International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
ISSN 2319 - 4847
Modeling the Effects of Microbes in a Reservoir
Undergoing Microbial Enhanced Oil Recovery
Nmegbu, Chukwuma Godwin Jacob 1, Akpa G. Jackson2
1
2
Department of Petroleum Engineering, Rivers State University of Science and Technology,
Rivers State, Nigeria
Department of Chemical/Petrochemical Engineering, Rivers State University of Science and Technology,
Rivers State, Nigeria
Abstract
The need to maximize oil production from petroleum reservoirs has prompted the evaluation of several recovery techniques in the
oil and gas industry. The primary energy of a reservoir can only account for about 20 – 40% of the initial oil in place, leaving
quite a significant volume still residual in the reservoir. Microbial enhanced oil recovery is a tertiary recovery technique utilizing
the potential of certain microbes to significantly influence oil production from the reservoir with different mechanisms of
recovery. This study focuses on investigating oil recovery by increasing its mobility due to viscosity reduction as a result of
dissolved biogenic gases produced during microbe-oil reaction. Results showed that viscosity of a crude sample initially at 27cp
reduced to about 0.002cp as a result of the soluble biogenic gases produced by the microbe. A significant increase in the oil
permeability and cumulative oil production due to a reduced viscosity was also recorded.
Keywords: MEOR, Microbes, Solubility, Viscosity
1. INTRODUCTION
In 1926, Backman pioneered the discovery that certain microbes when grown in the presence of nutrients could free oil
from saturated porous media. Zobell whose experiment demonstrated the release of oil sand by certain sulfate reducing
bacteria, continued the work Beckman. He concluded that for microbes to degrade oil, certain metabolites must the
produced to alter the reservoir oil properties [1], [2]. Modeling the effects of microbes in a reservoir undergoing
microbial Enhanced Oil Recovery entails the development of a working mathematical presentation to analyze and
evaluate specified or the general recovery mechanisms of the microbes in a reservoir, having a comprehensive
mathematical interpretation for determining the incremental oil Recovery from MEOR application [3]. For a MEOR
program, microbes are selected, cultured and injected into the reservoir as an alternative tertiary oil recovery technology
[4]. These microbes interact with the hydrocarbon in the reservoir to produce microbial metabolites such as; biopolymers,
biogases, bioacids, solvents, etc which reduces the interfacial tension, plug off area of high permeable zones, re-pressurize
the reservoir, which ultimately helps to improve the recovery of heavy or residual crude oil from depleted and marginal
reservoirs and extending the life of the field [1], [2], [3], [5].
In the past, microbes were considered detrimental to the petroleum industry, it is now ascertained that they are beneficial
in oil recovery [1], [4], [5], [6]. Petroleum and gas industry operators are currently in the quest for the investigation of
various means of maximizing the production of oil from reservoirs so as to cope with the increasing demands of energy
[7], [8]. According to oil and gas researchers, conventional oil production technologies are able to recover only about one
third of the oil originally in place (OOIP). In the United States of American, it is estimated that over 300 billion barrels of
oil remain un-recovered after conventional technologies reached their economic limit, inexpensive, new technologies and
expertise to recover this significant volume of residual oil are often unavailable and as such threatens the recovery from
these reserves [8]. Microbial enhanced oil recovery involves the application of microbes and or the exploration of
microbial metabolic processes and products to increase production of residual or heavy oil from reservoirs. Microbes
degrades the hydrocarbon by breaking the hydrogen into smaller molecules, thereby increasing its mobility as a result of
reduction in viscosity. This study focuses of the effects of oil-dissolved biogenic gases produced by the microbes in the
reservoir after microbial-oil interaction for viscosity reduction and improved heavy crude mobility.
2. METHODOLOGY
2.1 Choice of microbes
The production of biogenic gases creates a free gas phase that can account for incremental oil Recovery in MEOR process
either by reduction of the oil viscosity when these produced gases go into solution or by re-pressurization of the reservoir
causing displacement from trapped capillaries and enhancing mobilization of oil to the producing wells. Gas producing
microbes are; clostridium, Desulfovibrio, Pseudomonas, and methanogens. Their morphologies confirm their ability to
produce bio acids and a higher proportion of biogases. Carbon dioxide, hydrogen, methane and nitrogen are some of these
Volume 3, Issue 6, June 2014
Page 206
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
ISSN 2319 - 4847
gases evolved after the microbe-oil reaction. For this study, pseudomonas proved suitable for the investigation used on the
basis of its ability to produce quite a significant percentage of biogases with a negligible percentage of other metabolites.
2.2 Biochemical reactions of microbes
The biochemical reactions leading to improving heavy residual oil recovery are intricate and proceeds via multiple inter
and intra-molecular reactions involving de-polymerization, desulfurization, de-nitrification, and de-metalation pathways.
2.3 Derivation of solution biogenic gas model during MEOR
The purpose of this study is aimed at determining the fluid properties that are affected by certain metabolites. These
properties are then incorporated in the production equation to obtain the required model for residual or heavy oil
production using microbes.
Accounting for volume of produced biogenic gas;
Vg(P,T)MA = Volume of gas dispersed due to microbial Activities.
VL(P,T)MA = Volume of oil due to microbial Activities.
V*(P,T)MA = Volume of dispersed biogenic gas which evolved during biochemical reaction between the reservoir and
microorganisms.
MA = Microbial activity.
When P and T are dropped to Pref and T ref.
When assumed that only a mixture of liquid and dispersed gas exist and that the dispersed gas enters only through the
volume fraction (Vf)MA.
 Vg 
(1)

