The present invention relates to a chemically enhanced oil recovery method, comprising
particularly a treatment process using ceramic membranes.
10 BACKGROUND OF THE INVENTION
Significant portions of known oil reserves are bound in formations requiring enhanced oil
recovery (EOR) techniques for effective and efficient extraction. Such reserves exist in
previously untapped fields as well as in fields where traditional oil recovery has reached a
15 practicallimit.
Among EOR techniques are steam-driven recovery methods, and non steam-driven recovery
methods. Steam-driven approaches include the Steam-Assisted Gravity Discharge (SAGD)
technique. Non steam-driven approaches include for example water flooding and chemical
flooding.
20 Water flooding comprises sweeping oil from oil-bearing formations by injecting large
volumes of water into the formations and extracting the resulting oil-water mixture topside for
processing. Generally, even after such water flooding techniques have been used on a field, at
least 40% of the Original Oil In Place (OOIP) remains in the formation.
Chemical flooding has been found useful in extracting additional oil after other techniques
25 have reached their practical limits as well as in virgin fields. Practical limits are often based
on limited water supply. While chemical flooding utilizes water, the chemical treatments
reduce water requirements, while increasing oil recovery. Chemical flooding techniques
include for example polymer flooding.
Polymer flooding comprises using specific polymers, particularly for enhancing recovery by
30 viscosity adjustment. Additional chemicals can be used, such as surfactants, (co)solvents,
alkaline compounds, and/or stabilizing compounds. While these chemicals may be used
separately in aqueous solutions, considerable experience has developed in using them in
combination in aqueous solutions. Such combination treatments are sometimes referred as
Alkali-Surfactant-Polymer (ASP) or Surfactant-Polymer (SP) treatments. For some fields,
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such treatments have been observed to result in an additional15% to 30% extraction of the
OOIP in the formation on top ofwater flooding.
Different polymer techniques have been developed for injection into subterranean oil fields. It
is known e.g. from WO 2010/133258 an aqueous solution comprising anionic or amphoteric
5 water soluble polymer and stabilizing agent for preventing the chemical degradation once the
polymer is introduced into the injection fluid.
When extracting oil using water flooding or chemical flooding techniques, there is the need
for treating the oil-water mixture extracted from the oil-bearing formations. Such treatment
processes aim first at separating the oil from the water. Such treatment processes also aim at
10 treating the produced water before being disposed of, and/or before reinjection into the
injection well as injection water.
Different oil-water mixture treatment techniques have been developed.
It is known e.g. from W020 14/151641, a method for recovering oil from an oil-bearing
formation and treating produced water containing an anti-sealant compound. Said method
15 particularly comprises the step of directing the produced water through a ceramic membrane
to remove oil from the produced water, and for obtaining a permeate stream and a retentate
stream. Prior the membrane filtration step, said method comprises several steps, including
recovering an oil-water mixture, separating oil from the oil-water mixture, deactivating the
anti-sealant compound, optionally precipitating and settling solids.
20 It is also known e.g. from W02014/151242, a process for recovering oil from an oil-bearing
formation. Said method particularly comprises the step of directing the produced water to a
ceramic membrane, for obtaining a permeate stream as well as a retentate having suspended
solids, hardness compounds, free oil and emulsified oil. Prior the membrane filtration step,
said method comprises recovering an oil-water mixture, separating oil from the oil-water
2 5 mixture, optionally carrying out an ion exchange filtration. After the membrane filtration step,
said method comprises chemically treating the permeate stream, optionally mixing a
polymeric compound with the permeate stream, optionally mixing an alkali compound with
the permeate stream, optionally mixing a surfactant compound with the permeate stream,
optionally carrying out an ion exchange filtration on the permeate stream, and injecting the
30 permeate stream into the oil-bearing formation.
Different types of ceramic membranes are known m the art. It 1s known e.g. ceram1c
membrane technologies from US5,611,931 and US6,767,455.
