Pseudomonas putida, and Burholderia sp.