Aerobic Microbial Enhanced Oil Recovery for Offshore Use

8/12/2019 Aerobic Microbial Enhanced Oil Recovery for Offshore Use

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SPEIDOEocietyof US. DepartmentPetroleum Engineers of Energy

SPEIDOE 24204Aerobic Microbial Enhanced Oil Recovery for Offshore UseEgil Sunde,* Statoil AIS, and Janiche Be eder, R.K. Nilsen, and Terje Torsvik, U. of BergenSPE Member

Copyright 1992, Society of Petroleum Engineers Inc.This paper was prepared for presentation at the SPE IDO E Eighth Symposium on Enhanced Oil R ecovery held in Tulsa, Oklahoma, April 22-24, 1992.This paper was selected for presentation by an SP E Program Com mittee following review of information contained in an abstract subm itted by the au thor s). Contents of th e pap er,as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author s). The material, as presented, does not necessarily reflectany position of the Society of Petroleum Engineers, its officers, or mem bers. Papers presented at SP E meetings are subject to pub licat~oneview by Editorial Committees of the Societyof Petroleum Engineers. Permission to copy is restricted o an a bstract of not more than 300words. Illustrations may not be copied. Th e abstract should contain conspicuous acknowledgme ntof where and by whom the paper is presented. Write Librarian Manager, SPE, P.O. Box 833836, Richardson, TX 75083383 6, Telex, 730989 SPEDAL.

ABSTRACTAerobic microbial enhanced oil recovery (MEOR), basedon the ability of oil degrading bacteria to reduce theinterfacial tension between oil and water, is reviewed.This process implies pumping water containing oxygenand mineral nutrients into the oil reservoir to stimulategrowth of aerobic oil degrading bacteria.Based on core flood experiments, the amount of bac-terial biomass responsible for dislodging the oil iscalculated.The results show that the process is limited by theamount of oxygen available for bacterial oil degradingand that on a weight/weight basis the bacterial biomasswas more efllcient than synthetic surfactants in dis-lodging the oil.Calculations show that it is feasible, on most offshoreplatforms, to instal equipment to handle the process.Further, calculations have been performed on theeconomics of the process, and the results indicate a costof 0.84 o 4.6 US per incremental mS oil produced.

INTRODUCTIONThe use of microorganisms to enh nce oil recovery(MEON has for many years been considered as a poss-ibility. Successful field trials have, in the later years,been reported both from the US Australia and EasternEurope (ref. 1 .The method used has been to inject.sugar solution (app. 5%)with nutrients and adaptedanaerobic bacteria into the formation.References and illustrations at end of paper

However, this is not a viable method for the largeoffshore fields, due to the huge amount of sugar needed.Typical 3000metric tomes of sugar per day must beused. in order to treat all injectors on a North Seaplatform.Using residual oil as the carbon source and injectingoxygen and nutrients togetherwith aerobic oil degradingbacteria can, on the other hand, be a technical andeconomical viable MEOR process offshore. Successfulfield-trials with thismethod have been performed in theUSSR (ref. 2, 3 .The theory for aerobic MEOR is that bacteria need tolower the interfacial tension between oil and water inorder to grow on oil. With low interfacial tension the oilwill be dislodged from the rock and transportedwith thewater. The oil industry has used this bacterial processto clean oil spill from beaches and to emulsilj oil slicksinto the water column.When oil degrading bacteria, oxygen and nutrients areintroduced into reservoir rock, a biofilm w llbe built oncontact with oil. Oil will then be dislodged by bacterialaction and transported towards the producer. When thecarbon source is depleted as oil is removed from theinjection well area, the active b i o h will move furtherinto the reservoir and reestablish in areas with sufficientoxygen and carbon supply. With s d c i e n t oxygensupply this process w ll continue throughout the reser-voir until all the oil has been removed.There are however limitations to this process. Theamount of oxygen traneported to the site of the residualoil is one, the generation of H,S (reservoir sourind fromsulphate in the seawater and weight of equipment andlogistic problems might be others.


