U.S. patent application number 13/631653 was filed with the patent office on 2013-04-04 for process for producing mineral oil from an underground deposit.
This patent application is currently assigned to Wintershall Holding GmbH. The applicant listed for this patent is Bernd Leonhardt, VLADIMIR STEHLE, Benjamin Wenzke. Invention is credited to Bernd Leonhardt, VLADIMIR STEHLE, Benjamin Wenzke.
Application Number | 20130081809 13/631653 |
Document ID | / |
Family ID | 47991534 |
Filed Date | 2013-04-04 |
United States Patent
Application |
20130081809 |
Kind Code |
A1 |
STEHLE; VLADIMIR ; et
al. |
April 4, 2013 |
PROCESS FOR PRODUCING MINERAL OIL FROM AN UNDERGROUND DEPOSIT
Abstract
A process for producing mineral oil, in which an aqueous
flooding medium comprising water, a glucan, urea and optionally
surfactants is injected into the mineral oil formation and mineral
oil is withdrawn from the formation through at least one production
well, wherein the formation has a temperature of at least
60.degree. C. The formulation forms in situ foams in the formation
under the influence of the formation temperature.
Inventors: |
STEHLE; VLADIMIR; (Kassel,
DE) ; Leonhardt; Bernd; (Kassel, DE) ; Wenzke;
Benjamin; (Hamburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STEHLE; VLADIMIR
Leonhardt; Bernd
Wenzke; Benjamin |
Kassel
Kassel
Hamburg |
|
DE
DE
DE |
|
|
Assignee: |
Wintershall Holding GmbH
Kassel
DE
|
Family ID: |
47991534 |
Appl. No.: |
13/631653 |
Filed: |
September 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61542840 |
Oct 4, 2011 |
|
|
|
Current U.S.
Class: |
166/272.6 |
Current CPC
Class: |
C09K 8/588 20130101 |
Class at
Publication: |
166/272.6 |
International
Class: |
E21B 43/24 20060101
E21B043/24 |
Claims
1. A process for producing mineral oil from an underground mineral
oil deposit into which at least one production well and at least
one injection well have been sunk, each of which is connected to
the deposit, said process comprising at least one process step (B)
in which mineral oil is produced by injection of an aqueous
flooding medium comprising water-soluble thickening polymers
through the injection well and withdrawing mineral oil through the
production well, wherein the temperature during process step (B) at
least in a partial region of the mineral oil formation between the
injection and production wells is at least 60.degree. C. and the
aqueous flooding medium comprises, as well as water, at least a
glucan (G) with a .beta.-1,3-glycosidically linked main chain and
side groups .beta.-1,6-glycosidically bonded thereto, said glucan
having a weight-average molecular weight M.sub.w of 1.5*10.sup.6 to
25*10.sup.6 g/mol, and urea.
2. The process according to claim 1, wherein the aqueous flooding
medium used in process step (B) comprises 15 to 300 g/l of urea and
0.1 to 5 g/l of the glucan (G).
3. The process according to claim 2, wherein the aqueous flooding
medium used in process step (B) additionally comprises 50 to 250
g/l of an ammonium salt.
4. The process according to claim 2, wherein the aqueous flooding
medium used in process step (B) additionally comprises 0.1 to 5 g/l
of a surfactant.
5. The process according to claim 1, wherein the temperature at
least in a partial region of the mineral oil formation between the
injection and production wells is at least 80.degree. C.
6. The process according to claim 1, wherein the temperature at
least in a partial region of the mineral oil formation between the
injection and production wells is 80.degree. C. to 120.degree.
C.
7. The process according to claim 1, wherein the process comprises
an additional process step (A) which is performed before process
step (B), and in which either an aqueous flooding medium (process
step (A1)) or steam (process step (A2)) is injected.
8. The process according to claim 1, wherein the process comprises
an additional process step (C) which is performed after process
step (B), and in which either an aqueous flooding medium (process
step (C1)) or steam (process step (C2)) is injected.
9. The process according to claim 7, which involves process step
(Al) wherein the aqueous flooding medium injected comprises, as
well as water, at least one glucan (G), with the proviso that the
amount of this glucan (G) is such that the viscosity of the aqueous
flooding medium injected in process step (A1) is less than the
viscosity of the aqueous flooding medium injected in process step
(B).
10. The process according to claim 8, which involves process step
(C1) wherein the aqueous flooding medium injected comprises, as
well as water, at least one glucan (G), with the proviso that the
amount of this glucan (G) is such that the viscosity of the aqueous
flooding medium injected in process step (C1) is greater than the
viscosity of the aqueous flooding medium injected in process step
(B).
11. The process according to claim 7, wherein the aqueous flooding
media injected in process steps (A1) and/or (C1) have a temperature
of at least 80.degree. C.
12. The process according to claim 7, wherein either steam or an
aqueuos flooding medium with a temperature of at least 80.degree.
C. is injected in process step (A), and wherein an aqueous flooding
medium with a temperature of less than 40.degree. C. is
additionally injected between process steps (A) and (B).
13. The process according to claim 8, wherein either steam or an
aqueuos flooding medium with a temperature of at least 80.degree.
C. is injected in process step (C), and wherein an aqueous flooding
medium with a temperature of less than 40.degree. C. is
additionally injected between process steps (B) and (C).
14. The process according to claim 12, wherein the aqueous flooding
media injected between (A) and (B) and/or (B) and (C) comprise at
least one glucan (G).
15. The process according to claim 14, which comprises at least one
additional process step (D) for blocking of highly permeable
regions of the underground mineral oil formation, and in which an
aqueous flooding medium which is injected comprises, as well as
water, at least a glucan (G) with a .beta.-1,3-glycosidically
linked main chain and side groups .beta.-1,6-glycosidically bonded
thereto, said glucan having a weight-average molecular weight
M.sub.w of 1.5*10.sup.6 to 25*10.sup.6 g/mol, urea, and at least
one water-soluble aluminum(III) salt and/or a partly hydrolyzed
aluminum(III) salt.
16. The process according to claim 15, wherein process step (D) is
performed after process step (B) and then the process is continued
with another performance of process step (B).
Description
[0001] The present invention relates to a process for producing
mineral oil, in which an aqueous flooding medium comprising water,
a glucan, urea and optionally surfactants is injected into the
mineral oil formation and mineral oil is withdrawn from the
formation through at least one production well, wherein the
formation has a temperature of at least 60.degree. C. The
formulation forms in situ foams in the formation under the
influence of the formation temperature, and also gases which lead
to formation of an alkaline bank in the oil-bearing stratum.
[0002] 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 the natural gas dissolved therein in a
natural manner, 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 .mu.m; the formation may additionally also have
regions with pores of greater diameter and/or natural fractures or
fissures.
[0003] After the well has been sunk into the oil-bearing strata,
the oil at first flows to the production wells 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.
[0004] In order to enhance the yield, what are known as secondary
production processes are therefore used.