It is known techniques for recovering and treating oil-water mixtures, and produced water
obtained from it. The treatment of the produced water usually shows to be challenging,
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particularly considering the high viscosity of the produced water. Up to now, the techniques
for treating the produced waters, obtained from chemically enhanced oil recovery processes,
have not shown sufficiently satisfactory. Particularly, it is not known so far conventional
treatment processes for treating the produced water obtained from those processes relying on
5 the use of viscosity-increasing polymers. Indeed, known processes have shown limited
efficacy, if not at all, for separating water (in the permeate) from suspended solids, free oil,
grease and emulsified oil (in the concentrate), while allowing the recycling of the polymers.
Such processes do not usually allow obtaining a permeate, comprising the polymer. As a
consequence, such processes do not usually allow recycling most of the polymer comprised
10 into the produced water, for subsequent reinjection into the oil-bearing formation.
SUMMARY OF THE INVENTION
The present invention addresses the recovery of oil from oil-bearing geologic formations, and
15 the treatment of produced water, using an improved Chemically Enhanced Oil Recovery
(CEOR) method. It is disclosed new developments in processing the produced water from
chemical flooding EOR, for subsequent reuse of the water for enhanced oil recovery.
The present invention aims at providing a recovery method, which does not show the
20 drawbacks highlighted hereinbefore.
One goal of the present invention is providing a recovery method, which allows recycling at
least a portion of the viscosity-increasing polymeric compound, comprised into the produced
water.
Another goal of the present invention is providing a recovery method, which comprises the
2 5 treatment of the produced water using filtration means, for obtaining a permeate, in which the
polymeric compound is comprised.
Another goal of the present invention is providing a recovery method, wherein at least a
portion of the viscosity-increasing polymeric compounds, previously injected into an oilbearing
formation, is re-injected into the oil-bearing formation.
30 Another goal of the present invention is providing a recovery method, which comprises the
treatment of the produced water using filtration means, said method limiting - or even
preventing - the amount of chemicals to be added to the permeate (or the solution obtained
from it), before re-injection into the oil-bearing formation.
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The present invention relates to a chemically enhanced oil recovery method using viscosityincreasing
polymeric compounds, said recovery method comprising the steps of:
injecting an aqueous solution into an oil-bearing formation, the aqueous solution
comprising viscosity-increasing polymeric compounds;
recovering an oil-water mixture obtained from said-oil-bearing formation;
treating the oil-water mixture, for separating the oil product from the produced water,
wherein the produced water comprises the viscosity-increasing polymeric compounds;
directing the produced water to a filtration device, and subjecting the produced water
to filtration, for obtaining a retentate stream and a permeate stream, wherein the
filtration device comprises a microfiltration ceramic membrane unit having a cut-off
of from about 2!--tm to about 1 0!--tm, wherein the permeate comprises said viscosityincreasing
polymeric compounds, and wherein the permeate is substantially free of
suspended solids, free oil and emulsified oil;
injecting the permeate into the oil-bearing formation.
The inventors have surprisingly demonstrated that the goals mentioned hereinbefore could be
met by carefully selecting the type of filtration membrane to be used, and their specifics. The
inventors have shown that the filtration step allows obtaining on one hand a reject stream
comprising suspended solids, free oil, grease, and emulsified oil, and on the other hand a
20 permeate stream comprising water, and chemicals such as polymers. Such permeate has
shown to yield a sufficient amount of chemicals such as polymers, allowing its re-use for reinjection
into the oil-bearing formation, without the need for extensively treating further the
permeate, while limiting the addition of further chemicals before re-injection. Up to now, it is
believed that the known methods do not allow efficiently separating the emulsified oil and
2 5 total suspended solids from the polymer.
Such results have been obtained by selecting a filtration means being a microfiltration
ceramic membrane, and by carefully adjusting its membrane cut-off (also called "cut-off
threshold"). Indeed, the inventors has shown that the ceramic membrane shall have a cut-off
ranging from about 2!--tm to about 1 0!--tm, alternatively from about 2!--tm to about 8!--tm,
30 alternatively from about 2!--tm to about 6!--tm, alternatively from about 2!--tm to about 4!--tm,
alternatively about 3 !-tiD.
