Use of Starved Bacteria To Increase Oil Recovery - ACS Symposium

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Use

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Starved Bacteria To Increase Oil Recovery

Hilary M . Lappin-Scott, Francene Cusack, F. Alex MacLeod, and J. William Costerton Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada

Limitations i n present oil recovery methods leave the majority of oil as unobtainable i n the reservoir. Therefore, any technique that increases or enhances the recovery rate of this resource would have great p o t e n t i a l for field applications. Our interest l i e s i n utilizing microorganisms to a s s i s t i n enhanced recovery by v i r t u e of their growth properties. We report on our recent laboratory data i n model rock s t r a t a . Our laboratory data demonstrate a new method of blocking the high permeability formations using starved forms of bacteria. It also has applications to control o i l w e l l coning. Estimates suggest that a maximum range of between 8-30% of the t o t a l oil is presently recovered from petroleum reservoirs leaving vast quantities underground as the focus for developing new techniques to increase recovery rates. One recovery method now i n use i s the waterflooding of d i f f e r i n g permeability rock strata (Fig. 1 ) . As the waterflood commences the high and low permeability zones are oil saturated (Fig. 1A). The waterflood follows the routes of least resistance, that i s the high permeability channels, and acts as an energy force to push out any oil along i t s path. However, once the oil has been displaced from these zones the water continues to follow the same course leaving the lower permeability zones unswept and therefore full of oil (Fig. IB). The process of blocking off the higher permeability strata and d i v e r t i n g the waterflood to other unswept zones i s c a l l e d selective plugging. In order to be e f f e c t i v e , the plug must penetrate throughout the high permeability zone or the water w i l l return p r e f e r e n t i a l l y from the lower back to the higher permeability s t r a t a . If a shallow plug i s established (Fig. IC) the waterflood i s i n i t i a l l y blocked from the higher permeability strata and pushes out some o i l . However, beyond the plug the waterflood returns to the high permeability zone leaving much o i l i n the low permeability s t r a t a . With a deeper plug i n the high permeability strata the waterflooding i s forced to stay i n the lower permeability zone and push the o i l out (Fig. ID) u n t i l most of the o i l i s drained (Fig. IE). 0097-6156/89/0396-0651$06.00/0 o 1989 American Chemical Society Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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water in

Injection well

water & oil out

Production well

Figure 1. Schematic diagram of the e f f e c t s of shallow and deep plugs on enhanced o i l recovery.

Borchardt and Yen; Oil-Field Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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Several agents are currently used for plugging high perme a b i l i t y strata. These include small fibers that are carried i n the waterflood and deposited i n the high permeability zgnes and chemical reactions forming insoluble precipitations . Some of the current methods available, for example polymers or foams, are subject to deterioration and are costly. This gives them limited application as they are not able to penetrate deep into the s t r a t a . In some reservoirs another problem develops that reduces o i l recovery, c a l l e d coning. This occurs most commonly when water l i e s below heavy o i l i n the reservoir. During primary recovery instead of the o i l being pumped out, water, being of lower v i s c o s i t y , i s p r e f e r e n t i a l l y pulled to the surface. Continued pumping only succeeds in g u l l i n g up more water, thus reducing or halting further o i l recovery ^ ^ Crawford ' reported that bacteria could be used as selective plugging agents and have the a b i l i t y to penetrate the high perme a b i l i t y areas. Another advantage i s that bacteria can grow i n the rock and^produce plugging both by their growth and^têir growth products . Research at the University of Oklahoma ' demonstrated that when bacteria were injected into two sandstone cores of d i f f e r ing permeabilities the bacteria p r e f e r e n t i a l l y grew and plugged up the higher permeability core f i r s t . However, when f u l l - s i z e d bacteria, 2.0 um or more i n length, are injected into s o l i d matrices the bacteria c o l l e c t at the i n l e t i n a sticky ma^s^gontaining micro b i a l growth and growth products, called biofilms ' and the plug i s referred to as a skjnplug. Reducing the concentration of bacteria to approximately 10 /ml reduced the opportunity for skinplug formation and this could be further reduced by using dormant, smaller forms of bacteria. The smaller size of dormant bacteria, that i s spores or starved bacteria, together with their absence of sticky growth products may allow them to travel further into rock strata. Microorganisms have been reported to decrease substantially i n size as a response to low nutrient conditions . Then, after a period of starvation when the organisms exist i n a dormant state, they commence growth again and return to f u l l size when given nutrients . Our work at the University of Calgary attempted to harness these changes i n c e l l size during starvation-resuscitation as a method for enhanced o i l recovery. We considered that the smaller c e l l size may enable them to penetrate deeper into rock s t r a t a than f u l l - s i z e d bacteria. By i n j e c t i n g organisms i n a starved state into rock then giving them growth nutrients would allow them to grow and plug the rock. Further waterflooding would bypass these plugged regions and sweep the areas containing o i l . Starved bacteria may also be used to control coning. They may be injected at the oilrwater interface then resuscitated with nutrients. B a c t e r i a l growth w i l l forma a deep pancake of sticky slime to physically separate the water from the o i l and prevent any more water being sucked to the surface. K l e b s i e l l a pneumoniae was isolated as a representative microorganism from produced water . The bacterium was starvedîn phosphate buffer s a l t s solutions at concentrations of either 10 /ml or 10 /ml. During starvation periods of up to 24 days the b a c t e r i a l c e l l s changed i n size and shape from rod-shaped, up to 2.2 um long,