[0005] The most commonly used process in secondary mineral oil
production is water flooding. This involves injecting water through
the injection wells into the oil-bearing strata. This artificially
increases the deposit pressure and forces the oil out of the
injection wells to the production wells. Water flooding in the case
of production of relatively high-viscosity mineral oils can enhance
the yield level only slightly.
[0006] In the ideal case of water flooding, a water front
proceeding from the injection well should force the oil
homogeneously over the entire mineral oil formation to the
production well. 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
fissures or very permeable regions in the reservoir rock. Such
permeable regions may also be regions from which oil has already
been substantially recovered by the water. In the course of water
flooding, the flooding water injected naturally flows principally
through flow paths with low flow resistance from the injection well
to the production well. The consequences of this are that the
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 wells. 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 relatively high-viscosity mineral oils. The higher the
mineral oil viscosity, the more probable is rapid watering out of
production.
[0007] In order to counteract the above-described adverse effects
in the production of mineral oils, especially viscous mineral oils,
various measures are known in the prior art.
[0008] For example, the preferred flow paths for injected flooding
water can be blocked. For this purpose, it is possible to use
gel-forming formulations which are of comparatively low viscosity
before injection and form highly viscous gels in the formation
after injection. This blocks preferred flow paths for the flooding
water and diverts the water into regions from which oil has yet to
be recovered. Such measures are also known as "Conformance Control"
or `Water shut-off`. Altunina, L. K., Kuvshinov, V. A. "Improved
Oil Recovery of High-Viscosity Oil Pools with Physicochemical
Methods and Thermal-Steam Treatments", Oil & Gas Science and
Technology, Vol. 63 (2008), No. 1, pages 37 to 48 disclose the use
of cellulose ethers for mineral oil production. Aqueous solutions
of cellulose ethers are of relatively low viscosity at room
temperature and do not form highly viscous gels until relatively
high temperatures. It is possible to add urea or ammonium
thiocyanate to the cellulose ether formulations in order to
influence the gel formation temperature.
[0009] It is additionally known that suitable measures can be taken
to match the viscosities of the water and oil phases to one
another. For this purpose, the oil viscosity can be reduced and/or
the viscosity of the aqueous flooding medium can be increased.
Measures for reduction of the oil viscosity are, for example,
CO.sub.2 flooding and steam flooding. CO.sub.2 flooding reduces the
oil viscosity by the action of the CO.sub.2, and steam flooding by
the increase in the temperature. The viscosity of the aqueous
flooding media can be enhanced by the addition of suitable
viscosity-enhancing additives. Examples thereof include polymer
flooding, in which the viscosity of the aqueous phase is increased
by the addition of polymers, or foam flooding.
[0010] For polymer flooding, a multitude of different thickening
water-soluble polymers have been proposed, both synthetic polymers,
for example polyacrylamide or copolymers of acrylamide and other
monomers, more particularly monomers having sulfo groups, and
polymers of natural origin, for example glucosylglucans, xanthans
or diutans. Glucosylglucans are branched homopolysaccharides formed
from glucose units. The preparation of such glucosylglucans and the
use thereof for mineral oil production is disclosed, for example,
in EP 271 907 A2, EP 504 673 A1, DE 40 12 238 A1 and WO 03/016545.
Glucosylglucans have a high thermal stability and are therefore
especially suitable for mineral oil deposits with high deposit
temperatures. Our prior application EP 11154670.1 discloses a
process for producing mineral oil from deposits with a deposit
temperature of at least 70.degree. C. using glucans.
[0011] Altunina, L.K., Kuvshinov, V.A. and Stasyeva, L. A.
"Thermoreversible Polymer Gels for EOR", in Recent Innovations in
Oil and Gas Recovery, Istvan Lakatos (Ed.)--Akademiai Kiado,
Budapest, Progress in Oilfield Chemistry, Vol. 8, pages 133 to 144,
2009 disclose the use of methylcellulose gels for tertiary mineral
oil production. The gels may comprise additives to increase the gel
formation temperature, for example ethanol, ammonium thiocyanate,
thiourea or urea.
[0012] Various techniques for foam flooding are disclosed, for
example, in the publications cited below:
[0013] U.S. Pat. No. 5,074,358 and U.S. Pat. No. 5,363,915 disclose
processes for tertiary mineral oil production, in which foams are
used. The gases used for foaming may, for example, be CO.sub.2,
N.sub.2 or CH.sub.4. The foam can be formed either by alternately
injecting gas and foam-forming formulations into the formation or
by forming a foam and injecting the foam into the formation (see,
for example, U.S. Pat. No. 5,363,915, column 6, lines 3 ff.).
[0014] Drozdov A. N., Telkov V. P., Egorov Yu. A. et al. disclose,
in "Solution of problems of water-gas influence (WGI) on the layer
using jet and electrical centrifugal pumping technology"--Society
of Petroleum Engineers SPE Paper 117380, the injection of a mixture
of water, natural gas and surfactant into a mineral oil deposit to
increase the yield.
[0015] Hombrook M. W., Dehgham K., Qadur S. Ostermann K. D., Ogbe
D. Q. "Effects of CO.sub.2 addition to steam on recovery of west
sak crude oil" SPE, Reservoir Eng.--1991--6 N.sup.o 3, p. 278-286
disclose a process in which a mixture of steam and CO.sub.2 is
injected into a mineral oil deposit.
[0016] U.S. Pat. No. 5,307,878 likewise discloses a process for
tertiary mineral oil production, in which foams are used. To
stabilize the foam, an essentially uncrosslinked polymer is
additionally used. The polymers mentioned are a multitude of
different polymers, for example synthetic polymers such as
polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone,
polyacrylamide, partly hydrolyzed polyacrylamide or natural
polymers such as xanthan, scleroglucan, hydroxypropylcellulose or
hydroxyethylcellulose.
[0017] RU 2 190 091 C2 discloses a multistage process for tertiary
mineral oil production, in which a polymer solution is first
injected, then a foam-forming formulation and a gas, and then a
polymer solution again. The aqueous foam-forming formulation
comprises water, alkali, a surfactant and a water-soluble polymer
with M.sub.n 300 to 30,000 g/mol. The polymer may, for example, be
xanthan, guar gum, polyacrylamide or partly hydrolyzed
polyacrylamide.
[0018] In the case of separate injection of foam-forming
formulations and gases to form foams in the deposit, the gases have
to mix with the foam-forming formulation underground after
injection into the deposit, in order to form a foam. However,
homogeneous and complete mixing underground is generally impossible
to achieve. Instead, a considerable portion of the foam-forming
formulations does not come into contact with the gases, such that
the homogeneous foam bank is not formed in the formation. The gases
escape predominantly into the higher regions of the deposit, and
the liquid into the lower regions. The mixing of the gases with
liquid in storage zones relatively far from the injector (20-100 m)
is therefore barely possible in the case of serial pumping of
foam-forming formulations and gases. The technique of forming the
foam at the surface is complicated, requires additional equipment
and also does not guarantee that the foam reaches regions of the
deposit relatively far-removed from the injector.
[0019] There are therefore known techniques for forming gases in
situ in the deposit by means of suitable measures to form foams,
rather than injecting them.