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2 AEROBIC MICROBIAL ENHANCED OIL RECOVERY FOR OFFSHORE USE SPE 242Based on laboratory experiments and model calculations, this paper presents possibilities and limits-tions of the application of aerobic MEOR in offshoreAelds..

LABORATORY EXPERIMENTSMethodsA mixed bacterial culture was prepared from oil/watersamples collected at an oil refinery. The bacteria weregrown aerobically at 45OC on mineral medium, Table 1with North Sea Model Oil as carbon source. The mediumwas made up in disttlled water to a total volume of 1liter. The pH was 8.0. For bacterial enrichment the 0.1g/l North Sea Model Oil was added as a carbon source.For anaerobic flooding the mineral medium was reducedby flushing with nitrogen gas and addition of 10 mg/lsodium dithionite. For aerobic flooding the mediumwasflushed with airCore floods were performed as shown in figure 1.Themain components were a sandstone core, an injectionfluid reservoir and a hydraulic pump. The hydraulicpump was used to pump the mineral medium fkom theinjection fluid reservoir through the core. The core, aHopeman sandstone embedded in araldite, was placedin an incubator at 45OC. Properties are listed in Table 2.The evacuated core was flushed three times with nitro-gen gas and then saturated with the anaerobic mineralmedium. The mineral medium was then displaced withNorth Sea Model Oil. The oil was then produced from thecore by displacing with the anaerobic mineral medium,a t a flow rate of 0.1 mllmin. After one pore volume, 61ml oil was left in the core. Further flooding with anaero-bic mineral medium (four pore volumes) did not producemore oil.For the lVlEOR-expment 100 ml of mixed bacterialculture containing 6 x lo7bacteria per ml was injectedinto the core. The core was then flooded with 23 porevolumes of oxygenated mineral medium. The con-centration of oxygen at the core inlet was 1mg/l. Duringflooding, oxygen consumption, oil production andbacterial counts were monitored at the outlet of the core.ResultsBacteria were detected at the core outlet after 1 porevolume. The concentration was 1x 10 bacteria/ml, andremainedconstant throughout the experiment. Measure-ments showed tha t a l l the oxygen was consumed duringflooding, a n indication of bacterial activity within thecore.Oil production started after flooding with Cwo porevolumes of aerobic medium. For the next 21porevolum-es an average of 0.3 ml oil was produced per porevolume, giving a total of 6.2 mloil. Oxygen consumptionduring flooding was 2.5 mg. This means that 2.5 ml oilwas produced per mg oxygen consumed.

CALCULATIONSQuestions oRen raised in connection with MEOR processes are: - Is all the oil eaten by the bacteria?

- Will the bacteria plug the formation?How much food do the bacteria need?- Can oxygen be supplied to the bacteriaThe following items will therefore be highlighted:1 Oil consumption by the bacteria2 Biomass product3on3 Nutrient requirements4 OxygenavailabilityBasis for the calculations are:- 0 is the limitingfactor for bacterial growth- laboratory results hat indicated a producttan of 2.5

ml oil per mg oxygen are used.his is equivalent to 400 rams oxygen per inuemenM n3 of oil.

- bacterial growth equation:Calculations of bacterial oil consumtion are based onthe general composition of bacteria with respect tocarbon fCf,hydrogen HI,xygen (O), nitrogen ndphosphorous P), nd complete aerobic degradation ododecane to produce biomass, carbondioxide andwater.For bacterial biomass the followin@;molar relations areused:

C:H:O = 1:2:1 andC:N:P = 100:10:2combined with the assumption that during aerobigrowth 50 of the carbon is incorporated into bac-terial biomass and o s respired to CO,, theserelations give rise to the followinggrowthequation:50/6 [C,,H.J 104 0, 5 N P =(C,, H,, 0, N, P) 50 CO, 58 H,O (1where C,,H,,, dodecane, is used a s an example for oiand C,H,,0,N5P is the bacterial biomass.

1 OIL CONSUMPTIONThe absolute r n - a oil comumption s occuringwhen one oxygen atom oxidises one hydrocarbonmolecule to an alcohol and the degradation processproceeds anaerobically. In our calculation (400 g 02/m3oil) the oil consumption per m3 of incremental oil wouldbe app. 5 litre.

