Note: Descriptions are shown in the official language in which they were submitted.
= PF 71956 CA 02823752 2013-07-03
Multistage process for producing mineral oil using microorganisms
The present invention relates to a multistage process for producing mineral
oil from mineral oil
deposits by injecting aqueous flooding media into a mineral oil formation
through injection
boreholes and withdrawing the mineral oil through production boreholes, in
which the mineral oil
yield is increased by the use of microorganisms in combination with measures
for blocking
highly permeable zones of the mineral oil formation.
In natural mineral oil deposits, mineral oil occurs in cavities of porous
reservoir rocks which are
closed off from the surface of the earth by impervious covering layers. In
addition to mineral oil,
including proportions of natural gas, a deposit further comprises water with a
higher or lower
salt content. The cavities may be very fine cavities, capillaries, pores or
the like, for example
those having a diameter of only approx. 1 m; the formation may additionally
also have regions
with pores of greater diameter and/or natural fractures.
After the borehole has been sunk into the oil-bearing strata, the oil at first
flows to the
production boreholes owing to the natural deposit pressure, and erupts from
the surface of the
earth. This phase of mineral oil production is referred to by the person
skilled in the art as
primary production. In the case of poor deposit conditions, for example a high
oil viscosity,
rapidly declining deposit pressure or high flow resistances in the oil-bearing
strata, eruptive
production rapidly ceases. With primary production, it is possible on average
to extract only 2 to
10% of the oil originally present in the deposit. In the case of higher-
viscosity mineral oils,
eruptive production is generally completely impossible.
In order to enhance the yield, what are known as secondary production
processes are therefore
used.
The most commonly used process in secondary mineral oil production is water
flooding. This
involves injecting water through injection boreholes into the oil-bearing
strata. This artificially
increases the deposit pressure and forces the oil out of the injection
boreholes to the production
boreholes. By means of water flooding, it is possible to substantially
increase the yield level
under particular conditions.
In the ideal case of water flooding, a water front proceeding from the
injection borehole should
force the oil homogeneously over the entire mineral oil formation to the
production borehole. In
practice, a mineral oil formation, however, has regions with different levels
of flow resistance. In
addition to oil-saturated reservoir rocks which have fine porosity and a high
flow resistance for
water, there also exist regions with low flow resistance for water, for
example natural or
synthetic fractures or very permeable regions in the reservoir rock. Such
permeable regions
may also be regions from which oil has already been recovered. In the course
of water flooding,
the flooding water injected naturally flows principally through flow paths
with low flow resistance
from the injection borehole to the production borehole. The consequences of
this are that the
PF 71956 CA 02823752 2013-07-03
2
oil-saturated deposit regions with fine porosity and high flow resistance are
not flooded, and that
increasingly more water and less mineral oil is produced via the production
borehole. In this
context, the person skilled in the art refers to "watering out of production".
The effects
mentioned are particularly marked in the case of heavy or viscous mineral
oils. The higher the
mineral oil viscosity, the more probable is rapid watering out of production.
The prior art therefore discloses measures for closing such highly permeable
zones between
injection boreholes and production boreholes by means of suitable measures. As
a result of
these, highly permeable zones with low flow resistance are blocked and the
flooding water is
forced to flow again through the oil-saturated, low-permeability strata. Such
measures are also
known as "conformance control" measures. An overview of measures for
conformance control is
given by Boiling et al "Pushing out the oil with Conformance Control" in
Oilfield Review (1994),
pages 44 if
For conformance control, it is possible to use comparatively low-viscosity
formulations of
particular chemical substances which can be injected easily into the
formation, and the viscosity
of which rises significantly only after injection into the formation under the
conditions which exist
in the formation. To enhance the viscosity, such formulations comprise
suitable inorganic or
organic, or polymeric, components. The rise in viscosity of the injected
formulation can firstly
occur with a simple time delay. However, there are also known formulations in
which the rise in
viscosity is triggered essentially by the temperature rise when the injected
formulation is
gradually heated to the deposit temperature in the deposit. Formulations whose
viscosity rises
only under formation conditions are known, for example, as "thermogels" or
"delayed gelling
systems".
SU 1 654 554 Al discloses mixtures of aluminum chloride or aluminum nitrate,
urea and water,
which are injected into the mineral oil formation. At the elevated
temperatures in the formation,
the urea is hydrolyzed to carbon dioxide and ammonia. The release of the
ammonia base
significantly increases the pH of the water, and results in precipitation of a
highly viscous
aluminum hydroxide gel, which blocks the highly permeable zones.
US 4,889,563 discloses the use of aqueous solutions of aluminum hydroxide
chloride in
combination with urea or hexamethylenetetramine (urotropin) for blocking of
underground
mineral oil formations. Here too, the hydrolysis of urea or
hexamethylenetetramine in the
formation leads to an increase in the pH and the precipitation of aluminum
hydroxide.
US 4,844,168 discloses a process for blocking sections of high-temperature
mineral oil
formations, in which polyacrylamide and a polyvalent metal ion, for example
Fe(III), AI(III), Cr(III)
or Zr (IV), are injected into a mineral oil formation with a reservoir
temperature of at least 60 C.
Under the conditions in the formation, some of the amide groups -CONH2 are
hydrolyzed to
-COOH groups, and the metal ions crosslink the -COOH groups formed, such that
a gel is
formed with a certain time delay.
PF 71956 CA 02823752 2013-07-03
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Further suitable mixtures for "Conformance Control" are disclosed, for
example, by RU 2 066
743 Cl, WO 2007/135617, US 7,273,101 B2, US 6,838,417 B2 or US 2008/0035344
Al.