[0020] RU 2 361 074 C2 discloses a process in which an aqueous
solution of urea, ammonium nitrate, ammonium thiocyanate and
surfactants, and also--alternately therewith--steam are injected
into a mineral oil deposit. In the deposit, the urea is hydrolyzed
to form CO.sub.2 and ammonia in the deposit, which bring about an
enhancement of oil recovery.
[0021] Bocksermann A., Kotscheschkov A., Tarasov A. disclose, in
"Vervollkommnung der thermischen Methoden zur Entolungssteigerung
der Erdollagerstatten"[Enhancement of the thermal methods for
increasing oil recovery from mineral oil deposits], Russian
Institute for Scientific and Technical Information, "Development of
oil and gas deposits" series, volume 24, Moscow 1993, a process for
oil production in which water flooding or steam flooding is
combined with cyclic pumping of aqueous urea solutions. Under the
action of the deposit temperature or the steam temperature, the
urea is hydrolyzed to CO.sub.2 and ammonia. The gases released
promote the oil recovery from the mineral oil deposit.
[0022] However, foam formation is frequently also inadequate in the
case of the methods mentioned. The mixture of water and urea
injected can mix with deposit water present in the deposit after
injection and is diluted as a result. This complicates foam
formation and completely prevents it in the case of excessive
dilution.
[0023] It was an object of the invention to provide an improved
process for producing oil by means of foam flooding.
[0024] Accordingly, a process has been for producing mineral oil
from an underground mineral oil deposit into which at least one
production well and at least one injection well have been sunk,
each of which is connected to the deposit, said process comprising
at least one process step (B) in which mineral oil is produced by
injection of an aqueous flooding medium comprising water-soluble
thickening polymers through the injection well and withdrawing
mineral oil through the production well, wherein the temperature
during process step (B) at least in a partial region of the mineral
oil formation between the injection and production wells is at
least 60.degree. C. and wherein the aqueous flooding medium
comprises, as well as water, at least [0025] a glucan (G) with a
.beta.-1,3-glycosidically linked main chain and side groups
.beta.-1,6-glycosidically bonded thereto, said glucan having a
weight-average molecular weight M.sub.w of 1.5*10.sup.6 to
25*10.sup.6 g/mol, and [0026] urea.
INDEX OF FIGURES
[0027] FIG. 1 Dependence of the viscosity of the glucan (G) No. P1
and of comparative polymers V1 and V2 on concentration
[0028] FIG. 2 Temperature dependence of the viscosity of the glucan
(G) No. P1 and of the comparative polymers V1, V2 and V3 in
ultrapure water
[0029] FIG. 3 Temperature dependence of the viscosity of the glucan
(G) No. P1 and of the comparative polymers P1, V1, V2 and V3 in
deposit water
[0030] FIG. 4 Schematic diagram of mineral oil production by means
of the process according to the invention
[0031] FIG. 5 Schematic diagram of mineral oil production by means
of the process according to the invention after the performance of
conformance control measures
[0032] FIG. 6 Formation of CO.sub.2 by decomposition of urea in a
glucan (G) solution at 90.degree. C.
[0033] The following specific details of the invention are
given:
PROCESS PRINCIPLE
[0034] To execute the process according to the invention, at least
one production well and at least one injection well are sunk into
the mineral oil deposit. In general, a deposit is provided with
several injection wells and with several production wells.
[0035] Through the injection wells, flooding media, for example
aqueous flooding media or steam, can be injected into the deposit.
As a result of the pressure generated by the flooding media
injected, the mineral oil flows in the direction of the production
well and is produced through the production well. The term "mineral
oil" in this context does not of course mean only single-phase oil;
instead, the term also comprises the typical crude oil-deposit
water emulsions.
[0036] The mineral oil may in principle be any kind of mineral oil.
However, the deposits may preferably be those comprising viscous
mineral oil. The mineral oil present in the deposit may, for
example, have a viscosity .eta..sub.oil of at least 30 mPa*s,
(measured at the natural deposit temperature).
[0037] In addition to the oil, the mineral oil formation may
comprise deposit water with a greater or lesser salt content. The
salts in the deposit water may especially be alkali metal salts and
alkaline earth metal salts. Examples of typical cations comprise
Na.sup.+, K.sup.+, Mg.sup.2+ or Ca.sup.2+, and examples of typical
anions comprise chloride, bromide, hydrogencarbonate, sulfate or
borate. The salt content of the deposit water may be 20,000 ppm to
350,000 ppm (parts by weight based on the sum of all components of
the deposit water), for example 100,000 ppm to 250,000 ppm. The
amount of alkaline earth metal ions, especially of Mg.sup.2+ and
Ca.sup.2+ ions, may be 1000 to 53 000 ppm.
[0038] In general, deposit water comprises one or more alkali metal
ions, especially Na.sup.+ ions. In addition, alkaline earth metal
ions may also be present, in which case the weight ratio of alkali
metal ions/alkaline earth metal ions is generally .gtoreq.2,
preferably .gtoreq.3. The anions present are generally at least one
or more than one halide ion, especially at least chloride ions. In
general, the amount of Cl.sup.- is at least 50% by weight,
preferably at least 80% by weight, based on the sum of all
anions.
[0039] The process according to the invention comprises at least
one process step (B), in which an aqueous flooding medium
comprising at least water, a glucan (G) with a
.beta.-1,3-glycosidically linked main chain and side groups
.beta.-1,6-glycosidically bonded thereto, and urea is used. After
injection into the deposit, the urea decomposes under the influence
of the deposit temperature to form CO.sub.2 and NH.sub.3.
[0040] The process may optionally comprise at least one additional
process step (A) which is executed before a process step (B), and
in which flooding media are likewise injected into the deposit. The
flooding medium is preferably either an aqueous flooding medium
(process step (A1)) or steam (process step (A2)).
[0041] The process may optionally comprise at least one additional
process step (C) which is executed after a process step (B), and in
which flooding media are likewise injected into the deposit. The
flooding medium is preferably either an aqueous flooding medium
(process step (C1)) or steam (process step (C2)).
[0042] It will be appreciated that process step (B) and the
optional process steps (A) and (C) can be executed more than once.
They can, for example, be executed repeatedly in a cycle.
[0043] The process may also optionally comprise further process
steps. This may involve a further process step (D). In step (D), a
formulation of a thermogel thickened by means of a glucan (G) is
injected, i.e. a formulation which, after injection, can form
highly viscous gels under the influence of the formation
temperature. This can block permeable regions of the formation,
such that subsequently injected aqueous flooding media have to flow
via new flow paths. This can mobilize further oil.
[0044] According to the invention, the temperature during process
step (B), at least in a partial region of the mineral oil formation
between the injection and production wells, is at least 60.degree.
C., preferably at least 70.degree. C., more preferably at least
80.degree. C. and, for example, at least 90.degree. C. It should
not exceed 150.degree. C., preferably 135.degree. C. and more
preferably 120.degree. C. It may be 60.degree. C. to 150.degree.
C., especially 70.degree. C. to 140.degree. C., preferably
75.degree. C. to 135.degree. C. and more preferably 80.degree. C.
to 120.degree. C.