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producing sticky slimes of polysaccharide-containing biofilms to spherical or small rods 0.5 um by 0.25 um with l i t t l e or no ^ o f i l m (Fig. 2). Such microorganisms are termed ultramicrobacteria (UMB). We investigated the a b i l i t y of the UMB to grow and resuscitate using d i f f e r e n t nutrients. One contained a r i c h mixture of growth substances, c a l l e d Brain Heart Infusion or BHI. The BHI was added at half of the manufacturers recommended concentration as this was s u f f i c i e n t to support rapid growth. Another nutrient contained only one carbon source, c a l l e d sodium c i t r a t e medium or SCM. The SCM was added at concentrations of 7.36 g/1. BHI was a fast acting nutrient and supported rapid resuscitation i n 4 hours, SCM wa^ a slow acting nutrient and supported resuscitation i n 8 hours After establishing that microorganisms from o i l w e l l s could decrease i n size and form UMB then return to f u l l size when given nutrients i n laboratory growth cultures, we investigated whether the UMB were able to penetrate deeper when injected into porous matrices than t h e i r f u l l sized counterparts. The experimental core flood apparatus consisted of a constant pressure, variable flow rate i n j e c t i o n system . The pressure was maintained at 3.5 p s i . In a comparative study using sintered glass bead cores with permeabilities og between 6 and 7 Darcys, one set of cores were injected with 10 /ml K. pneumoniae starved for 4 weeks, the other with 10 /ml of the f u l l sized bacteria grown on SCM . The f u l l sized cultures blocked the cores quickly and reduced the permeability to less than 1% of the o r i g i n a l value with the addition of 500 pore volumes. The starved bacteria only reduced the permeability to 82% despite the addition of i n excess of 800 pore volumes . After the injections were completed the glass bead cores were cut up into equal size sections and examined by electron microscopy to establish the position of the bacteria within the cores. The electron microscopy of d i f f e r e n t sections of cores treated with f u l l sized c e l l s showed that a mass of large rod-shaped bacteria was located at the core i n l e t . The bacteria had produced polysaccharides and the b i o f i l m which plugged the core i n l e t . With the starved cultures the UMB were evenly distributed throughout each of the core sections with l i t t l e or no b i o f i l m apparent. From t h i s work, we were able to conclude that starved K. pneumoniae was able to penetrate deeper into s o l i d matrices than f u l l sized c e l l s as a result of t h e i r smaller s i z e , less sticky glycocalyx and reduced b i o f i l m production. Another series of experiments used sandstone cores previously injected with starved bacteria to investigate the a b i l i t y of the ^ bacteria to grow within rock cores when given a suitable nutrient Berea sandstone cores of 200 and 400 m i l l i d a r c y (md) permeabilities were used as they were considered to be more representative of reservoir conditions than the glass bead cores. ^The sandstone cores were injected with 300 to 450 pore volumes of 10 /ml starved bacteria u n t i l the cores contained an even d i s t r i b u t i o n of bacteria (Fig. 3A & B) and the core permeabilities were between 13% and 18%. SCM nutrient was injected through the cores (Fig. 3C) u n t i l the core permeability f e l l to 0.1%, t h i s required 360 pore volumes of SCM. The starved bacteria resuscitated by u t i l i z i n g the SCM and grew within the sandstone forming a deep b a c t e r i a l plug composed of c e l l s



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Figure 2. Starved (A) and f u l l - s i z e d (B) K l e b s i e l l a pneumoniae in laboratory cultures viewed through an electron microscope. The sizes and shapes of the c e l l s d i f f e r markedly. The bar represents 1 um.

Bacteria

3 CM nutrient

BHI _ nutrient

iliiiiiiii;

IB i

Figure 3. Diagrammatic representation of the plugging of rock cores with resuscitated starved bacteria. See text f o r d e t a i l s .



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Figure 4. Scanning electron microscopy of starved (A) and nutrient stimulated (B) K l e b s i e l l a pneumoniae i n sandstone rock cores. The bar represents 5 um.