Membranes having a lower cut-off, namely ultrafiltration membranes, are usually deemed
necessary for allowing an effective separation of the oil from the water, particularly for
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allowing an effective separation of the emulsified oil from the water. In contrast, the skilled
person is usually deterred from using microfiltration membranes, i.e. membranes with a cutoff
from about 0.5!--tm, as it is expected that the emulsified oil, having typically a droplet size
ranging from about 0.5!--tm to about 20!--tm, would not be effectively separated from water,
5 leading to the obtaining of a permeate comprising at least about 1 OOppm of emulsified oil.
However, the inventors have surprisingly shown that microfiltration ceramic membranes of
lower cut-off, i.e. having a cut-off of less than 2!--tm, particularly of 1 !-tiD or less, are not
suitable for separating efficiently the emulsified oil from the polymers. It is believed that such
membranes tend to clog over time, preventing therefore the polymer to go through it, said
10 polymers being retained into the retentate, together with the oils including the emulsified oil.
In contrast, the inventors have also surprisingly shown that microfiltration ceramic
membranes of higher cut-off, i.e. having a cut-off of 2!--tm or more, particularly from 2!--tm to
about 1 0!--tm, are suitable for separating efficiently the emulsified oil and total suspended
solids from the polymers. Indeed, it has been obtained a polymer-rich permeate, only
15 comprising traces of emulsified oil i.e. about 20ppm or less of emulsified oil. Without
wishing to be bound by theory, it is believed that the emulsified oil accumulates partly into
the membrane, without passing through it, and that such accumulation drives and potentiates
the passage of the polymer, together with the water, through the membrane. Again, it is
believed that, by using a microfiltration ceramic membrane having a cut-off ranging from
20 about 2!--tm to about 1 0!--tm, the emulsified oil would act as another filtering layer into the
membrane upon accumulation, that would potentiate the filtration of the polymer through the
membrane, and therefore drives its separation from the oil.
The present recovery method allows using at least a portion of the permeate obtained after the
filtration step, for injection into the oil-bearing formation, either by direct injection or indirect
25 injection. This allows therefore re-injecting the viscosity-increasing polymeric compounds
previously injected into the oil-bearing formation, and comprised into the extracted oil-water
mixture extracted, then the separated produced water, then the filtered permeate.
The present recovery method allows therefore recycling - at least in part - the viscosityincreasing
polymeric compounds previously injected into the oil-bearing formation.
30 Consequently, it allows reducing the amount of new (or fresh or non-recycled) viscosityincreasing
polymeric compounds needed for injection into the oil-bearing formation. It allows
also adjusting the viscosity of the aqueous solution to be injected into the oil-bearing
formation.
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The permeate, comprising the viscosity increasing polymeric compound, may be injected
directly into the oil-bearing formation.
Alternatively, the permeate, comprising the viscosity increasing polymeric compound, may be
5 mixed to an aqueous solution, prior injection into the oil-bearing formation.
The permeate may be post-treated, prior injection into the oil-bearing formation. The posttreatment
may consist in the dilution of the permeate with an aqueous media.
Further compounds may be added to the permeate, prior injection into the oil-bearing
formation. The further compounds may be selected from the group consisting of further
10 viscosity increasing polymeric compounds, surfactants, solvents, alkaline compounds,
stabilizing agents, and mixtures thereof.
The produced water may be subjected to ceramic membrane filtration, at a pressure of from
about 0.5xl05 to about 5xl05 Pa. Such pressure is referred as transmembrane pressure.
The produced water may be subjected to ceramic membrane filtration, at a temperature of
15 from about 25°C to about ll0°C, preferentially from about 40°C to about 100°C.
The ceramic membrane filtration step may be carried out under a continuous feed with the
produced water.
During the ceramic membrane filtration step, a backwash of the ceramic membrane may be
carried out at regular intervals.
20 The reject stream (or a portion of it) may be disposed of. Alternatively or in parallel, the reject
stream (or a portion of it) may be recycled upstream the ceramic membrane filtration device
into the oil-water mixture (the produced water), for being further subjected to a ceramic
membrane filtration step. Alternatively or in parallel, the reject stream (or a portion of it) may
be further treated using a treatment unit, other that the ceramic membrane filtration device.