It is additionally known that the mineral oil yield can be enhanced by the use
of suitable
chemicals as assistants for oil production. With the aid of these measures,
the mobility of the
mineral oil in the formation should be increased, such that it can be forced
out of the formation
more easily in the course of water flooding. This phase of mineral oil
production is frequently
referred to as "Tertiary Oil Production" or "Enhanced Oil Recovery" (EOR). For
example, the
interfacial tension a between the mineral oil and the aqueous phase can be
lowered for this
purpose by the addition of suitable surfactants, thus increasing the mobility
of the oil phase.
This technique is also known as "surfactant flooding". An overview of
techniques for tertiary oil
production can be found, for example, in the Journal of Petroleum Science and
Engineering 19
(1998) 265-280.
One known technique for tertiary mineral oil production is to enhance the
mineral oil yield by
using microorganisms, especially bacteria. This technique is known as
"Microbial Enhanced Oil
Recovery" (MEOR). This involves either injecting suitable microorganisms,
nutrients for the
microorganisms and optionally oxygen into the mineral oil formation, or
promoting the growth of
microorganisms already present in the mineral oil formation by injecting
nutrients and optionally
oxygen.
There are various known mechanisms by which bacteria can increase the mobility
of mineral oil,
for example by the formation of surfactants, the formation of polymeric
substances and the
resulting increase in viscosity of the aqueous phase, the formation of
biofilms and the
associated cross-sectional constriction of pores up to and including complete
blockage (change
in the flow paths), reduction in the viscosity of the mineral oil resulting
from degradation of high
molecular weight hydrocarbons, formation of gases (e.g. CO2 or CI-14),
formation of organic
acids which can attack the rock formation and hence create new flow paths, or
resulting from
the detachment of the mineral oil from the rock surface. Methods for MEOR and
microorganisms suitable for this purpose are disclosed, for example, in US
4,475,590, US
4,905,761 or US 6,758,270 B1.
RU 2 060 371 Cl discloses a process for producing mineral oil using
microorganisms from a
deposit with inhomogeneous permeability, which has at least one injection
borehole and at least
one production borehole. In the process described, the deposit pressure is
periodically
increased and lowered. In pressure increase phases, microorganisms present in
the mineral oil
formation are activated by injecting a nutrient solution into the mineral oil
formation.
Subsequently, the injection borehole is closed. The withdrawal of mineral oil
or water mixtures
through the production borehole reduces the pressure again.
PF 71956 CA 02823752 2013-07-03
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RU 2 194 849 Cl discloses a process for extracting mineral oil using
microorganisms from a
deposit with inhomogeneous permeability, which has at least one injection
borehole and at least
one production borehole. In the process described, the deposit pressure is
periodically
increased and reduced. In pressure increase phases, microorganisms and
nutrient solution are
injected into the formation in each case through the injection and production
boreholes; in
pressure reduction phases, the injection borehole is closed and liquid is
withdrawn from the
formation through the production borehole. Preference is given to injecting
mesophilic bacteria
into the injection borehole, and thermophilic bacteria into the production
borehole. A
disadvantage of this process is the low efficiency since the production
borehole does not
constantly produce oil but is regularly shut down.
RU 2 204 014 Cl discloses a process for producing mineral oil, in which a
nutrient solution and
carbon-oxidizing bacteria are injected into a mineral oil formation, followed
by a
biotechnologically produced polyacrylamide together with a crosslinker.
Mineral oil formations frequently do not have a homogeneous temperature
distribution, but
rather have more or less significant temperature gradients. Such temperature
gradients may be
of natural origin, but they can especially be caused by measures for secondary
and/or tertiary
mineral oil production. In the case of water flooding, cold water is
frequently injected into the
formation for months or even years. This generally lowers the formation
temperature to a
greater or lesser degree in the region around the injection borehole. As a
typical example, table
1 shows the temperature decline in the formation temperature for some deposits
in northern
Siberia after prolonged water flooding::
Deposit Formation temperature Formation Difference
[ C] temperature in the [ C]
injection region [ C]
51 90 45 45
S2 72 39 33
S3 78 37 41
S4 78 32 46
S5 101 56 45
S6 85 42 43
Table 1: Deposit temperatures of different Siberian deposits S1 to S6 after
prolonged water
flooding.
It was an object of the invention to provide a process for MEOR, which is
particularly suitable for
PF 71956 CA 02823752 2013-07-03
Accordingly, a process has been found for producing mineral oil from
underground mineral oil
deposits with deposit temperatures (TL) in the range from 25 C to 120 C, at
least one injection
borehole and at least one production borehole being sunk into the formation,
and mineral oil
being produced from the deposit, by injecting aqueous flooding media into the
at least one
5 injection borehole and producing mineral oil through the at least one
production borehole,
flooding water of temperature < 25 C being injected in a process step (0) such
that ¨ as a result
of the continued injection of the flooding water - the temperature of the
deposit at the site of the
injection borehole (T) is lowered compared to the original deposit temperature
11 and a
temperature gradient is built up between the injection borehole and the
production borehole with
the temperature Tp IL, and wherein the process additionally comprises ¨ in the
sequence
mentioned - at least the following steps in which the aqueous flooding media
mentioned below
are each injected into the formation through said at least one injection
borehole:
(I) mobilizing mineral oil in the formation by means of microorganisms by
(la) injecting at least one aqueous formulation of oil-mobilizing
microorganisms, an
aqueous nutrient solution and optionally an oxygen source, and/or
(lb) activating oil-mobilizing microorganisms already present in the formation
by
injecting an aqueous nutrient solution and optionally an oxygen source,
(II) injecting flooding water,
(III) blocking highly permeable regions of the formation,
(IV) injecting flooding water,
(V) mobilizing mineral oil in the formation by means of microorganisms by
repetition of
process step (I), and
(VI) injecting flooding water.