[0045] The term "region between the injection and production wells"
here means that part of the underground formation which is covered
by the flooding operation in the course of process step (B), i.e.
those regions through which the injected flooding media and/or the
mineral oil mobilized as a result flow from the injection well to
the production well during the flooding operation. Naturally, this
is not the shortest path from the injection well to the production
well. Instead, the flow paths are guided by the geological
conditions in the formation, and they may therefore also be longer.
According to the invention, the temperature at least in a partial
region thereof may have the above values. Preferably, the
temperature in the entire region of the injection and production
wells may have the values mentioned. The temperature in the entire
region between the injection and production wells should not exceed
the abovementioned maximum temperatures of 150.degree. C.,
preferably 135.degree. C. and more preferably 120.degree. C.
[0046] The temperatures mentioned may be the natural deposit
temperature. The natural deposit temperature can, however, be
altered by flooding operations preceding process step (B). If the
deposit is flooded, for example, with cold water for a prolonged
period before performance of process step (B), the temperature of
the deposit is lowered proceeding from the injection well, in which
case the temperature approaches the natural deposit temperature
again with increasing distance from the injection well. If the
deposit, in contrast, is flooded with hot steam for a prolonged
period before the performance of process step (B), the temperature
of the deposit is increased proceeding from the injection well.
[0047] The temperature distribution in the formation can optionally
be determined before the performance of process step (B). Methods
for determination of the temperature distribution in a mineral oil
deposit are known in principle to those skilled in the art. The
temperature distribution is generally undertaken from temperature
measurements at particular sites in the formation in combination
with simulation calculations, the latter taking into account
factors including amounts of heat introduced into the formation and
the amounts of heat removed from the formation.
[0048] Process According to the Invention
[0049] Glucans Used
[0050] "Glucans" are understood by the person skilled in the art to
mean homopolysaccharides formed exclusively from glucose units.
According to the invention, a specific class of glucan is used,
specifically those glucans which comprise a main chain formed from
.beta.-1,3-glycosidically linked glucose units, and side groups
which are formed from glucose units and are
.beta.-1,6-glycosidically linked thereto. The side groups
preferably consist of a single .beta.-1,6-glycosidically attached
glucose unit, with--viewed statistically--every third unit of the
main chain .beta.-1,6-glycosidically linked to a further glucose
unit.
[0051] Such glucans are secreted by specific fungal strains, and
corresponding fungal strains are known to those skilled in the art.
Examples comprise Schizophyllum commune, Sclerotium rolfsii,
Sclerotium glucanicum, Monilinia fructigena, Lentinula edodes or
Botrytis cinera. Suitable fungal strains are specified, for
example, in EP 271 907 A2 and EP 504 673 A1, claim 1 of each. The
fungal strains used are preferably Schizophyllum commune or
Sclerotium rolfsii and more preferably Schizophyllum commune, which
secretes a glucan in which, on a main chain formed from
.beta.-1,3-glycosidically linked glucose units--viewed
statistically--every third unit of the main chain is
.beta.-1,6-glycosidically linked to a further glucose unit; in
other words, the glucan is preferably what is called schizophyllan.
The glucans used for the invention have a weight-average molecular
weight Mw of approx. 1.5 to approx. 25*10.sup.6 g/mol, especially 2
to approx. 15*10.sup.6 g/mol.
[0052] The production of such glucans is known in principle. For
production, the fungi are fermented in a suitable aqueous nutrient
medium. In the course of fermentation, the fungi secrete the
abovementioned class of glucans into the aqueous fermentation
broth, and an aqueous polymer solution can be removed from the
aqueous fermentation broth. Processes for fermenting such fungal
strains are known in principle to those skilled in the art, for
example from EP 271 907 A2, EP 504 673 A1, DE 40 12 238 A1, WO
03/016545 A2 and Udo Rau, Viosynthese, Produktion and Eigenschaften
von extrazellularen Pilz-Glucanen" [Biosynthesis, Production and
Properties of Extracellular Fungal Glucans], Habilitation Thesis,
Technische Universitat Braunschweig, Shaker Verlag Aachen 1997",
each of which also mentions suitable nutrient media. The
fermentation systems may be continuous or batchwise systems.
[0053] An aqueous solution comprising glucans is ultimately removed
from the fermentation broth which comprises dissolved glucans and
biomass (fungal cells, with or without cell constituents), leaving
an aqueous fermentation broth in which the biomass has a higher
concentration than before. The removal can especially be effected
by means of single-stage or multistage filtration, or by means of
centrifugation. It will be appreciated that it is also possible to
combine several removal steps with one another.
[0054] In the removal, it should be ensured that the biomass is
very substantially retained. Biomass remaining in the filtrate can
block fine pores of the mineral oil formation. The quality of the
filtrate can be determined in a manner known in principle by means
of the millipore filtration ratio (MPFR). The test method is
outlined in EP 271 907 B1, page 11, lines 24 to 48. The MPFR of the
filtrates should be at a minimum, and especially 1.001 to 3,
preferably 1.01 to 2.0.
[0055] The filtration can preferably be undertaken by means of
crossflow filtration, especially crossflow microfiltration. The
crossflow microfiltration process is known in principle to the
person skilled in the art and is described, for example, in "Melin,
Rautenbach, Membranverfahren [Membrane processes], Springer-Verlag,
3rd edition, 2007, page 309 to page 366'. "Microfiltration" is
understood by the person skilled in the art here to mean the
removal of particles of a size between approx. 0.1 .mu.m and
approx. 10 .mu.m. A process for producing glucans using crossflow
filtration is disclosed in WO 2011/082973 A2.
[0056] The glucans can be removed from the filtrate obtained.
Preferably, however, the glucans are not removed, and the resulting
aqueous glucan solution is instead used directly for production of
the flooding media for process step (B). The concentration of the
glucan solutions obtained may, for example, be 5 to 25 g/l.
[0057] Solutions of the glucans (G) used in accordance with the
invention already have a high viscosity at low concentrations, the
viscosity within the temperature range from room temperature to
approx. 140.degree. C. being substantially independent of the
temperature and substantially independent of the salt content in
the formation water (see FIG. 2 and FIG. 3). Details of this are
given in the examples section.
[0058] Flooding Medium for Process Step (B)
[0059] In process step (B), an aqueous flooding medium comprising,
as well as water, at least one glucan (G) and urea is used.
[0060] As well as water, it is optionally also possible to use
water-miscible organic solvents in small amounts, but at least 85%
by weight, preferably at least 95% by weight, of the solvents used
should be water. Preference is given to using exclusively water as
the solvent.
[0061] The water may be fresh water or else water comprising salts.
For example, the water may be seawater or partly desalinated
seawater, or all or some thereof may be salt-containing deposit
water which can be injected back into the deposit in this way.
[0062] The concentration of the glucan (G) is guided by the desired
viscosity of the flooding medium for process step (B). The
viscosity of glucan solutions at different concentrations is shown
in FIG. 1, the dependence of the viscosity as a function of
temperature in FIGS. 2 and 3.