25 The ceramic membrane filtration unit may comprise a structure of at least one monolith
segments of porous material, and optionally a porous membrane.
The ceramic membrane filtration unit may be contained in a housing.
The viscosity-increasing polymeric compound may be a water-soluble polymer; alternatively
30 the viscosity-increasing polymeric compound may be selected from the group consisting of
natural water-soluble polymers, semi-synthetic water-soluble polymers, synthetic watersoluble
polymers, or mixtures thereof; alternatively the viscosity-increasing polymeric
compound may be a synthetic water-soluble polymer.
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The viscosity-increasing polymeric compound may be obtained by polymerization of
monomers selected from the group consisting of non-ionic monomers, anionic monomers,
optionally cationic monomers, optionally monomers having a hydrophobic character, and
mixtures thereof.
5 The viscosity-increasing polymeric compound may be selected from the group consisting of
non ionic polymeric compounds, anionic polymeric compounds, or mixtures therefore;
alternatively the viscosity-increasing polymeric compound may be an anionic polymeric
compound; alternatively; the anionic polymeric compounds may have an anionicity ranging
from about 10 to about 100mol%.
10
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 -A schematic representation of a method according to the invention
Figure 2 -A schematic representation of a method using a pilot unit (close loop)
15 Figure 3-A schematic representation of a method using a pilot unit (continuous feed)
Figure 4 - Graphic representation of filtrate permeability over time on an uncoated SiC
monolith ceramic membrane of water-polymer mixture comprising a poly(acrylamide-cosodium
acrylate) polymer (MW=7MDa)
Figure 5 - Graphic representation of filtrate permeability over time on an uncoated SiC
20 monolith ceramic membrane of a water-polymer mixture comprising a poly(acrylamide-cosodium
acrylate) polymer (MW=15MDa)
Figure 6 - Graphic representation of filtrate permeability/oil retention over time on an
uncoated SiC monolith ceramic membrane of an oil-water mixture comprising a 600ppm
polymer (MW 7MDa)
25 Figure 7 - Graphic representation of filtrate permeability over time on an uncoated SiC
monolith ceramic membrane of an oil-water mixture comprising a poly(acrylamide-cosodium
acrylate) polymer (MW=7MDa) at a concentration of 600ppm, oil at 1 OOOppm, TSS
at 50ppm
Figure 8 - Graphic representation of filtrate permeability over time on an uncoated SiC
30 monolith ceramic membrane of an oil-water mixture comprising a poly(acrylamide-cosodium
acrylate) polymer (MW=7MDa) at a concentration of600ppm, oil at 1000ppm, in the
absence ofTSS
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Figure 9 - Graphic representation of filtrate permeability over time on an uncoated SiC
monolith ceramic membrane of produced water comprising a polymer at a concentration of
150 ppm, TSS at a concentration of 20 to 50 ppm
5 DETAILLED DESCRIPTION
As used herein, the term "oil" means any type of oil, namely light oil, heavy oil, and/or
bituminous oil.
As used herein, the term "water-oil mixture" means the mixture, which is recovered directly
10 from the oil-bearing formation.
As used herein, the term "produced water" means the product, obtained from the water-oil
mixture, and which is separated from the oil.
As used herein, the terms "injection water", "flood water" "injection stream", and "injection
fluid" may be used interchangeably, and correspond to the aqueous solution to be injected
15 into the oil-bearing formation.
As used herein, the terms "retentate (stream)", "concentrate (stream)", and "reject (stream)"
may be used interchangeably.
As used herein, the term "substantially free" means less than about 200ppm, alternatively less
than about 1 OOppm, alternatively less than about 60ppm, alternatively less than about 40ppm,
20 alternatively it means "free".
As used here, the acronym "CEOR" means "chemically enhanced oil recovery", which is a
term conventionally used in the field of oil extraction.