In a preferred embodiment of the invention, process step (III) is performed by
injecting at least
one aqueous, gel-forming formulation (9, said formulations (F) comprising
water and one or
more water-soluble or water-dispersible components which form high-viscosity
gels after
injection into the deposit under the influence of the deposit temperature and
hence completely
or partially close the highly permeable regions.
List of drawings:
Figure 1 Schematic diagram of water flooding.
PF 71956 CA 02823752 2013-07-03
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Figure 2 Schematic diagram of the formation after the injection of
microorganisms.
Figure 3 Schematic diagram of the closure of highly permeable
regions of the
formation by gels.
Figure 4 Schematic diagram of the formation of a new flood zone.
Figure 5 Schematic diagram of the formation after the injection of
microorganisms into the new flood zone.
Figure 6 Schematic diagram of the application of the process to a
deposit with
several production horizons.
With regard to the invention, the following can be stated specifically:
The process according to the invention is employed once primary mineral oil
production has
stopped due to the autogenous pressure of the deposit, and the pressure in the
deposit is
maintained by injection of liquid flooding media. It can be employed
advantageously especially
when even the injection of water leads only to unsatisfactory results.
Deposits
The mineral oil deposits may be deposits for all kinds of oil, for example
those for light or for
heavy oil, with the proviso that the deposit temperatures (TL) are in the
range from 25 C to
120 C, preferably 30 C to 110 C, more preferably 35 C to 105 C and, for
example, 40 C to
105 C. The deposit temperature means the naturally existing temperature in the
deposit. It can
be altered by the process steps described hereinafter.
The deposits have a heterogeneous permeability. This is understood to mean
that the
permeability is not the same in all regions of the deposit, but that the
deposit has zones of
higher and lower permeability.
Process
To execute the process, at least one production borehole and at least one
injection borehole are
sunk into the mineral oil deposit. In general, a deposit is provided with
several injection
boreholes and optionally with several production boreholes. Aqueous flooding
media can be
injected into the mineral oil deposit through the injection boreholes, and
mineral oil is withdrawn
from the deposit through the production boreholes. The aqueous flooding media
used in each of
the individual process steps are described hereinafter. According to the
invention, the aqueous
PF 71956 CA 02823752 2013-07-03
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flooding media are injected in the process steps described hereinafter always
using the same
injection boreholes; thus, no new injection boreholes are drilled. What is
important hereinafter is
not whether the terms "injection borehole" or "production borehole" are used
hereinafter in the
singular or plural, but what is meant in each case is "at least one injection
borehole" or "at least
one production borehole".
The term "mineral oil" here of course does not mean single-phase mineral oil,
but what is meant
is the customary emulsions which comprise oil and formation water and are
produced from
mineral oil deposits. The oil phase and the water phase are separated after
production in a
manner known in principle.
Process step (0)
The process according to the invention is employed in a deposit in which the
pressure is already
being maintained by injecting flooding water. This involves injecting flooding
water into the
injection borehole(s) and withdrawing mineral oil from the production
boreholes. This procedure
is also known as "water flooding". The flooding water used may be all kinds of
water, for
example fresh water, salt water or brine, and the water may optionally also
comprise further
additives. The water flooding may already have lasted for months or even
years. This process
step preceding process step (I) is referred to hereinafter as process step
(0).
Process step (0) alters the original conditions in the deposit.
As pressure is built up by the flooding water injected into the injection
borehole, the mineral oil
in the formation is forced in the direction of the production borehole,
naturally on the path of
least resistance. The mineral oil or the flooding water thus flows initially
through zones of
relatively high permeability.
Accordingly, in a zone thus formed in the region between the injection
borehole and the
production borehole, in which oil is displaced by water, while no mineral oil
is displaced from
other regions of the formation. This is shown schematically in figure 1. Water
is injected into the
injection borehole (1), flows from there in the direction of the production
borehole (2), and in the
process forces mineral oil out of the pores in the direction of the production
borehole. The flow
direction is indicated by the arrow (3). Within the (gray-shaded) zone (4),
mineral oil is at least
partly displaced by the water front
The direction of the water front (3) and the size and position of the zone (4)
are determined by
the circumstances in the deposit, for example the three-dimensional dynamics
of the
permeability characteristic, fissuring or local geological faults. The zone
(4) may have a
complicated branched form, especially when several injection boreholes for
water and several
production boreholes are present in this section.
PF 71956 CA 02823752 2013-07-03
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In the flow zone (4), the flooding water generally does not force the mineral
oil onward in a
homogeneous manner. The reason for this is that the permeability is generally
not
homogeneous in the flow zone either. When more porous regions are present, for
example fine
cracks, fractures or fissures, the water flows preferentially through these
zones of relatively low
flow resistance. Moreover, the oil under some circumstances is removed only
partially from
pores. For example, an oil droplet which is not entrained by the water flowing
through these
pores can remain in a pore. With increasing duration of water flooding,
preferential flow paths
for the water form can form to an ever greater degree. As a result of this,
ever more water
reaches the production borehole and, correspondingly, the proportion of water
in the oil-water
mixture produced increases with increasing duration of water flooding. This
effect is known to
the person skilled in the art as "watering out of production". Watering out of
production is
therefore a sign that the aqueous flooding medium is no longer flowing
homogeneously through
the formation from the injection borehole to the production borehole, but has
found preferred
flow paths through zones of greater than average permeability in the
formation. The flooding
water flowing through preferred flow paths no longer mobilizes any oil, or at
least mobilizes it
only insufficiently. Considerable amounts of oil can still remain in the flow
zone (4). Moreover,
further mineral oil still remains in the mineral oil formation outside the
zone (4),
The process according to the invention can be used particularly advantageously
when watering
out of production has already set in. It can especially be used when watering
out of production
has reached 70 to 80%.
The injection of flooding water additionally alters the temperature
distribution in the mineral oil
formation. This is because the flooding water used for injection is generally
comparatively cold.
