Appl Microbiol Biotechnol (1992) 36:833-835

Short contribution

Applied Microbiology

Biotechnology © Springer-Verlag 1992

Application of microbial enhanced oil recovery technique to a Turkish heavy oil

Kemal Behlulgil 1, Tanju Mehmetoglu 1, and Sedat Donmez 2

~ Petroleum Engineering Department, Middle East Technical University 06531, Ankara, Turkey z Agriculture Faculty, Ankara University, Ankara, Turkey

Received 6 September 1991/Accepted 31 October 1991

Summary. Microbial enhanced oil recovery utilizes mi- croorganisms and their metabolic products to improve the recovery of crude oil from reservoir rocks. In this study an anaerobic bacterium, Clostridium acetobutyli- cum was injected into a one-dimensional model reser- voir containing a Turkish heavy oil (Raman oil) at 38 ° C. This injection was followed by water flooding after a suitable shut-in period. Comparison of oil recov- ery results of pure water flooding runs with experi- ments in which bacterial concentration and shut-in pe- riods were varied indicated increases in oil recovery of about 12% of the original oil in place. This increase was attributed to changes in the viscosity and pH of the crude oil.

Introduction

Microbial enhanced oil recovery (MEOR), which is the newest technique in enhanced oil recovery, aims to im- prove oil recovery via in-situ biochemical processes. The application of the M E O R technique involves three main mechanisms by which the microorganisms sent into oil reservoirs can improve oil recovery (Knabe 1984). These can be classified as follows: 1. Splitting of heavy fractions in crude oil. 2. Generation of gases (CO2, N2, H2, CH4). 3. Production of chemicals (surfactants, solvents, acids, biopolymers).

When the types of microorganisms useful for differ- ent recovery mechanisms are investigated, it can be seen that Pseudomonas, Arthrobacter and some other aerobic bacteria are effective in consuming hydrocar- bons and Clostridium, Bacillus and Desulfovibrio species can produce gases and chemicals (Jack et al. 1985). The environmental factors that limit either the injectivity of cells, or their growth and metabolic products (Donald- son and Clark 1982) are temperature, permeability,

Offprint requests to: T. Mehmetoglu

acidity and salinity of the medium. As most reservoirs are essentially anaerobic, anaerobic bacteria are pre- ferred in field applications.

Research on MEOR shows that this technique can also be applied effectively to heavy oils (Jack and Thompson 1980). Based on these results, the applica- tion of M E O R to a Turkish heavy oil (Raman oil) was investigated in this study.

Materials and methods

In this work, MEOR application to Raman crude oil (densi- ty=0.9422 g/cm 3) was performed experimentally. These experi- ments consisted of one reference waterflood (RR-1) and six mi- crobial waterfloods (RM-I to VI).

Experimental equipment. The experimental set-up consisted of a fluid injection system, a one-dimensional model reservoir and a production section (Fig. 1). The fluid injection system consisted of brine, oil, microbial suspension and water injection sections. The one-dimensional reservoir model was essentially a stainless steel tube 100 cm in length and 6.2 cm in diameter. The packing mate- rial used was limestone grains between 14 and 35 mesh sizes (mean particle diameter=0.975 mm). The pore volume of the model was 1200 cm 3 when filled completely with 4680g dry crushed limestone. The porosity of the model was 40% and per- meability was 285 milliDarg. The production system consisted of a shut-in valve and a graduated cylinder for the collection of sam- pies.

Experimental conditions. The microorganism used in the experi- ments was Clostridium acetobutylicum (DSM-792). The optimal survival temperature is 38 ° C. The feeding medium (nutrient) con- sisted of 10% molasses in water.

Experimental procedure. The procedure followed for each micro- bial run was as follows. The model was packed completely with crushed limestone, and a vacuum was applied for 1.5-2 h. After this operation, brine with 18000 ppm NaCI and then oil was in- jected into the model. The microbial suspension was placed into a previously sterilized glass container and the suspension was in- jected into the model immediately. Then, the inlet and the outlet of the model were closed, and the shut-in period started. After the shut-in period, waterflooding was performed and 2000 cm 3 of dis- tilled water was injected into the model at a rate of 400 cm3/min. At every 30 min a sample was taken.