[0063] The viscosity of the aqueous flooding medium for process
step (B) depends predominantly on the type and concentration of
glucan (G) used. It should be matched to the viscosity of the oil
phase and can be determined more accurately with the aid of the
ratio (R) between the flooding medium mobility (M.sub.w) and the
oil mobility (M.sub.o):
R=M.sub.w/M.sub.o=(k.sub.nw/.mu..sub.w)/(k.sub.nw/.mu..sub.o),
[0064] k.sub.rw--relative permeability of the formation for the
aqueous flooding medium,
[0065] k.sub.ro--relative permeability of the formation for mineral
oil,
[0066] .mu..sub.o--mineral oil viscosity,
[0067] .mu..sub.w--viscosity of the aqueous flooding medium.
[0068] .mu..sub.w relates here to the aqueous flooding medium under
use conditions in the formation. Ideally set to values <1. At
R<1, the person skilled in the art expects piston-like
displacement of the oil. The optimal ratio (R) between the water
mobility (M.sub.w) and the oil mobility (M.sub.o) is usually not
achievable, especially for highly viscous oils, because
unrealistically high injection pressures have to be developed. It
is therefore also possible to work with R values>1. However,
even a relatively small increase in the viscosity of the water
phase by means of the glucan tends to improve the mineral oil
yield.
[0069] In general, the concentration of the glucan (G) is 0.1 g/l
to 20 g/l, preferably 0.1 to 5 g/l and more preferably 0.1 to 2
g/l.
[0070] According to the invention, the aqueous formulation further
comprises urea.
[0071] Urea (H.sub.2N--CO--NH.sub.2) hydrolyzes in water at
elevated temperature to give CO.sub.2 and ammonia. By its nature,
the hydrolysis reaction is temperature-dependent, and the higher
the temperature, the more rapidly it proceeds. If the urea is
hydrolyzed under the influence of the deposit temperature in the
formation, the gases naturally form directly in the formation, and
thus foams can form in the formation.
[0072] The amount of urea in the flooding medium for execution of
process step (B) is generally 15 to 350 g/l of the formulation,
especially 15 g/l to 300 g/l, preferably 30 g/l to 250 g/l and more
preferably 50 g/l to 250 g/l.
[0073] Optionally, the formulation may further comprise at least
one ammonium salt. Examples of suitable ammonium salts comprise
ammonium nitrate and ammonium chloride in particular.
[0074] The amount of the ammonium salts in the flooding medium for
execution of process step (B) is generally 20 to 300 g/l of the
formulation, especially 20 g/l to 250 g/l, preferably 30 g/l to 250
g/l and more preferably 50 g/l to 250 g/l.
[0075] Optionally, the formulation may further comprise at least
one surfactant. Suitable surfactants for this purpose are
especially foam-forming surfactants. Foam-forming surfactants have
a certain film formation capacity and thus promote the formation of
foams. Examples of foam-forming surfactants are known in principle
to those skilled in the art. Examples comprise anionic, cationic or
nonionic surfactants, for example sulfates or sulfonates such as
alkylbenzenesulfonates, alkoxylated alkylphenols, for example
alkoxylated nonylphenols.
[0076] The amount of surfactants in the flooding medium for
execution of process step (B) is generally 0.1 to 5 g/l of the
formulation, especially 0.5 g/l to 5 g/l, preferably 1 g/l to 5 g/l
and more preferably 2 g/l to 5 g/l.
[0077] The formulation for execution of process step (B) may
additionally optionally comprise further components, for example
biocides or clay stabilizers.
[0078] To produce the formulation, urea and solid glucan (G), and
optionally further constituents, can be dissolved in water. It is,
however, advisable to use the abovementioned aqueous glucan
solution obtained from the production. The solution can be mixed
with the further components in the desired ratio and diluted to the
desired concentration. It is also possible to use the further
components in predissolved form, i.e., for example, to use an
aqueous solution of urea and mix it with an aqueous glucan (G)
solution.
[0079] Execution of Process Step (B)
[0080] To perform process step (B), the formulation mentioned is
injected into the formation through the at least one injection
well.
[0081] The flooding medium used for process step (B) is injected
into the formation with a temperature of less than 60.degree. C.,
preferably less than 35.degree. C., more preferably less than
25.degree. C. and, for example, at about room temperature. The
hydrolysis sets in at significant rate when the urea-containing
formulation has warmed up in the formation to temperatures of at
least 60.degree. C. Naturally, the rate of hydrolysis increases
with increasing temperature. Preferred temperatures for at least
one partial region of the mineral oil formation between the
injection and production wells have already been specified
above.
[0082] The NH.sub.3 and CO.sub.2 gases formed have different
effects in the formation. Some of the NH.sub.3 formed dissolves in
the water and forms an alkaline zone, and some of the CO.sub.2
formed dissolves in the oil and increases the mobility thereof. The
remaining amounts of gas form foams with the components of the
formulation for process step (B), i.e. at least the glucan (G) and
optionally the surfactants.
[0083] The process according to the invention comprising process
step (B) has the advantage that the combination of the thermally
stable and salt-stable glucan (G) with urea gives positive
synergetic effects in oil recovery. Compared to water flooding, the
level of oil recovery is not only improved in a manner known in
principle by the use of thickening polymers; instead, the
combination with urea achieves additional effects.
[0084] The hydrolysis of the urea in the mineral oil formation
forms mobile zones (banks) enriched with ammonia and CO.sub.2. The
partition coefficient of CO.sub.2 in the oil-water system is about
4 to 10 at 35-100.degree. C. and 100 to 400 bar. There is thus a
distinct accumulation of the CO.sub.2 in the mineral oil, and the
CO.sub.2 reduces the viscosity of the mineral oil in a manner known
in principle.
[0085] Furthermore, neutralization of carboxylic acids which occur
in the crude oil, for example naphthenic acid and ammonia in situ,
forms surfactants in the mineral oil deposit, which improve oil
recovery from the mineral oil formation by lowering the oil-water
interfacial tension. Naturally, these surfactant effects are
particularly advantageous in the case of mineral oils with a high
carboxylic acid content. In this process variant, it is
particularly advantageous to additionally use ammonium salts. The
ammonia formed and the ammonium ions form a buffer which keeps the
pH within a range favorable for formation of carboxylic salts.
[0086] Finally, foams form with the gases formed. The formation of
foams is supported by the glucan, since the escape of gases into
shallower zones of the mineral oil deposits is made much more
difficult by the viscous polymer solution compared to the use of
unthickened water as a flooding medium. The foam phases have a
higher viscosity than the unfoamed water phase, as a result of
which more homogeneous flooding is achieved. Gas production in the
carrier also increases the local formation pressure and hence
likewise promotes oil displacement. Since the unfoamed aqueous
urea-glucan solution has a lower viscosity than the foam, the
aqueous flooding medium after injection first of all flows through
the highly permeable zones of the formation. After foam formation,
flow through the highly permeable zones becomes much more
difficult.