V FMA  
V V 
g  MA
 L
V gMA

 V fVL

1  VL


 MA
(2)
VFMA = volume fraction of the dispersed biogenic gas due to microbial activities
VgMA = volume of biogenic gas due to microbial activities
VLMA = volume of liquid due to microbial activities
(3)
The dispersed biogas fraction (Vf) from a solution of dissolved biogas in oil at any P and T is then determine by
 V* 

RSmA  
 VL P, T   MA
(4)
where RS  biogenic gas solubility
but
P  Pr ef  Yˆ T RS
(5)
Where
(4)
dp
ˆ 
dvˆ
(6)
And
Pref is a small pressure at which a negligible amount of gas is dissolved in the oil.
To determine the relationship between P and (Vf)mA at equilibrium, it is paramount to note that mass of gas is constant
and independent of P and T.
Thus:
M mA  Mg P, T   Mc P, T MA
Where
(7)
M mA  Total mass of gas in the reservoir due to M
M
g
 Mass of gas evolved due to M
A
A
M c  Mass of condensed gas due to M A
Since, mass of condensed biogas (Mc) is constant when it is vaporized and also assuming that this Vapor is a perfect gas.
the EOS can be applied.
Thus:
Volume 3, Issue 6, June 2014
Page 207
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
ISSN 2319 - 4847
Pv MA  nRT MA
But
n
(8)
m
M
(7)
 MRTref 
: .Pr efV MA  

 M
 MA
(9)
 PV * 

M cmA  
 Rg Tref  MA
Similarly
 PVg 
M gmA  

 RT  MA
Combining the equations above
(10)
(11)
 PV 
 Pr efV * 

M mA   g   
RT

 MA  R Tref  MA
Also combining the above
 PV
M mA   g
 RT
(12)
 Pr ef  P  Pr ef  

  

VLb 
ˆ
  MA
 MA  RTref 
(13)
Where M mA is the total mass of biogas dissolved in the oil at bubble point
Setting R = Rsb when Vg=0
From Pb -Pref = ˆ T Rsb
Where
Rsb  gas solubility at bubble point.
Since evaluation is taken at bubble point ,
 Pr ef

 V *  and
M MA  
VLb 

Rsb MA  
 RTref

 VLb  mA
Eliminating average biogas solubility
(14)
 Pr ef   Pb  Pr ef  
M MA  
VLb 

 RTref    T  
(15)
Simplifying we have
 Tref P
 P  Pr ef
Vg  



 T Pr ef
 P  Pr ef
 
VL  b

  mA 
 
VLb  mA
 
(16)
Due to gas evolution, volume of oil changes and its compressibility is small
VL ~
 VLb
Where
VLb is the volume of oil at bubble point (Pb)
The terms proportional to Pref in equation (16)above subtracts out and replacing Vg with
  Vf
 B g 
  1  V f

   Pb  P 



 MA  P  MA
T

BgmA   ref ,
 T Pr ef


 MA
V f VL
1V f
gives:
(17)
(18)
At this point, we assume that variation of temperature is small on an absolute scale
Thus the ratio
T
is slightly greater than one
Tref
Volume 3, Issue 6, June 2014
Page 208
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
ISSN 2319 - 4847
From 18,
ˆ T MA 
P  Pr ef
R sb
(19)
MA
Substituting equation (19) into equation (18) yield
Tref Pb  Pr ef 
T Pr ef R sb MA
Bg MA 
(20)
But Pb  Pref in many practical situations therefore;
P b 
Tref
T Pr ef R sb
Bg MA 
(21)
MA
Where Bg is the solubility parameter of the reservoir due to microbial activities.
When Vf and P satisfying 17 above vary at different point,
Then,
PMA 
 P 2
Pb 1  V f 
2
(22)
V f
MA
Recall that by Darcy’s Law in a MEOR Process
U MA  P 
(23)
Where
K
(24)
mA   
   mA
Substitute equation (24) and (23) into (22) to obtain
  K  P 2