Another core flooding,with different bacterial inoculum,produced 1.4 ml oil per mg oxygen consumed.


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4 EROBIC MICROBI L ENH NCED OIL RECOVERY FOR OFFSHORE USE SPE 242

IMPLICATIONS OF CALCULATIONSGeneral theories for MEOR are that increased oilprod-uction is a result of one or more of the following actions:

Surfactant productionAcid productionGas productionFormation blockageAssuming predominately aerobic growt and based onour calculations compiled in Table 3 it is unlikely thatacid and gas production and formation blockage willcontribute significantly to aerobic MEORLeftwith surfactant action as the mainmechanism, it isinteresting to compare aerobic MEOR with surfactantflooding.Highly active surfactant have, in core flooding experiments, produced oil equivalent to over 100 liters oil perkg of surfactant.Our corefloods produced an equivalent of 1000 iters per

iters of biomass. This is an efficiency ive times higherthan synthetic surfactant.The reason for the higher efficiency could be that thebacteria have a highly efficient way of reducing inter-facial tension and/or that the bacterial growth occursonly on oil/water interfaces (no adsorption on rockmatrix).The loss of surfactant by adsorption and diffusion inconventional low tension floods is a serious restrictionto economic field processes. The implication that nosurfactant is lost to the reservoir minerals and rocksurfaces in the MEOR process, makes for a more econo-mic process throughout the reservoir. Variations in con-centration of effective surfactant are unlikely to occur,so one would expect consistency of process behaviourbetween the injection point and production point.

DESIGNAND MATERIAL REQUIREMENTSOffshore platforms have severe limitations on space andweight. There are also problems in transferring largeramounts of material under hostile weather conditions.Most platforms have also an oxygen removal system andmild steel in the downstream water injection system.It is therefore of importance, before carrying out exten-sive research on any EOR topic for offshore use, to assesthe designated platforms ability to cope with the extrademands imposed by the selected process.With seawater injection it is important to reduce thesulphate content to below 50 mg/l to prevent extensivereservoir souring. There are already operating (Braeplatform) and being built (Tiffany field) sulphate reduc-ing membrane systems offshore. These are installed toreduce sulphate scale problems.

The desired oxygen concentration can easily be met byinstalling a smallair compressor to increase the oxygecontent of the injection water.Injecting oxygen containing highly puriiled water, i.e. ncarbon source for bacterial growth, requires no deoxygenating system and normally used water treatinchemicals, as oxygen scavengers, biocides, scaleinhibitors ect.For aerobic MEOR the key points are then to upgradpiping and pumps etc. to withstand oxygen rich watersinstall equipment to remove sulphate and add ir tinjection water. Handling and storage of requirenutrients will also require some facilities.

Comparable steel quality to that used upstream of thdeaerator tower could also be used downstream to thwell head, and coated tubing could be used in the wellThese investments are not substantial and equipmenwith this material quality is already installed in somflelds with severe corrosion on standard mild steeequipment.Su bhate removalA sulphate removal membrane system is the only largpiece of equipment that needs to be installed on thplatform.

s mentioned above, such plants are already beinoperated offshore to reduce scale problems, Sulpharemoval is also under consideration on some fields teliminate reservoir souring.When using aerobic MEOR, the deoxygenation plant cabe removed, which facilitates the installation of a suphate removal system.Information collected from a manufacturer, indicatethat the capital investment for a 50.000 m3/day plant app. 25 million US and the overall running cost is app0.20 US per m3 water.When producing the incremental oil with a watercut 80%, the cost per m3 of oil is 0.8 US for the sulphatremoval.

ir injected downstream of the high pressure pumps caserve a s oxygen supply.With an concentration of 100 g/m3 in the injection watthe air demand per day would be:50000 m3 water 0.1 kg 0,/m3 water x 3.63 m3 &/kg0 18150 m3air


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In pressurising air u p to 300 bar, the energy require-ment is app. 0.167 kwh per standard cubic meter air.The size of the compressor needed on the platform willthen be:18150 m3 air /davx 0.167 kwh = 126 kW24 hours/day