[0087] Additional Process Step (A)
[0088] The process may optionally comprise at least one additional
process step (A) which is executed before a process step (B), and
in which flooding media are likewise injected into the deposit
through the injection well(s) and mineral oil is withdrawn through
at least one production well.
[0089] In one embodiment of the invention, the flooding medium is
an aqueous flooding medium (process step (A1)). This may be fresh
water or salt-containing water. For example, it may be seawater or
partly desalinated seawater, or all or some may be salt-containing
deposit water which can be injected back into the deposit in this
way.
[0090] In addition to water, it is optionally possible to use
water-miscible organic solvents, but at least 85% by weight,
preferably at least 95% by weight, of the solvents used should be
water. Preference is given to using exclusively water as the
solvent.
[0091] The aqueous flooding medium injected may have a low
temperature, for example a temperature in the range from 10.degree.
C. to 35.degree. C., or about room temperature. Such temperatures
generally arise automatically, for example are the temperature of
the seawater used for flooding. However, the flooding medium may
also be a warmed aqueous flooding medium. For example, it may be
water at a temperature of at least 80.degree. C. It may also be
superheated water, i.e. liquid water with a temperature of more
than 100.degree. C. Naturally, the pressure here is higher than 1
bar; under conditions of injection into a mineral oil formation, a
pressure of 1 bar is generally clearly exceeded.
[0092] The aqueous flooding medium for process step (A1) may, as
well as water or salt water, of course also comprise additional
components. More particularly, additional components may be
thickening components, especially thickening polymers. Preference
may be given here to a glucan (G).
[0093] The viscosity of a glucan-containing aqueous flooding medium
here should preferably be such that the viscosity of a flooding
medium injected in a process step (A1) is lower than the viscosity
of the aqueous flooding medium injected in the subsequent process
step (B).
[0094] In a further embodiment of the invention, the flooding
medium injected may be steam (process step (A2)). Steam on
injection into the mineral oil deposit may have a temperature of
more than 300.degree. C.
[0095] Additional Process Step (C)
[0096] The process may optionally comprise at least one additional
process step (C) which is executed after a process step (B), and in
which flooding media are likewise injected into the deposit through
the injection well(s) and mineral oil is withdrawn through at least
one production well.
[0097] In one embodiment of the invention, the flooding medium is
an aqueous flooding medium (process step (C1)). This may be fresh
water or salt-containing water. For example, it may be seawater or
partly desalinated seawater, or all or some may be salt-containing
deposit water which can be injected back into the deposit in this
way.
[0098] In addition to water, it is optionally possible to use
water-miscible organic solvents, but at least 85% by weight,
preferably at least 95% by weight, of the solvents used should be
water. Preference is given to using exclusively water as the
solvent.
[0099] The aqueous flooding medium injected may have a low
temperature, for example a temperature in the range from 10.degree.
C. to 35.degree. C., or about room temperature. However, the
flooding medium may also be a warmed aqueous flooding medium. For
example, it may be water at a temperature of at least 80.degree. C.
It may also be superheated water, i.e. liquid water with a
temperature of more than 100.degree. C. Naturally, the pressure
here is higher than 1 bar; under conditions of injection into a
mineral oil formation, a pressure of 1 bar is generally clearly
exceeded.
[0100] The aqueous flooding medium for process step (C1) may, as
well as water or salt water, of course also comprise additional
components. More particularly, additional components may be
thickening components, especially thickening polymers. Preference
may be given here to a glucan (G).
[0101] The viscosity of a glucan-containing aqueous flooding medium
here should preferably be such that the viscosity of a flooding
medium injected in a process step (C1) is higher than the viscosity
of the aqueous flooding medium injected in the subsequent process
step (B).
[0102] In a further embodiment of the invention, the flooding
medium injected may be steam (process step (C2)). Steam on
injection into the mineral oil deposit may have a temperature of
more than 300.degree. C.
[0103] Combination of Process Steps (A), (B) and (C)
[0104] Process steps (A), (B) and (C) can be combined with one
another. The combination may, for example, be one of the following
flooding schemes 1 to 4:
TABLE-US-00001 Flooding Process step (A1) .fwdarw. Process step (B)
.fwdarw. Process step (C1) scheme 1: Aqueous medium Aqueous medium
Flooding Process step (A2) .fwdarw. Process step (B) .fwdarw.
Process step (C2) scheme 2: Steam Steam Flooding Process step (A2)
.fwdarw. Process step (B) .fwdarw. Process step (C1) scheme 3:
Steam Aqueous medium Flooding Process step (A1) .fwdarw. Process
step (B) .fwdarw. Process step (C2) scheme 4: Aqueous medium
Steam
[0105] In addition, the sequence of process steps
(A).fwdarw.(B).fwdarw.(C) can also be repeated cyclically.
[0106] Flooding Scheme 1
[0107] In flooding scheme 1, flooding is first effected with an
aqueous flooding medium, as described above, then the flooding is
continued with the flooding medium (B) comprising glucans and urea,
and finally flooding is again effected with an aqueous flooding
medium.
[0108] In this embodiment, the natural deposit temperature should
be at least 60.degree. C., preferably at least 70.degree. C., more
preferably at least 80.degree. C. and, for example, at least
90.degree. C. It may be 60.degree. C. to 150.degree. C., especially
70.degree. C. to 140.degree. C., preferably 75.degree. C. to
135.degree. C. and more preferably 80.degree. C. to 120.degree. C.
This is because any use, in process step (A2), of cold flooding
water, i.e., for example, flooding water with a temperature in the
range from 10.degree. C. to 35.degree. C., causes the temperature
of the mineral oil deposit in the injection site environment to
fall gradually over the course of time. The flooding of a deposit
with water may take months or even years. Naturally, the cooling is
at its greatest at the injection site itself, and the temperature
again approaches the natural deposit temperature with increasing
distance from the injection site. A sufficient natural deposit
temperature ensures that the actual deposit temperature--as
required to execute the process--is at least 60.degree. C. at least
within a partial region of the mineral oil formation between the
injection and production wells.
[0109] If avoidance of cooling or at least of excessive cooling is
desired, the aqueous flooding medium can be heated before
injection, for example to temperatures of at least 80.degree.
C.
[0110] In a preferred embodiment, flooding is effected in process
step (C1) with a flooding medium which has been thickened,
preferably likewise with the aid of the glucan (G). The amount of
the glucan (G) here should be such that the viscosity of the
aqueous flooding medium injected in process step (C1) is greater
than the viscosity of the aqueous flooding medium injected in
process step (B). Such a measure counteracts the effect of
"fingering". "Fingering" means that a flooding phase of relatively
low viscosity does not form a homogeneous flow front to a flooding
phase of relatively high viscosity; instead, the flow front is
inhomogeneous. The reason for this is essentially that the
lower-viscosity flooding phase flows faster through permeable
zones, while the flow is slower through less permeable zones.
"Fingering" can be substantially avoided when the subsequent
flooding phase is more viscous.
[0111] In a further preferred embodiment, flooding is effected both
in process step (A1) and in process step (C1) with an aqueous
flooding medium which has been thickened in each case, preferably
with the aid of a glucan (G) in each case, the viscosity of the
flooding phase used increasing in the sequence
(A1).fwdarw.(B).fwdarw.(C1).