(25)
U MA  
V f 
2
  Pb 1  V f 
 MA
The gas solubility during the microbial activities in the reservoir helps to reduce interfacial Tension and Viscosity. The
evolved gas phase in the reservoir forms a gas cap, maintaining the pressure of the reservoir and preventing fast depletion
of reservoir energy, thus sustaining production for a longer period.
MEOR processes generate gases which dissolve and reduce the strength of the capillary and viscous forces which exist
fluid/fluid and fluid/rock interface. Depending on concentration of the biogases in the crude, two types of gas saturation
exist; namely sub-saturation and super-saturation.
Sub-saturation: Occurs when not enough biogas is available to dissolve in order to satisfy thermodynamic equilibrium at
prevailing reservoir pressure and temperature.
Super-saturation: This corresponds to having more biogases dissolved than there should be under thermodynamic
equilibrium. It occurs when the oil cannot evolve gas fast enough to keep up with the depressurization.
A bubble which might f0rm in the crude oil by the vaporization of dissolved gas at supersaturated condition can expressed
by;
2
PVap .  P 
R
(26)
Where  is the interfacial tension
From the above, interfacial Tension can be obtained as:
 PVap  P 
 MA   R

2

 MA
(27)
Considering that the average liquid and gas velocities are equal, the mixture velocity is given by:
U mixt . MA  U L   U g  MA
(28)
U L MA  1  Vf U L ma
(29)




U g MA  V f U g


ma
(30)
Where, UL and Ug are superficial velocities of the oil and gas respectively.
The mixture density
 mixt = V is given as:
f
Volume 3, Issue 6, June 2014
Page 209
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
~  L 1  V f
 mixt  V f    g V f    L 1  V f  

ISSN 2319 - 4847
(31)
The crude oil mass average velocity (Um) is given as:

  L 1  V f uL   gV f U g
UmMA  
 V f 




(32)
The equation expressing the conservation of mass of each of the two phases is:
  L
1  V f    L 1  V f U L   O

t

 MA
(33)
And
   g Vf

   gV f U g   O

t

 MA
(34)
Where,
UL and Ug are the average gas and Liquid velocity, respectively.
When
U L  U g.
U m  U  UL  Ug
(35)
Incorporating the permeability of oil and biogas into the above, we have:

U LmA  1  V f U L

MA
 KK rL 
K
 
  
p
 L V f 
 L
 mA
 KK rg



K
U gmA  V f U g mA   
P    
p 
 mA   g V f  
  g
(36)
(37)
Where:
g
= Molecular velocity of gas.
 L = Molecular velocity of Liquid.
The ratio of relative permeability is:
 KL 
 L Mg V f 
1  V f  L 
  

 

 K g  mA   g  L V f   MA  V f  g  MA
(38)
From equation above, the effective viscosity (µ) of liquid and gas can be determined as;
 
 LmA   L 
 K L  MA
 
 gmA   2 
K 
 g  MA
 misxt mA   L   g 
(39)
(40)
(41)
Considering oil production after microbial action in-situ, Oil production rate can be treated as a function of the drawdown
pressure. Assuming: A = Cross-section area of the reservoir undergoing MEOR.
U = Mixture Velocity as given by Darcy’s law.
A.U = Volume flow rate of the oil and gas mixture, which is greater than the volume flow rate,
 L 1  V f 
.
The mass flow rate of oil:
 L Q mA    L A 1  V f  V f dp 
dx  MA

(42)

 
The cumulative production is obtained as the integral over time of the rate of production.
 LQ (t )   L  to Q (t ) dt
Volume 3, Issue 6, June 2014
(43)
Page 210
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
Q  A  1  V f 
ISSN 2319 - 4847
dp
dx
(44)
Where

KL
L
(45)
 K
dp 
Therefore, QMA   A L 1  V f  

dx  MA

L
(46)
The model can be used to show how the reservoir fluid properties have been altered, implying an increased flow.
Reservoir fluid properties that can be determined from the above derived mathematical model are thus;
The permeability of oil as a result of microbial activities can be obtained from;
KL 
 1  V f   L 
  