834

k

Graduated glass containers

i____.J' Pressure readout

"=- - - ~ - ~ - [ - - - - 1 , ,,

® / / ' ~ /~ \ \

®

/ / ~ \ ~ (~ / / ~ \ I .

i .-" , / \\ I T ~ ~ . " .' ! \ I ~ A ~ ~ ~-~/ / ~ k I

' ~ ~ ~ / / , ' l ', I ~ ~- ~- ~- ~-~-~--~--n- ~- ~

- ~ge ~

~ ~ heater

ISCO pump

,, ~ " ~ 0 [ I in ject ion z/k,....._.~ pu m p

(~® I. Pressure gauges

2. Manual valves

3. Pressure transducers

4, Reservoir model

Pressure readout F - - ~ - ~

B a c k - pressure

Samplel [ t l ine ~

5. Thermocouples 6. Temperature scanner 7. Temperature cont ro l le r

8. Vacuum line

Fig. 1. Experimental equipment for microbial enhanced oil recovery

Table 1. Experimental conditions and re- suits Experiment

code Concentration of bacterium in microbial suspension (%)

Shut-in period (h)

Oil recovery (oil production/ OOIP)

RR-1 -- -- 0.341 RM-I 25 45.0 0.456 RM-II 33 45.5 0.460 RM-III 50 46.0 0.454 RM-IV 100 45.0 0.465 RM-V 100 102.5 0.441 RM-VI 33 45.5 0.447

OOIP, original oil in place

Produced oil viscosity (cp)

1096 722 816 961 862

1438 856

Measurements. For the experiments, the following measurements were made: (i) total oil recovery; (ii) density, by density meter; (iii) oil viscosity, by I.C.I. (Middlesex, England) cone-and-plate viscometer; (iv) pH of water, by Fisher (Pittsburg, Penn., USA) pH meter; (v) surface tension of oil, by Karl Kolb (Dreieich, FRG) 2000 surface tensiometer.

Results and discussion

The results ob ta ined by the measurements men t ioned were evaluated. The results o f all microbia l experi- ments were c o m p a r e d with those o f reference experi-

ment RR-1 (Table 1). RM-VI was a straight repeti t ion o f R M - I I , and was pe r fo rmed in order to test the repro- ducibil i ty o f the microbial runs. It must be men t ioned that only the viscosity o f the first sample is taken into the cons idera t ion due to the presence o f emuls ion in the rest o f the samples.

Variation of microbial concentration

F r o m Table 1 it can be seen that there was a significant increase in oil recovery in microbial exper iments when c o m p a r e d to RR-1 [12% original oil in place (OOIP)].

835

Nevertheless, there is no indication that the concentra- tion of the microbial suspension (inoculum) affected the amount of oil recovered.

No important density variation between the refer- ence and microbial experiments was observed. Table 1 shows that, although the viscosities of the first four mi- crobial experiments Were obviously less than the viscos- ity of oil in RR-1, a coherent linkage between the amount of viscosity reduction and microbial concentra- tion cannot be derived.

The pH results obtained (not shown) indicated that the medium had become more basic in the first four mi- crobial experiments when compared to RR-1 but after a certain sample, the pH began to drop until it stabilized towards the last samples in these experiments. Again, it seems as if microbial concentration variation did not affect pH variation.

The same trend was observed in the oil surface ten- sion results. It is evident that this microbial treatment had no effect on the surface tension of the oil.

Variation of shut-in period

were less than that of RR-1, for RM-V (the experiment having a longer shut-in period) a substantial increase in oil viscosity occurred, the reason for which cannot be explained. This also contradicts the fact that oil recov- ery in this experiment increased compared to RR-1.

Another interesting result was obtained from pH the measurements. For RM-V it was observed that the me- dium had become acidic. Therefore, microbial acidifi- cation may be a compensating mechanism for oil re- lease, although the oil viscosity increased.

We conclude that C. acetobutylicum can be used for MEOR of Raman oil in a water flood. The increase in oil production was about 12% OOIP. Within the range studied, the variation in microbial concentration was insignificant with respect to oil recovery. This variation also seemed to have no effect on the type of recovery mechanism. The duration of shut-in period affected the type of recovery mechanism. This, however, requires further research. In successful microbial experiments, the main mechanism of recovery enhancement was found to be gas production. This gas dissolved in the oil and reduced its viscosity.

The increase in oil recovery in RM-IV and RM-V was nearly the same. Thus it can be stated that increasing the shut-in period, within the range studied, had no sig- nificant effect on the improvement in oil recovery.

From density measurements, almost no difference was observed except for some small shifts. This implies that the "hydrocarbon splitting" mechanism does not occur with C. acetobutylicum.

An interesting trend can be observed when Table 1 is examined for oil viscosity. Although the viscosities of oil produced in the first four microbial experiments

References

Donaldson EC, Clark JB (1982) Conference focuses on microbial enhancement of oil recovery. Oil Gas J 80:47-52

Jack TIL Thompson BG (1980) Patents employing microorgan- isms in oil production. In: Zajic JE, Cooper DE, Jack TR, Kasaric N (eds) Microbial enhanced oil recovery. Penn Well Books, Tulsa, Okla., USA, pp 19-24

Jack TR, Lee E, Mueller J (1985) Anaerobic gas production from crude oil. Int Bioresources J 1:167-185

Knabe S (1984) Overview of microbial enhanced oil recovery Oil Gas J 82:59-60