[0112] Flooding Scheme 2
[0113] In flooding scheme 2, flooding is effected first with steam,
as described above, then the flooding is continued with the
flooding medium (B) comprising glucans and urea, and finally
flooding is effected again with steam.
[0114] In this embodiment, the natural deposit temperature may also
be less than 60.degree. C. The injection of the steam in process
step (A)--the steam used for injection typically has temperatures
of up to 300.degree. C.--heats the deposit proceeding from the
injection well with increasing duration of steam injection, such
that, at least in a partial region of the mineral oil formation
between the injection and production wells, a temperature of at
least 60.degree. C., preferably at least 70.degree. C., more
preferably at least 80.degree. C. and, for example, at least
90.degree. C. is attained. It should, however, not exceed
150.degree. C., preferably 135.degree. C. and more preferably
120.degree. C. achieves. If these values are exceeded, commencement
of process step (B) should be preceded by intermediate flooding
with cold water, for example water with temperatures of 10.degree.
C. to 35.degree. C.
[0115] Subsequently, process step (B) is executed. The duration of
process step (B) can be fixed by the person skilled in the art
according to the desired results, but process step (B) is stopped
no later than when the temperature in the entire region of the
mineral oil formation between the injection and production wells
has fallen to temperatures of less than 60.degree. C. It is
advisable to stop process step (B) as soon as the temperature goes
below 70.degree. C., more preferably when it goes below 80.degree.
C.
[0116] The process is subsequently continued with the injection of
steam (process step (C2)). In order to protect the flooding phase
(B), it may also be advisable here for the injection of the steam
to be preceded by intermediate flooding with cold water. The
intermediate flood may also be thickened, preferably with the aid
of a glucan (G). If thickening is effected, the viscosity of the
intermediate flood should be at least as high as the flooding phase
used for process step (B).
[0117] Flooding Scheme 3
[0118] In flooding scheme 3, flooding is first effected with steam,
as described above, then the flooding is continued with the
flooding medium (B) comprising glucans and urea, and then the
flooding is continued with an aqueous flooding medium. The natural
deposit temperature in flooding scheme 3, as in flooding scheme 2,
may also be less than 60.degree. C. because the deposit heats up
under the influence of the steam. With regard to the details of
steps (A2) and (B), the statements for flooding scheme 2 apply.
After process step (B), process step (C1) is performed.
[0119] Flooding Scheme 4
[0120] In flooding scheme 4, flooding is effected first with an
aqueous flooding medium, as described above, then the flooding is
continued with the flooding medium (B) comprising glucans and urea,
and finally flooding is effected with steam. As in flooding scheme
1, the natural deposit temperature must be at least 60.degree. C.
Preferred temperature ranges have already been mentioned for
flooding scheme 1. In flooding scheme 4 too, it may be advisable to
follow process step (B) with intermediate flooding with cold water,
optionally thickened water.
[0121] Additional Process Step (D)
[0122] By means of additional process step (D), the process
according to the invention can be combined with "conformance
control" measures.
[0123] In mineral oil deposits with particularly heterogeneous
permeability, aqueous flooding media or else steam injected flows
preferentially through the particularly permeable regions of the
formation, from which oil is preferentially recovered as a result,
while there is less or even no flow through less permeable regions.
Thus, immobilized oil remains in the less permeable regions. This
is shown schematically in FIG. 4. An injection well (1) and two
production wells (2, 2') were sunk into a mineral oil deposit. The
aqueous flooding medium for process step (B) is injected through
injection well (1), flows in the direction of production wells (2,
2') and pushes the mineral oil onward. What is called the
displacement threshold (i.e. the boundary between the aqueous phase
and the mineral oil phase) is drawn in schematically (7). The
preferred flow paths (3) for the aqueous phase or the mobilized
mineral oil are shown by hatching. These are not straight, and
instead follow the permeable zones of the formation. Outside the
hatched area, unmobilized mineral oil remains. Also drawn in is the
60.degree. C. isotherm (4). Within the enclosed zone, it is colder;
outside the zone, it is warmer. In the regions with a temperature
from 60.degree. C., the urea begins to hydrolyze and foam formation
accordingly commences.
[0124] In step (D), in accordance with the invention, a formulation
of a thermogel thickened by means of a glucan (G) is injected, i.e.
a formulation which can form highly viscous gels after injection
under the influence of the formation temperature. The formulation
comprises at least one glucan (G), urea and at least one
water-soluble aluminum(III) salt and/or a partly hydrolyzed
aluminum(III) salt. The water-soluble aluminum(III) salts may, for
example, be aluminum chloride, aluminum bromide, aluminum nitrate,
aluminum sulfate, aluminum acetate or aluminum acetylacetonate.
They may, however, also be already partly 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 should be .ltoreq.5,
preferably .ltoreq.4.5 and more preferably .ltoreq.4. Aluminum(III)
salts are acidic, and so this pH is generally established of its
own accord given sufficient concentrations than Al(III). It would
optionally be possible to acidify somewhat further. The compounds
are preferably aluminum(III) chloride and/or aluminum(III)
nitrate.
[0125] The principle of action of such thermogels is that the
aluminum(III) salts mentioned form acidic solutions, but form
sparingly soluble gels in the alkaline range. The change in the pH
is triggered by the hydrolysis of urea at elevated temperatures, at
which ammonia forms as already outlined.
[0126] A useful amount has been found to be from 0.2 to 3% by
weight of aluminum(III), based on the aqueous formulation, and the
amount of urea should be such that 3 mol of base are released per
mole of Al(III). The rate of gel formation depends naturally on the
temperature, because the urea hydrolyzes ever more rapidly with
increasing temperature. In addition, the rate of gel formation may
depend on the aluminum(III) to urea ratio. Details of this are
compiled in the examples section.
[0127] When they reach relatively hot zones, the
aluminum-urea-glucan formulations form sparingly soluble gels. This
is shown schematically in FIG. 5; gel banks (5) have formed here.
The previously preferred flow zones are blocked as a result, and
injected flooding medium is subsequently forced to flow through
less permeable zones from which oil has yet to be recovered in the
formation. These new flow paths are shown in FIG. 5 by the arrows
(6). This allows further mineral oil to be mobilized.
[0128] The thickening of the aluminum-urea solution with the glucan
has the effect that the formulation injected, due to the increase
in viscosity, cannot mix as easily with the deposit water and with
previously injected flooding phase (B) (suppression or at least
reduction of "fingering"). In the case of excessive dilution, it
would no longer be possible for a high-viscosity gel to form. The
thickening allows the flood with the thermogel to pass through
longer distances in the formation without being diluted to too
great a degree. As a result, gel banks can also be formed at a
great distance from the injection well and the formation can thus
be blocked at these points.