Nutrient reauirements Der dav ~ e rlafformIn this example we are using a platform that injects 50000 m3 of seawater per day, producing the incrementaloil at 80 watercut.The oil/water ratio is then 1/4 which means that theoxygen content in the injection water must be: 400grams/m3 x 1/4 = 100 grams m3 of water. With theearlier established nutrient to oxygen ratio of 0.1, theuse per day per platform of nutrients is: 50000 m3 waterx 0.1 kg 02/m3water x 0.1 kg nutrient/kg 0 = 500 KG.CONCLUSIONSThe following conclusions can be drawn on the poss-ibilities an d limitations of aerobic MEOR:

The amount of oxygen delivered to the site of theresidual oil is the limiting factor for the process.More work is needed to determine non bacterialoxygen consumption in resenroirs.It should be possible, on most platforms, toinstall and operate the necessary equipment toru he process.Based on calculations from laboratory findingsand an oil production at 80 watercut (sum-marized in table I) , the cost per incremental m3of oil produced, is 0,84 US approximately.In most cases i t is practical and economical poss-ible to recover oil with this process, v n if thefield process is over 50 times less efficientlythanthe laboratory results indicates, Table 4.

ACKNOWLEDGEMENTThe authors wish to thank Statoil for the funding of thestudy and the permission to publish this paper.

REFERENCESRef 1: Ivanov M.V. and Belyaev S.S., 1990. Biotech-nology of enhancement of oil recovery based onthe geochemical activity of microorganisms (FieldExperiments). Microbial Enhancement of OilRecovery - Recent Advances. pp. 42 1-432.

Ref 2: Belyaev S.S., Ivanov M.V., Mat.A.A. BorisovAYu. Pilot Tests of Biotechnology Applied toEnhance Oil Recovery. Proceedings, Sixth Euro-pean Symposium on Improved Oil Recovery. Stav-anger, 21-23 May 1991.Ref 3: Ivanov M.V., Belyaev S.S., Borzenkov I A . Glu-mov I.F., Ibatullin RR The enhancement of oilrecovery by microbial processes. Field ex-

periments. Proceeding of the conference onMicrobiology in the Oil Industry and Lubrication,Sopron (Hungary). 10-12 September 1991. pp.130- 136.Ref 4: azar I., 1990. MEOR H e d Trials Carried OutOver The World During The Last35Years. Micro-bial Enhancement of Oil Recovery Recent Ad-vances. pp, 485-530.Ref 5: Zoss L.M., Suciu S N and Sibbitt W.L. TheSolubility of Oxygen in Water. Trans. ASME, 76.pp. 69-71. (1954).

T BLE

Content of mineral medium per liter of distilled water.

Vitamin solution 0.5mI Trace element solution I 0.1 m

T BLE 2Core data before s tart of MEOR

'l-I'Pe Hopeman sandstoneVolume 884 cm3Pore Volume 166 cm3Permeability 700 mDResidual oil 61 cm3Wettability Water wet


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SP 2420TABLETABLE

Calculated figures per incrementalcubic meter of oil produced at 80 water cut.Calculated figures per incremental cubic meter oproduced i the oxygen to oil produced ratio is 50higher than indicated fiom the laboratory results.

Amount I Cost I l Amount I CostI oil consumption I 0.5 iter I - I

Biomass production 1.9 -

Compressed ir 1.45m3 0.02USNutrient requirementI S u l ~ ha t eemoval I - I 0.80US I

0.04kg

1 m3 incremental oil produced per 400 gram oxygeninjected.

0.02 US

Sum

Biomass production 95 iter

0.84 US

Oil produced at93% watercut and0 oncentratiinjected water is 1.000gram

Nutrient requirementCompressed irSulphate removalSum

fOilReservoir

2 g72.5m3

Pump

1.00 US1.00 US2.60 US4.60US

Injection core IFluidReservoir Incubator Sampleollector

Fig 1 SCHEMATIC DRAWING OF THE FLOW RIG.

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Aerobic Microbial Enhanced Oil Recovery for Offshore Use