In the process 100 shown in Figure 1, the produced water 12, comprising viscosity increasing
25 polymeric compounds, is directed from the oil-water separator 130 to a filtration device 140
comprising a ceramic membrane (not shown), wherein it is subjected to a filtration step. From
this filtration step, it is obtained a permeate stream 16, comprising the viscosity increasing
polymeric compounds, and a reject stream (or concentrate) 15. Prior filtration by the filtration
device 140, the produced water 13 may optionally be directed from the oil-water separator
30 130 to a pre-treatment unit 135, for obtaining a pre-treated produced water 14 (optional pretreatment
step). The pre-treated produced water 14 may then be directed from the pretreatment
unit 135 to the filtration device 140.
The produced water 12 (or 13) may be obtained from an oil-water mixture 10, which is
recovered from an oil-bearing formation 110. Indeed, an oil-water mixture 10 may be
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recovered from an oil-bearing formation 110, via a production we11120, which is in fluid
communication with the oil-bearing formation 110. The oil-water mixture 10 may be directed
from the production we11120 to an oil-water separator 130, wherein it would be subjected to
an oil-water separation step. From this separation step, it would be obtained an oil product 11,
5 which is withdrawn, and a produced water 12.
The permeate 16 may be directed from the filtration device to the injection we11160, for
injection to the oil-bearing formation 110, as an injection water 19. Prior injection into the oilbearing
formation 110 via the injection well 160, the permeate 17 may optionally be
directed from the filtration device 140 to a post-treatment unit 150, for obtaining a post-
10 treated permeate 18 (optional post-treatment step). The post-treated permeate 18 may then be
directed from the post-treatment unit 150 to the injection we11160, for injection to the oilbearing
formation 110.
15
20
Injection step
The present CEOR method comprises the step of injecting an aqueous solution into an oilbearing
formation. This step is called herein "injection step".
Aqueous solution
The aqueous solution to be injected comprises viscosity-increasing polymeric compounds and
an aqueous carrier. The aqueous carrier may be water.
The aqueous solution may have a Brookfield viscosity ranging from about 1,5mPa.s to about
600mPa.s, alternatively from about 5mPa.s to about 300mPa.s. The Brookfield viscosity is
25 made with a Brookfield viscometer at 25°C with the appropriate spindle.
The aqueous solution may comprise from about 1 OOppm to about 1 OOOOppm, alternatively
from about 200ppm to about 5000ppm, alternatively from about 500ppm to about 4000ppm
of viscosity-increasing polymeric compounds, per total of the aqueous solution.
The aqueous solution may comprise further compounds. The further compounds may be
30 selected from the group consisting on alkaline agents, surfactants, stabilizing compounds, and
mixtures thereof.
Alkaline agents
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The alkaline agent may be selected from the group consisting in alkali metal hydroxides,
ammonium hydroxides, carbonates, bicarbonates, and mixtures thereof. The alkaline agent
may be, for example, sodium carbonate.
5 Surfactants
The surfactants may be selected from the group consisting in anionic surfactants, zwitterionic
surfactants, and mixtures thereof; alternatively from the group consisting of alkyl sulfates,
alkyl ether sulfates, arylalkyl sulfates, arylalkyl ether sulfates, alkyl sulfonates, alkyl ether
10 sulfonates, arylalkyl sulfonates, arylalkyl ether sulfonates, alkyl phosphates, alkyl ether
phosphates, arylalkyl phosphates, arylalkyl ether phosphates, alkyl phosphonates, alkyl ether
phosphonates, arylalkyl phosphonates, arylalkyl ether phosphonates, alkyl carboxylates, alkyl
ether carboxylates, arylalkyl carboxylates, arylalkyl ether carboxylates, the alkyl polyethers,
arylalkyl polyethers, and mixtures thereof.