It may, for example, be seawater. It therefore generally has a temperature of
less than 25 C,
preferably less than 20 C and frequently even distinctly lower.
As a consequence of the advanced injection of cold flooding water, the
temperature of the
deposit at the site of the injection borehole falls at first compared to the
original deposit
temperature TL. The temperature of the deposit at the site of the injection
borehole shall be
referred to hereinafter as Ti. The flow of the flooding water in the direction
of the production
borehole (i.e. of zone (4)) can also cool further regions of the flow zone. Of
course, the cooling
effect is at its greatest at the injection borehole and decreases with
increasing distance from the
production borehole.
In the flow zone (4) between the injection borehole (1) and the production
borehole (2), a
temperature gradient thus forms, with the temperature tending to rise in the
direction of the
production borehole, but - according to the flow conditions - not necessarily
homogeneously.
Accordingly, the temperature of the deposit at the injection borehole (Ti) is
lower than the
temperature of the deposit at the production borehole (Tp). According to the
conditions, Tp may
be equal to the deposit temperature TL, or else the production borehole may
already have been
PF 71956 CA 02823752 2013-07-03
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cooled somewhat by the influx of colder flooding water, in which case Tp TL.
The temperature
difference Tp - Ti is generally at least 5 C, preferably at least 10 C and
more preferably at least
20 C, and especially at least 30 C, for example 5 C to 60 C, preferably 10 C
to 55 C, more
preferably 15 C to 50 C.
Process step (I)
In process step (I), the mineral oil formation is treated with suitable
microorganisms.
In a first embodiment (la), the treatment can be effected by injecting
suitable microorganisms
into the deposit. In a second embodiment (lb), microorganisms already present
in the mineral oil
formation are activated. By means of both methods, further mineral oil in the
formation is
mobilized and the mineral oil yield is enhanced again. The mobilization is
effected essentially in
the region between the injection borehole and the production borehole which
has already been
partially exploited by process step (0) (zone (4) in figure 1), but it is
additionally also possible in
principle to cover further regions of the formation.
For preparation for process step (I), geophysical and biochemical studies of
the mineral oil
formation should appropriately first be carried out. Firstly, the temperature
distribution of the
mineral oil formation is determined, at least in the region between injection
borehole and
production borehole, and especially in the region of the water flow zone ((4)
in figure 1).
Methods of determining the temperature distribution of a mineral oil deposit
are known in
principle to those skilled in the art. It will generally be undertaken from
temperature
measurements at particular sites in the formation in combination with
simulation calculations,
the simulation calculations taking account of factors including amounts of
heat introduced into
the formation and the amounts of heat removed from the formation. By means of
biochemical
analyses, it is possible to detect the presence and amount of aerobic and
anaerobic
microorganisms in the region of the injection borehole (1) and of the
production borehole (2)
close to the base of the borehole. For this purpose, samples can be taken from
the formation. In
addition, the production water or injection water backwash can be analyzed for
the presence of
microorganisms.
Process step (la)
In the embodiment (la), at least one aqueous formulation of oil-mobilizing
microorganisms,
especially bacteria, is injected into the formation. The microorganisms may be
aerobic or
anaerobic, preferably anaerobic, microorganisms. In addition, a nutrient
solution and optionally
an oxygen source are injected into the mineral oil formation. The
microorganisms enter through
the injection boreholes at a site in the formation with the temperature (Ti).
Like the water
flooding in the preceding process step (0), the aqueous formulation flows
preferably into the
already partially exploited zone in the region between the injection borehole
and the production
borehole (i.e. zone (4) in figure 1), but it is not impossible that the
microorganism-containing
flooding medium additionally also flows via new flow paths.
PF 71956 CA 02823752 2013-07-03
The three components, microorganisms, nutrient solution and optionally an
oxygen source, can
be injected together, or else successively in individual portions, such that
microorganisms,
nutrient solution and optionally the oxygen source do not mix with one another
until within the
5 formation. The oxygen source may be an oxygen-forming substance, for
example hydrogen
peroxide, or preferably an oxygenous gas. An oxygenous gas can be injected as
such, or it is
possible with preference to inject an oxygenous flooding medium, especially
oxygenous water
or brine. The concentration of dissolved oxygen in the aqueous flooding
medium, especially
water, may, for example, be 0.05 to 0.5 m3 of oxygen / m3 of flooding medium.
An oxygenous
10 gas is injected in the case of use of aerobic microorganisms, and is
omitted in the case of use of
anaerobic microorganisms.
Suitable microorganisms for mobilizing mineral oil in a mineral oil formation
are known in
principle to the person skilled in the art, for example from the literature
cited at the outset.
Mineral oil can be mobilized on the basis of one or more of the following
mechanisms: formation
of surfactants, reduction in the viscosity of the mineral oil resulting from
degradation of high
molecular weight hydrocarbons, formation of CO2 and/or methane, formation of
organic acids
which can attack the rock formation and hence create new flow paths, or
resulting from the
detachment of the mineral oil from the rock surface.
Examples of suitable microorganisms are mentioned, for example, in "The
Phylogenetic
Diversity of Aerobic Organotrophic Bacteria from the Dagang High-Temperature
Oil Field"
T. N. Nazina, D. Sh. Sokolova, N. M. Shestakova, A. A. GI-I:goo/an, E. M.
Mikhallova, T. L.
Babich, A. M. Lysenko, T P. Tourova, A. B. Poltaraus, Qingxian Feng, Fangtian
Ni, and S. S.
Belyaev Microbiology, Vol. 74, No. 3, 2005, pp. 343-351. Translated from
Mikrobiologiya, Vol.
74, No. 3, 2005, pp. 401-409 or "Use of Microorganisms in the Biotechnology
for the Enhancement of Oil Recovery. S. S. Belyaev, I A. Borzenkov, T. N.