 K g  mA  V f  g  MA
(47)
Then

1  V f   L 
(48)
K L mA   K g

V f  g 

MA
Viscosity (µ) of oil as a result of biogas dissolution after microbial actions can be determined from as
 g 
 

 LmA   L  And g mA  
 Kg 
 K L  MA

 MA
 mixt
mA
  L   g MA
Solubility due to microbial activities can be calculated from;
Tref 1 dp
Bg MA 
T Pr ef dx MA
The cumulative production of a reservoir undergoing MEOR process can also be obtained from
 K
dp 
QMA   A L 1  V f

dx  MA
 L


Some
TheAssumptions
reservoir is assumed
made to be related to PVT cell.
 The thermodynamics of fluids are independent of the wall properties of the reservoir, and provided that these walls are
not so closely spaced as to affect the thermodynamics properties of the bulk fluid.
 Mass of the dissolved gas released considered.
 Gas flow is in 1 dimension, from the point of injection to the reservoir extent.
 Metabolite production mostly biogenic gases.
 Gas solubility considered
3. RESULTS AND DISCUSSION
Table 1: Field parameters for model validation
L
cp 
 g cp 
Kg
md 
Vf
Po
Psi 
1.100
0.0250
0.001
0.8
3,600
1.105
0.0234
0.004
0.7
3,200
1.114
0.0220
0.033
0.6
30,000
1.123
0.0217
0.102
0.5
2800
1.196
0.0201
0.222
0.4
2400
1.337
0.0184
0.395
0.3
2200
1.497
0.0139
0.614
0.2
800
2.100
0.0128
0.867
0.1
400
The calculations of the general effect of microbial activities on these parameters are shown below:
Given; A=600ft2 ,  L  1.100,  g  0.250, V f  0.8, K rg  0.004, then,
T
 C
0
50
70
80
90
110
130
150
180
Permeability of gas in oil after microbial application can be obtained from
Volume 3, Issue 6, June 2014
Page 211
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
 1  V f
KL 

  
 K g  mA  V f
ISSN 2319 - 4847
 L 
 
 
 g  MA
 1Vf   
 L
K L mA   K g 
  V f   g  MA

 1  0.8  1.100 
K L mA  0.004


 0.8  0.0250

 0.2  1.100
 0.004

 0.8  0.0250
 0.004(0.2544)  0.0044 mD
For oil viscosity is given as
 
 L  mA    L 
 K L  MA
 1.100 
 L mA   

 0.044  MA
 L mA   25.0cp
The oil viscosity due to microbial application is calculated as:
Solubility of gas in oil due to MEOR activities is calculated from equation (23) above as;
Tref 1 dp but recall,
Bg   
MA
T Pr ef dx MA
Pr ef  15.6 0 C and P  14.7 PSia
Bg  0.83
 1  V f
 K g 
  V f
L 
 
 
 g  mA
 1  0.7 
 0.004

 0.7 
1.105
0.0234
KL
 0.004 0.4287 47.2
K L  mA    0.081md
The oil viscosity due to microbial application is calculated as:
Volume 3, Issue 6, June 2014
Page 212
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
ISSN 2319 - 4847
 
  L 
 K L  mA
L  mA 
 1.105 
 

 0.081 
: . L mA  13.64cp
Solubility of gas in oil after microbial activities is;
Tref 1 dp
Bg   
MA
T Pr ef dx MA
Bg 