[0129] Further Process Steps
[0130] The process may optionally of course comprise further
process steps. These firstly include the already mentioned
intermediate flooding with water between process steps (A) and (B)
and/or (B) and (C). In addition, the process can also be combined
with surfactant flooding. Surfactant flooding involves injection of
an aqueous formulation of surfactants into the formation, the
surfactants reducing the water-oil interfacial tension after
injection. Suitable surfactants for use in mineral oil deposits are
known to those skilled in the art and are also commercially
available. Surfactant flooding can advantageously be performed
before execution of process step (B).
[0131] One possible sequence of process steps would be, for
example, process step (A1).fwdarw.surfactant
flooding.fwdarw.process step (B).fwdarw.optionally process step
(C).
[0132] The examples which follow are intended to illustrate the
invention in detail:
[0133] Preparation of the glucan (G):
[0134] Glucan (G) with a .beta.-1,3-glycosidically Linked Main
Chain, and .beta.-1,6-glycosidically Bonded Side Groups
(Inventive)
[0135] The glucan (G) was prepared by means of the in WO
2011/082973 A2, inventive example 1, pages 15 to 16, in the
apparatus described. The concentrate obtained was diluted to the
temperature desired in each case for the tests.
[0136] Comparative Polymer 1:
[0137] Commercial synthetic polymer formed from approx. 75 mol % of
acrylamide and 25 mol % of the sulfo-containing monomer
2-acrylamido-2-methylpropanesulfonic acid (sodium salt),
weight-average molecular weight Mw of approx. 11 million g/mol
[0138] Comparative Polymer 2:
[0139] Commercial biopolymer xanthan (CAS 11138-66-2) (biopolymer
produced by fermentation with the bacterium Xanthamonas Campestris)
with a weight-average molecular weight M.sub.w of approx. 2 million
g/mol.
[0140] Comparative Polymer 3:
[0141] Commercial biopolymer diutan (biopolymer produced by
fermentation with Sphingomonas sp.) The inventive glucan and the
comparative polymers were used to perform the viscosity
measurements described hereinafter.
[0142] Performance of the Viscosity Measurements: [0143] Test
instrument: shear stress-controlled Physica MCR301 rotary
viscometer pressure cell with double-gap geometry DG 35/PR/A1
[0144] Measurement range: 25 to 170.degree. C., as specified in
each case [0145] Shear rate: as specified in each case
[0146] The complete measurement system including the syringe with
which the sample is taken and introduced into the rheometer was
purged with nitrogen. During the measurement, the test cell was
pressurized with 8 bar of nitrogen.
[0147] Test Series 1:
[0148] The viscosity of solutions of the glucan (G) (called P1 in
the figure) and of comparative polymers V1 and V2 was measured at
different concentrations of 0.2 g/l to 2 g/l. The measurements were
carried out in synthetic deposit water. For this purpose, the
polymers were dissolved in superconcentrated salt water or--in the
case that the polymer is already present as solution--a solution of
the polymer is mixed with superconcentrated salt water, and the
resulting salt solution is subsequently diluted so as to give the
concentrations stated below. The measurements of P1 and V2 were
performed at 54.degree. C., and the measurement of V1 at 40.degree.
C.
[0149] Composition of the deposit water (per liter):
TABLE-US-00002 CaCl.sub.2 42 600 mg MgCl.sub.2 10 500 mg NaCl 132
000 mg Na.sub.2SO.sub.4 270 mg NaBO.sub.2*4 H.sub.2O 380 mg Total
salinity 185 750 mg
[0150] The results are compiled in FIG. 1. FIG. 1 shows that glucan
P1 achieves the best viscosity efficiency in deposit water, i.e.
the samples give the highest viscosity at a given
concentration.
[0151] Test Series 2:
[0152] The viscosity of aqueous solutions of glucan G No. P1 and of
comparative polymers V1, V2 and V3 in ultrapure water was measured
in a concentration of in each case 3 g/l at a shear rate of 100
s.sup.-1 within the temperature range from 25.degree. C. to
170.degree. C. For this purpose, the solution of glucan (G) No. P1
was diluted correspondingly, and polymers V1, V2 and V3 were
dissolved in the corresponding concentration in water. The samples
were injected into the test cell at room temperature and the
heating rate was 1.degree. C./min. The results are shown in FIG.
2.
[0153] Test Series 3:
[0154] The procedure was as in test series 1, except that the
solutions were made up not using ultrapure water but rather
synthetic deposit water. The results are compiled in FIG. 3.
[0155] Comment for Test Series 2 and 3:
[0156] The tests show the advantages of the glucan (G) No. P1 used
in accordance with the invention compared to the comparative
polymers V1, V2 and V3 at high temperature and high salt
concentration. The viscosity of the glucan (G) No. P1 remains
constant both in salt-containing water and in ultrapure water at
temperatures of 25 to 140.degree. C., and only then begins to
decrease gradually. In ultrapure water, both the synthetic polymer
V1 (copolymer of acrylamide and
2-acrylamido-2-methylpropanesulfonic acid) and the biopolymer V3
exhibit similar behavior, while the biopolymer V2 is much worse. In
deposit water, however, all comparative polymers V1, V2 and V3 are
worse than the glucan P1 at relatively high temperatures.
[0157] Gas Formation as a Result of Decomposition of Urea
[0158] Figure shows the formation of gas bubbles of CO.sub.2 in an
aqueous solution of approx. 1.5 g/l glucan (G), 20% by weight of
urea and 3% by weight of HCI with the solutions thermostatted at
90.degree. C. The figure shows gas formation after 1, 2 and 3
h.
[0159] Formulations for Process Step (D)
[0160] For the optional process step (D), formulations composed of
water, urea and aluminum salts are used.
[0161] Table 1 below shows, by way of example, the time until gel
formation for a mixture composed of 8% by weight of AlCl.sub.3
(calculated as anhydrous product, corresponds to 1.6% by weight of
Al(III)), 25% by weight of urea and 67% by weight of water.
TABLE-US-00003 TABLE 1 Time until gel formation at different
temperatures Temperature [.degree. C.] 100 90 80 70 60 Gel
formation time [days] 1/4 1 3 6 30
[0162] Table 2 below shows the time until gel formation for various
mixtures of AlCl.sub.3 (calculated as anhydrous product), urea and
water at 100.degree. C. and 100.degree. C. It can be seen that the
time for formation of the gel becomes ever longer as the amount of
urea decreases.
TABLE-US-00004 TABLE 2 Time until gel formation ("--" no
measurement). Concentration F1 F2 of the mixture Time until gel
AlCl.sub.3 urea [% by wt.] AlCl.sub.3/urea formation [h] [% by wt.]
[% by wt.] AlCl.sub.3 urea weight ratio 100.degree. C. 110.degree.
C. 8 32 4 16 1:4 4.0 -- 8 24 4 12 1:3 4.3 -- 8 16 4 8 1:2 7.3 -- 8
8 4 4 1:1 19.0 -- 16 60 8 30 1:3.75 5.3 2 4 15 2 7.5 1:3.75 -- 8 16
48 8 24 1:3 5.5 -- 16 32 8 16 1:2 8.3 -- 16 16 8 8 1:1 18.0 -- 16
12 8 6 1:0.75 23.0 --
* * * * *