Nazina, E. P.
Rozanova, I F Glumov, R. R. lbatullin, and M. V. Ivanov, Microbiology, Vol.
73, No. 5, 2004,
pp. 590-598".
Examples of suitable microorganisms comprise anaerobic representatives of
various genera, for
example Clostridium sp., Bacillus sp., Desulfovibrio sp., Arthrobacter sp.,
Mycobacterium sp.,
Micrococcus sp., Brewbacillus sp., Actinomyces sp. or Pseudomonas sp..
Suitable nutrient solutions for microorganisms are known in principle to the
person skilled in the
art. They comprise, for example, phosphate or ammonium salts. They may
comprise, as main
components, for example, NaNO3, KNO3, NI-14NO3, Na2HPO4, NI-14C1, trace
elements, for
example B, Zn, Cu, Co, Mg, Mn, Fe, Mo, W, Ni, Se, vitamins such as folic acid,
ascorbic acid,
riboflavin, electron acceptors such as S042-, NO3-, Fe3+, humic acids, mineral
oxides, quinone
compounds or combinations thereof.
PF 71956 CA 02823752 2013-07-03
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The maximum growth rate of microorganisms depends on the temperature. The
temperature at
which the growth of the microorganisms is at its greatest shall be referred to
hereinafter as Tw.
In this context, the person skilled in the art distinguishes between different
classes of
microorganisms, namely psychrophilic, mesophilic, thermophilic and
hyperthermophilic bacteria,
and the temperature ranges of maximum growth rate may be defined slightly
differently
according to the literature reference. Table 3 below shows a typical
classification on which the
present invention shall be based.
Minimum Optimum Maximum
temperature temperature
Psychrophiles - 5 C 12 to 15 C 25 C
Mesophiles 15 C 30 to 40 C 47 C
Thermophiles 40 C 55 to 75 C 90 C
Hyperthermophiles 70 C 80 to 90 C 110 C
Table 2: Minimum, maximum and optimal growth temperature for different classes
of
microorganisms.
In order to achieve an optimal result, the type of microorganisms used should
be matched to the
temperature in the already partially exploited zone in the region between the
injection borehole
and the production borehole. According to the temperature of the zone
mentioned,
psychrophilic, mesophilic, thermophilic or hyperthermophilic microorganisms
are selected and,
within each class, also as far as possible those microorganisms which have a
maximum growth
rate at the temperature of the deposit in the partially exploited zone. In
general, Tw should be in
the range from Tito T.
PF 71956 CA 02823752 2013-07-03
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In table 3 below, some microorganisms are compiled, with the optimal growth
temperature for
each:
Psychrophiles Mesophiles Thermophiles Hyperthermophiles
Flavobacterium Escherichia coil Streptococcus Aquifex
pyrophilus
antarcticum 37 C thermophllus 85 C
15 C 45 C
Photobacterium Streptomyces Geobacillus Pyrodicthim brockii
pro fundum coelicolor stearothermophllus 85 - 105 C
C 28 C 55 C
She wanella benthica Bacillus subtilis Thermus aquaticus Pyrobaculum
4 C 30 C 70 C islandicum
95 - 100 C
Chlamydomonas nivalis Corynebacterium Streptomyces Methanopyrus
glutamicum the rmogriseus kandleri
30 C 55 - 60 C 98 C
Flavobacterium Pseudomonas Clostridium Ignisphaera
frigidarium putida stercorarium aggregans
C 26 C 60 C 92 C
Leptothrix mobllis Salmonella The rmovorax Archaeoglobus
C enter/ca subterraneus veneficus
- 37 C 70 C 75 C
Bacillus marinus Micrococcus Geothermobacter Geoglobus
20 C luteus ehrlkhil acetivorans
30 C 50 - 55 C 80 C
Table 3 : Optimal growth temperature of different microorganisms
5
It will be appreciated that it is also possible to use several different
microorganisms for process
step (la), for example microorganisms which evolve gases and microorganisms
which evolve
surfactants. The microorganisms can be injected together or else successively.
It is optionally
also possible to inject an aqueous formulation in each case, especially water,
between
10 individual formulations comprising microorganisms.
PF 71956 CA 02823752 2013-07-03
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The use of different microorganisms is advisable especially in the case of
mineral oil formations
with relatively large temperature differences Tp¨ T1, for example formations
with a temperature
difference Tp¨Ti of at least 20 C, especially of at least 30 C, for example
those with a
difference of 30 to 50 C. In a preferred embodiment of the invention,
therefore, n formulations
with different optimal growth temperatures Twn are injected, where n 2, and
where the optimal
growth temperature of each portion of the microorganisms injected decreases.
It is optionally
possible to inject flooding water in each case between individual formulations
comprising
microorganisms.
By means of the outlined preferred embodiment of the invention, microorganisms
can mobilize
additional mineral oil in the entire partially exploited region between the at
least one injection
borehole and the at least one production borehole, and not only in part of the
region thereof.
Figure 2 shows a schematic of the formation already shown, after the injection
of 3 different
portions of microorganisms (5).
Process step (lb)
In embodiment (lb), no microorganisms are injected into the formation, but
rather oil-mobilizing
microorganisms already present in the formation, especially bacteria, are
activated.
The microorganisms present are activated by injection of an aqueous nutrient
solution and
optionally of an oxygen source, especially of an oxygenous gas, and the gas
may also be
present in the nutrient solution. Details of the nutrient solutions and the
means of injecting
oxygen into the formation have already been outlined at the outset.
In one embodiment of process step (lb), it is possible to alternately activate
aerobic and
anaerobic microorganisms. In this case, oxygen-containing nutrient solution
and nutrient
solutions comprising only little oxygen, if any, are injected alternately.