Bg 
MA


15.6 1 dp
70 14.7 dv
15.6
ln 14.7
70
MA

 0.599 MA
 K
dp 
Q mA    A L 1  V f  

dx  mA 

L
0.081 1  0.7
Q mA  
600
Q mA  
0.15 bbl / Day
13.64
Table 2: Deduced parameters after MEOR application
L Cp 
Q bbl / day 
Krl md 
27.500
13.600
1.000
0.210
0.060
0.020
0.006
0.002
0.018
0.15
38.8
1121.5
19345
279000
8540000
196000000
0.044
0.084
1.144
5.280
19.800
55.970
264.500
1280.000
Fig 1 Plot of cumulative production against oil viscosity
Volume 3, Issue 6, June 2014
Page 213
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
ISSN 2319 - 4847
Fig 2 Plot of cumulative production against oil viscosity in 3-dimensions
Fig 3 Plot of cumulative production against permeability of mobilized oil
Fig 4 Plot of cumulative production against permeability of mobilized oil
Fig 5 Plot of oil viscosity against effective permeability of mobilized oil
Volume 3, Issue 6, June 2014
Page 214
International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 6, June 2014
ISSN 2319 - 4847
Figure 1 and 2 shows the plot of cumulative production against the altered viscosity of oil. The plot shows that as the
viscosity of crude oil decreases, cumulative production increases. This improved production is traceable mechanism of
improved mobility of oil as a result of the dissolved biogenic gases in the oil. On the other hand, if more gases are evolved
from the oil, the oil becomes more viscous resulting to a reduction in cumulative production. The Crude becomes very
heavy at this point and is difficult to produce.
Figure 3 and 4 shows the relationship between cumulative production and oil permeability. The plot shows that
production of oil increases with an increased permeability of oil in the microbe-subjected reservoir. Injected microbes tend
to plug thief zones, diverting flow towards the production points in the reservoir, plugging these high permeable zones in
the reservoir increases sweep efficiency during production. Permeability of a rock is the measure to which the rock can
transmit fluid through itself. Once oil viscosity drops in magnitude, the permeability of the oil in the reservoir increases
instantly. The inverse relationship between viscosity and permeability is shown in figure 5.
4. CONCLUSION
Microbial enhanced oil recovery still remains the cheapest, environmental friendly tertiary recovery technique
incorporating several mechanisms to alter certain rock and fluid properties to enhance oil flow to the surface. Before these
microbes can be utilized, thorough investigation must be done to ascertain mechanism of recovery of the selected microbe.
Pseudomonas was used for this investigation on the basis of its ability to produce biogases that will dissolve in heavy
crude to reduce its viscosity and increase its mobility. This research is limited to the assumption that no in-situ gas was
present, it is highly recommended that further study be done to ascertain the effects of in-situ gases on the produced
biogases by the microbe.
Acknowledgement
The authors are grateful to Wosu Angus and Pepple Daniel Dasigha for their immense contributions to this work.
References
[1] C.E ZoBell, (1946) bacteriological processes for treatment of fluid bearing earth formation. US patent No. 2,
413,278.
[2] C.E.. ZoBell, Bacterial release of oil from oil bearing materials, Part I, World Oil, 126(13), pp. 1-11.
[3] M.M Chang, F. Chung, R. Bryant, H. Gao, and T. Burchfield (1991): Modeling and laboratory investigation of
microbial transport phenomena in porous media. In: SPE 22845 presented at 66th Annual Technical Conference and
exhibition of SPE in Dallas Texas.
[4] T. A. Ryan T. 2012, “Microbial Enhanced Oil Recovery: A Pore‐Scale Investigation of Interfacial Interactions”, a
dissertation for the degree of doctor of philosophy in chemical engineering; pp. 1-2.
[5] V. Moses: MEOR in the field: Why so little?, proceedings from the 1990 International Conference on Microbial
Enhancement of Oil recovery, reprinted from: Microbial Enhancement of Oil Recovery Recent Advances, edited by
E.C. Donaldson, Elsevier Science Publishers, 1991, p 21-28.
[6] N Youssef, . S. Elshahed, and M. J. McInerney (2009), Microbial processes in oil fields: culprits, problems, and
opportunities, Advances in applied Microbiology, vol. 66, edited,pp. 141‐251, Elsevier Academic Press Inc., San
Diego.
[7] S. A. Kianipey (1990), Mechanisms of oil displacement by microorganisms. Microbial Enhancement of Oil Recovery
– Recent Advances, ed. E.C. Donalsdon, Amsterdam: Elservier Science Publishers.
[8] S. L. Donaldson and P. L Thomas: “Reservoir Engineering Analysis of Microbial Enhanced Oil Recovery.” SPE
Paper 63229, Presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, 1st October, 2000.
[9] J. Costerton, D. Lewandowski, D, Caldwell, D. Korber and H. Lappin‐Scott, (1995), Microbial biofilms, Annual
Review Microbiology, 49, 711‐745.
[10] S. C. Lin, S. C Minton, , M. M., Sharmaand and G. Georgiou, (1994), Structural and immunological
characterization of the biosurfactant produced by Bacillus‐licheniformis JF‐ 2, Applied and Environmental
Microbiology, 60(1), 31‐38.
[11] R. M Gray, A Yeung., M. J Foght, and W. H. Yarranton, (2008), Potential microbial enhanced Oil Recovery
Processes: a critical analysis, Society of Petroleum Engineers AnnualTechnical Conference and Exhibition, SPE
114676, Denver, Colorado, 21‐24 September.
[12] H. K Suthar,. A. Hingurao, and A. Nerurkar (2008), Evaluation of bio-emulsifier mediated microbial enhanced oil
recovery using sand pack column. Journal of Microbiological Methods, 75, 225‐230.
Volume 3, Issue 6, June 2014
Page 215