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and glycocalyx (Fig. 3D). The r e s u s c i t a t i o n followed a simjâr pattern to that reported i n laboratory batch growth systems , that i s , a difference i n r e s u s c i t a t i o n rates was observed with SCM and BHI. With SCM the slower resuscitation permitted a nutrient flow to a l l of the starved bacteria i n the sandstone and the subsequent growth produced a deep plug throughout the entire core (Fig. 3C & 3D). With BHI, a 95 pore volume i n j e c t i o n resulted i n a drop i n permeability to 0.5%. Resuscitation was so rapid that the growth of bacteria by the core i n l e t blocked o f f the supply of nutrients to lower down the core r e s u l t i n g i n a shallow b a c t e r i a l plug only at the top of the core (Fig. 3E & 3F). Sectioning and examination of the sandstone cores using scanning electron microscopy showed large differences i n the bacteria before and a f t e r nutrient additions (Fig. 4A & B). The nutrient fed bacteria were observed to have increased noticeably i n size and a mass of b i o f i l m was produced. The starved bacteria were s t i l l tiny and singular with l i t t l e or no biofilm. We also investigated several cost reduction exercies, such as, a) giving the starved bacteria short bursts of nutrient (less than 50 pore volumes) instead of a continuous flow and b) i n j e c t i n g fewer starved bacteria into the core (150 pore volumes) before nutrient i n j e c t i o n . Both s t i l l resulted i n deep b a c t e r i a l plugs when SCM was used as a nutrient. Other experiments are planned to study the location, d i s t r i b u tion and resuscitation of ultramicrobacteria i n large threedimensional sandpacks. Such studies w i l l allow a more r e a l i s t i c approximation of reservoir conditions than the u n i d i r e c t i o n a l core studies. We do not consider that the ultramicrobacteria w i l l reach or grow i n areas where residual o i l i s located. Selective plugging involves blocking the high permeability zones already drained of oil. We consider that the i n j e c t i o n of ultramicrobacteria w i l l be carried, l i k e waterflood operations, to the areas of the strata already drained of o i l and permit them to disperse through pore spaces and resuscitate i n these areas. Conditions d i f f e r i n each reservoir with respect to temperature, pressure and s a l i n i t y . No one microorganism w i l l be expected to survive, grow and plug a l l these d i f f e r e n t reservoirs. We suggest that a bacterium i s chosen from laboratory c o l l e c t i o n s that cover a range of environmental conditions best suited to the p a r t i c u l a r well. In summary, care must be taken to i n j e c t nutrients that do not encourage rapid growth as undesirable shallow b a c t e r i a l plugs form (Fig. 3F). With the correct nutrient package, such as SCM i n this instance, a deep plug w i l l form throughout the s t r a t a (Fig. 3D). In conclusion, our laboratory based studies demonstrate that starved bacteria may be used to physically block rock s t r a t a already drained of o i l . Further recovery operations can then deal with strata s t i l l containing o i l and thus enhance recovery rates. Literature Cited 1. 2.

Moses, V. Microbiol. S c i . 1987, 4, 306-309. Breston, J . N. J . P e t r o l . Technol. March 1957,

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Hower, W. F.; Ramos, J. J . P e t r o l . Technol. January 1957, 137-140. Crawford, P. B. Producers Monthly 1961, 25, 10-11. Crawford, P. B. Producers Monthly 1962, 26, 12. Jenneman, G. E.; Knapp, R. M . ; McInerney, M. J.; Menzie, D. E.; Revus, D. E . Soc. P e t r o l . Eng. J. Feb. 1984, 33-37. Raiders, R. A.; Freeman, D. C.; Jenneman, G. E.; Knapp, R. M . ; McInerney, M. J.; Menzie, D. E . Paper SPE 14336 presented at 60th Annual Technical Conf. & Exhibition of Soc. P e t r o l . E n g . , Las Vegas, NV, 1985. Raiders, R. A.; McInerney, M. J.; Revus, D. E.; T o r b a t i , H. M . ; Knapp, R. M . ; Jenneman, G . E . J . Industr. Microb., 1986, 1, 195-203. Shaw, J. C.; Bramhill, B . ; Wardlaw, N. C.; Costerton, J . W. Appl. & Envir. M i c r o b i o l . , 1985, 50, 693-701. MacLeod, F . A.; Lappin-Scott, H. M . ; Costerton, J. W. Appl. & Envir. M i c r o b i o l . , 1988, 54, 1365-1372. Jang, L.-K.; Chang, P. W.; Findley, J. E.; Yen, T. F . Appl. & Envir. M i c r o b i o l . , 1983, 46, 1066-1072. Novitsky, J. A.; Morita, R. Y. Appl. & Envir. M i c r o b i o l . , 1976, 33, 635-641. T o r e l l a , F.; Morita, R. Y. Appl. & Envir. M i c r o b i o l . , 1981, 41, 518-527. Lappin-Scott, H. M . ; Cusack, F.; MacLeod, F. A.; Costerton, J. W. J . Appl. Bacteriol., 1988, 64, 541-549. Lappin-Scott, H. M . ; Cusack, F.; Costerton, J . W. Appl. & Envir. M i c r o b i o l . , 1988, 54, 1373-1382.

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R E C E I V E D January 13, 1989


Use of Starved Bacteria To Increase Oil Recovery - ACS Symposium

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