The two process steps (la) and (lb) can of course be combined with one
another. For example,
in a first step, it is first possible to activate microorganisms present in
the formation and, in a
second step, to inject additional microorganisms, nutrient solution and
optionally oxygen into the
formation.
In process step (I), the production borehole(s) should not be sealed, but
rather the
abovementioned flooding media are injected continuously into the formation
and, accordingly,
mineral oil can also be withdrawn consistently through the production
borehole(s). This does not
rule out brief closure. In general, the production boreholes, however, should
be open over at
least 80% of the total time for process step (I).
PF 71956 CA 02823752 2013-07-03
14
By means of process step (I), mineral oil which has been immobilized to date
in the formation is
mobilized and, accordingly, the production of mineral oil can be enhanced
again, and the
watering out of production decreases.
Process step (II)
After the mobilization of mineral oil in the formation by means of process
step (I), the production
of mineral oil is continued by injection of flooding water into the injection
borehole and
withdrawal of mineral oil through the production borehole.
The oil mobilized by the microorganisms is thus produced by further water
flooding. As a result
of the continuing removal of oil from the already partially exploited zone,
the permeability of the
water flow zone increases further, and new, preferred flow paths ultimately
form again. This
again causes distinct watering out of production.
Process step (III)
In process step (III), highly permeable regions of the formation are blocked.
The highly
permeable regions are essentially the water flow zone which has already been
outlined, in the
region between the at least one injection borehole and the at least one
production borehole, i.e.
essentially that zone in which, in process step (I), the mobility of oil has
been improved by
injection or activation of microorganisms. However, it is also possible to
block further highly
permeable regions, for example those which have only formed as a result of
process step (II).
Techniques for blocking highly permeable regions of mineral oil formations are
known in
principle to those skilled in the art, for example from the literature cited
at the outset. These
involve injecting suitable aqueous formulations into the formation through the
injection borehole,
which can bring about closure of the highly permeable regions.
In a preferred embodiment of the invention, process step (III) is performed by
injecting at least
one aqueous, gel-forming formulation (F), said formulations (F) comprising
water and one or
more water-soluble or water-dispersible components which form high-viscosity
gels after
injection into the deposit under the influence of the deposit temperature.
After being injected into
the formation, the formulations (F) naturally flow esssentially through the
highly permeable
regions and close them after the gel has formed. This is shown schematically
in figure 3. A gel
plug (6) closes the highly permeable regions between the injection borehole
and the production
borehole.
Aqueous, gel-forming formulations for blockage of permeable regions of a
mineral oil formation
are known in principle to those skilled in the art. The aqueous, gel-forming
formulations (F)
comprise, as well as water, one or more different water-soluble or water-
dispersible chemical
components which are responsible for gel formation. These are preferably at
least two different
PF 71956 CA 02823752 2013-07-03
components. They may be either inorganic components or organic components, and
of course
also combinations of inorganic and organic components.
For example, they may be formulations based on water-soluble polymers, as
disclosed, for
5 example, by US 4,844,168, US 6,838,417 B2 or US 2008/0035344 Al, or
formulations based
essentially on inorganic components, as disclosed, for example, by SU 1 654
554 Al, US
4,889,563, RU 2 066 743 Cl, WO 2007/135617, US 7,273,101 B2 or RU 2 339 803
C2.
Suitable formulations are also commercially available.
10 The temperature from which gel formation sets in (referred to
hereinafter as Tgel) and the time
after which this occurs (referred to hereinafter as to) can be influenced, for
example, by the
type and concentration of the components. They can be adjusted such that gels
are formed
between 20 and 120 C, preferably 30 and 120 C and more preferably 40 and 120
C. The
citations cited comprise figures for this. The formulations can thus be
adjusted such that the
15 formulations form gels at the desired site in the highly permeable
regions and block the highly
permeable regions.
In a preferred embodiment, the formulation (F) is an acidic aqueous
formulation, preferably
having a pH 5, at least comprising
= water,
= a metal compound which is dissolved therein and can form gels when
admixed
with bases, and
= a water-soluble activator which brings about an increase in the pH of the
aqueous solution above a temperature T Tgel=
In addition to water, the formulation may optionally comprise further water-
miscible organic
solvents. Examples of such solvents comprise alcohols. In general, the
formulations (F) should,
however, comprise at least 80% by weight of water based on the sum of all
solvents in the
formulation, preferably at least 90% by weight and more preferably at least
95% by weight. Most
preferably, only water should be present.
The dissolved metal compound preferably comprises aluminum compounds,
especially
dissolved aluminum(III) salts, for example aluminum(III) chloride,
aluminum(III) nitrate,
aluminum(III) sulfate, aluminum(III) acetate or aluminum(III) acetylacetonate.
However, the
dissolved metal compound may also be already partially hydrolyzed
aluminum(III) salts, for
example aluminum hydroxychloride. It will be appreciated that it is also
possible to use mixtures
of several different aluminum compounds. The pH of the formulation is
generally 5, preferably
4.5. Preference is given to aluminum(III) chloride, aluminum(III) nitrate or
aluminum(III)
sulfate, very particularly preference to aluminum(III) chloride.
PF 71956 CA 02823752 2013-07-03
16
Useful water-soluble activators include all compounds which, when heated to a
temperature T>
Tgei in an aqueous medium, release bases or bind acids and hence ensure an
increase in the
pH of the solution. The increase in the pH forms high-viscosity, water-
insoluble gels which
comprise metal ions, hydroxide ions and optionally further components. In the
case of use of
aluminum compounds, an aluminum hydroxide or oxide hydrate gel may form, into
which further
components, for example the anions of the aluminum salt used, may of course
also comprise.
The water-soluble activators used may, for example, be urea, substituted ureas
such as N,N'-
alkylureas, especially N,N'-dinnethylurea, hexamethylenetetramine (urotropin)
or cyanates,
especially urea, substituted ureas or hexamethylenetetramine. Urea, for
example, is hydrolyzed
in an aqueous medium to ammonia and CO2. It will be appreciated that it is
also possible to use
mixtures of several different activators. Preference is given to urea and/or
hexamethylenetetramine.
The formulations may additionally comprise further components which can
accelerate or slow
gel formation. Examples comprise further salts or naphthenic acids.
The concentrations of the metal compounds used are selected by the person
skilled in the art
such that a gel forms with the desired viscosity. The activator will therefore
be used in such a
concentration that a sufficient amount of base can form to lower the pH to
such an extent that a
gel can actually precipitate out. In addition, the amounts and the ratios can
also be used to
determine the gel formation time tgel. The higher the concentration of the
activator - at a given
concentration of the metal compound - the higher the rate of gel formation.
This relationship can
be utilized by the person skilled in the art to deliberately accelerate or to
slow the gel formation
time Tgei. The rate of gel formation after exceedance of Tgei is naturally
also determined by the
temperature which exists in the formation. In the case of aluminum, an amount
of 0.2 to 3% by
weight of aluminum(III), based on the aqueous formulation, has been found to
be useful. The
amount of the activator should at least be such that 3 mol of base are
released per mol of
AI(III).
Table 4 below shows, by way of example, the time until gel formation for a
mixture of 8% by
weight of AlC13 (calculated as anhydrous product, corresponds to 1.6% by
weight of AI(III)), 25%
by weight of urea and 67% by weight of water.
Temperature [ C] 100 90 80 70 60
Gel formation time [days] 1/4 1 3 6 30
Table 4: Time until gel formation at different temperatures
Table 5 below shows the time until gel formation for different mixtures of
AlC13 (calculated as
anhydrous product), urea and water at 100 C or 100 C.
PF 71956 CA 02823752 2013-07-03
17
Amounts Weight ratio of AlC13 Time until gel formation
used / urea [h]
[% by wt.] 100 C 110 C
AlC13 4 1:4 4.0
urea 16
AlC13 4 1:3 4.3
urea 12
AlC13 4 1:2 7.3
urea 8
AlC13 4 1:1 19.0
urea 4
AlC13 8 1:3.75 5.3 2
urea 30
AlC13 2 1:3.75 8
urea 7.5
AlC13 8 1:3 5.5
urea 24
AlC13 8 1:2 8.3
urea 16
AlC13 8 1:1 18.0
urea 8
AlC13 8 1:0.75 23.0
urea 6
Table 5: Time until gel formation ("-" no measurement)
It can be seen that, with decreasing amount of the urea activator, the time to
formation of the
gel becomes ever longer both for the series with 8% by weight of AlC13 and the
series with 4%
by weight of AlC13 with decreasing amount of urea. The gel formation time can
thus be altered
in a controlled manner via the aluminum salt / urea ratio.
Gel-forming formulations which are particularly suitable for low deposit
temperatures can be
obtained by replacing all or some of the urea as an activator with urotropin
(hexamethylenetetramine) as an activator. Urotropin likewise releases ammonia
under deposit
conditions. Such gel-forming formulations also lead to gel formation at
temperatures below
50 C. Typical aqueous formulations may comprise 4 to 16% by weight of urea, 2
to 8% by
weight of urotropin and 2 to 4% by weight of aluminum chloride or nitrate
(calculated as
anhydrous salt) and water or salt water. Such formulations are disclosed, for
example, by RU 2
066 743 Cl. Table 6 below compares some formulations disclosed in RU 2 066 743
Cl, pages
5 to 7, and the gel formation thereof at different temperatures.
-13
=
11
V
8
01
CD
No. Components "Yo by wt.
Viscosity ri Temperature
before heat 20 C 50 C
70 C 90 C
treatment Gel formation 9 tGel n
tGel rl tGel 11
[MPa.s] time [MPa.s] [days] [MPa.s]
[days] [MPa.s] [days] [MPa.s]
tGel [days]
1 Urea 16.0 No gel No gel
AlC13 4.0 2.4 100 formation 27
formation 4 3240
2 Urea 16.0
AlC13 4.0
Urotropin 8.0 2.4 3 6960 1 4980
0.5 2500.0 0.5 2700
4 Urea 16.0
AlC13 4.0
Urotropin 6.0 1.5 2 1830 3 4100
1 2100.0 1 2800.0 n
8 Urea 16
0
iv
AlC13 2.0
co
Urotropin 8.0 2.0 7 374.0 3 3870
1 2100.0 0.5 1200.0
-.3
9 Urea 16
K)
AlC13 4.0
iv
0
H
Urotropin 4.0 1.5 7 1300.0 2 3500
u.)
1
Urea 8.0
0
-.3
1
AlC13 4.0
0
u.)
Urotropin 8.0 1.6 2 3210 2 6100
1 2870.0 0.5 2900.0
7 Urea 8.0
AlC13 2.0
Urotropin 4.0 1.6 4 600.0 4 6050
1 2200.0 1 2300.0
6 Urea 6.0
AlC13 4.0
Urotropin 8.0 1.5 2 1830 2 4100
1 2500.0 1 5800.0
3 Urea 4.0
AlC13 4.0
Urotropin 8.0 1.4 7 2960 2 3790
1 2310.0 1 2300.0
Table 6: Gel formantion as a function of temperature and time
PF 71956 CA 02823752 2013-07-03
19
The described preferred formulations based on dissolved metal compounds,
especially
aluminum salts, and activators have the advantage that inorganic gels are
formed. In addition,
the inorganic gels can also be removed very easily from the formation again if
required, by
injecting acid into the formation and dissolving the gels.
Further examples of gel-forming aqueous formulations comprise formulations
based on
polyacrylamides and trivalent or tetravalent cations, for example Cr(III),
Fe(III) or Zr(IV) as
crosslinkers. In the case of use of this system, acrylamide groups are
hydrolyzed at least partly
to carboxylate groups, which can crosslink with the cations. On application,
polyacrylamides
with different degrees of hydrolysis can used, which can achieve different
gelation times and
penetration depths.
As a further alternative, it is possible to use silicate gels, for example
colloidal silicate gels or
combined polymer/silicate gels. Sodium silicate forms, with different
chemicals, a sol or a gel-
like material which can reduce permeability. The gel can be varied within wide
ranges in relation
to density, viscosity, solids contents and other properties. The advantages of
the system are low
operating costs and stability at relatively high temperatures. It is also
known that silicate
solutions can be used in combination with polymers, for example
polyacrylamide. This allows
improved long-term stability (aging) and better thermal stability to be
achieved.
Process step (IV)
After the closure of the highly permeable regions of the mineral oil formation
in the region
between the injection and production boreholes, the production of mineral oil
is continued by
injection of flooding water and withdrawal of mineral oil through the at least
one production
borehole.
Since the existing flooding paths have been closed with a gel in the course of
process step (III)
and flow through them is accordingly no longer possible, mineral oil from low-
permeability
regions of the mineral oil formation which have not been covered by the water
flooding to date is
also collected, and it is thus possible to produce further mineral oil from
the formation. This is
shown schematically in figure 4. The original flooding path (4) has been
closed by means of a
gel plug, and a new flooding path (7) is formed, through which mineral oil is
forced out of the
formation to the production borehole. Details of the displacement of the
mineral oil and, where
appropriate, the formation of preferred flooding paths have already been
specified in the
description of process step (I).
Process step (V)
To further enhance the mineral oil yield, after performance of process step
(IV), process step
(V) is conducted. Unless stated otherwise, this is a repetition of process
step (I).
PF 71956 CA 02823752 2013-07-03
Process step (V) should be carried out no later than recurrence of watering
out of production
which is no longer acceptable in process step (IV). However, it can also be
carried out at an
earlier stage, for example when the formation in the region of the new
flooding path has a very
5 low permeability, such that mineral oil production is unsatisfactory.
According to the duration of
water flooding in process step (IV), the temperature in the region of the new
flooding paths may
be lowered only slightly or lowered significantly compared to the formation
temperature. In
addition, the temperature difference between the injection borehole and
production borehole Tp
¨ Ti may be very different. In the case of only a short duration of the water
flooding, it may be
10 very low, for example only Ito 5 C, and in the case of long duration it
may be very marked as
already outlined above, for example 5 C to 60 C, preferably 10 C to 55 C and
more preferably
15 C to 50 C.
For process step (V) too, two variants should be distinguished, namely the
injection of
15 microorganisms into the formation (process step (Va)) or the activation
of oil-mobilizing
microorganisms already present in the formation (process step (Vb)). By means
of the injection
or the activation of microorganisms, additional mineral oil in the new flood
zone can be
mobilized. This is shown schematically in figure 5.
20 In preferred embodiments of the invention, the microorganisms injected
in process step (la) and
process step (Va) are particularly matched to one another.
In one embodiment, mesophilic microorganisms are injected in process step
(la), and
thermophilic and/or hyperthermophilic microorganisms in process step (V).
In a further embodiment, psychrophilic microorganisms are injected in process
step (la), and
mesophilic and/or thermophilic and/or hyperthermophilic microorganisms in
process step (V).
Both variants are particularly suitable for formations in which the flow zone
in process step (I)
has already cooled distinctly, and already has a temperature distinctly below
the deposit
temperature TL. In this case, it is advantageous to mobilize mineral oil using
microorganisms
which can already grow at comparatively low temperatures. The flow zone which
newly forms in
process step (IV) is within less permeable regions of the formation and can
accordingly cool to a
lesser degree. It is therefore advisable here to use microorganisms which have
a higher optimal
growth temperature than those used in step (I).
Process step (VI)
After the mobilization of mineral oil in the formation by means of process
step (IV), the
production of mineral oil is continued by injecting flooding water into the
injection borehole and
withdrawing mineral oil through the production borehole. The oil mobilized by
the
microorganisms is thus produced by further water flooding.
= PF 71956 CA 02823752 2013-07-03
21
Further process variants
The process according to the invention may also comprise further variants.
It is possible, for example, to repeat process steps (III), (IV), (V) and (VI)
for a second time. In
this case, the new flood zone formed in the course of the process is closed by
means of a gel,
and a further flood zone is formed between the injection borehole and the
production borehole.
The process according to the invention can also be used when mineral oil is to
be produced
simultaneously from a group of horizons (strata at different depth) with
different permeability.
This is shown schematically in figure 6. Figure 6 shows, schematically, an
injection borehole (1)
and a production borehole (2) which are set up for oil production from two
different horizons. In
this embodiment, process step (I) is first applied to the already cooled
horizon with high
permeability (9) (figure 6a). Finally, the horizon (9) is closed by applying a
gel-forming
formulation (process step OW. The closure is followed by production from the
second horizon
(10) which has the original deposit temperature, and microorganisms are
employed to mobilize
mineral oil. In the cooled horizon (9), portions (5) of microorganisms
(psychrophilic or
mesophilic) are injected. In the horizon (10) with elevated temperature,
portions (8) of
microorganisms (thermophilic or hyperthermophilic) are injected.
The process according to the invention comprising a combination of the use of
microbiological
methods (Microbiological Enhanced Oil Recovery (MEOR)) to increase the oil
yield and the
blockage of highly permeable regions of the mineral oil formation (conformance
control) leads to
an improvement in oil yield and hence in exploitation of the formation.
Compared to other
methods/processes for improving the oil yield, the MEOR method is inexpensive.
The
combination with conformance control is thus also a very economically viable
process.