15 Presently, the term "alkyl" is understood as being a hydrocarbon group, saturated or
unsaturated, having from 6 to 24 carbon atoms, branched or unbranched, linear or optionally
comprising one or more cyclic units, which can optionally comprise one or more heteroatoms
(0, N, S). An arylalkyl group is defined as an alkyl group as defined above comprising one or
more aromatic rings, said aromatic rings optionally comprising one or more heteroatoms (0,
20 N, S).
Stabilizing compounds
The stabilizing compounds (stabilizing agents) may be compounds for suitably protecting the
25 viscosity-increasing polymeric compounds, for example against thermal, chemical and/or
mechanical degradation. Examples of suitable stabilizing agents are provided in the PCT
patent application W02010/133258, which is incorporated herein by reference.
30
Viscosity-increasing polymeric compounds
The aqueous solution, also called "injection water", comprises viscosity-increasing polymeric
compounds (herein as "polymers"). These polymers aim at enhancing recovery by viscosity
adjustment. Indeed, such polymers, when added to the aqueous solution to be injected, tend to
increase its viscosity, which improves the mobility ratio of the aqueous solution relative to
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oil. Increased viscosity of the aqueous solution may reduce viscous fingering, where thinner
aqueous solution and thicker oil results in "finger" of aqueous solution moving without
entraining the oil in the flow of aqueous solution. Increasing the viscosity of the aqueous
solution to be injected reduces this "fingering" phenomenon and results in enhanced oil
5 recovery from the formation. The polymer is typically added until its concentration in the
aqueous solution to be injected increases the viscosity up to the oil viscosity in the oil-bearing
formation. This tends to achieve a mobility ratio of closer to 1 to enable better sweep of the
oil from the rock with the water by avoiding the fingering through the oil pockets. There may
also be formation-related viscosity issues, such as permeability of the formation. Typically,
10 the oil-water mobility ratio is the controlling factor on the polymer addition when formation
permeability ranges between about lOmD to about lO,OOOmD, alternatively from 50mD and
about lO,OOOmD.
Viscosity-increasing polymeric compounds may be water-soluble polymers; alternatively they
15 may be selected from the group consisting of natural water-soluble polymers, semi-synthetic
water-soluble polymers, synthetic water-soluble polymers, or mixtures thereof.
Natural water-soluble polymers may be selected from the group consisting ofxanthan gum,
guar gum, scleroglucan, schizophillan, cellulosic derivatives such as carboxymethyl cellulose,
2 0 or mixtures thereof.
In a particular embodiment, the viscosity-increasing polymeric compound may be a synthetic,
water-soluble polymer. Synthetic, water-soluble polymers may be obtained by the
polymerization of non-ionic monomers and anionic monomers.
25 Non-ionic monomers may be selected from the group consisting of acrylamide,
methacrylamide, N-mono derivatives of acrylamide, N-mono derivatives of methacrylamide,
N ,N derivatives of acrylamide, N ,N derivatives of methacrylamide, acrylic esters, methacrylic
esters, and mixtures thereof. Preferably, the non-ionic monomer is acrylamide.
Anionic monomers may be selected from the group consisting of monomers having a
30 carboxylic function, monomers having a sulfonic acid function, monomers having a
phosphonic acid function, their salts thereof, and their mixtures thereof; alternatively from the
group consisting of acrylic acid, acrylamide tertio butyl sulfonic acid (ATBS), their salts
thereof, and mixtures thereof. Salts may be selected from the group consisting of alkaline
salts, alkaline earth salts, ammonium salts, and mixtures thereof.
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In addition of non-ionic monomers and anionic monomers, further monomers may be used,
including cationic monomers, monomers having a hydrophobic characters, and/or alternative
monomers. Water-soluble polymer may be obtained by the polymerization of at least one
non-ionic monomer, at least one anionic monomer, optionally at least one cationic monomer,
5 and/or optionally at least one monomer having a hydrophobic character in a range comprised
between about O.OOlmol% and about lmol%.
The cationic monomers may be selected from the group consisting of dimethylaminoethyl
acrylate (DMAEA) quaternized or salified, dimethylaminoethyl methacrylate (DMAEMA)
quaternized or salified, diallyldimethyl ammonium chloride (DADMAC), acrylamidopropyl
10 trimethylammonium chloride (APTAC), methacrylamidopropyl trimethylammonium chloride
(MAPT AC), and mixtures thereof.
The monomer having a hydrophobic character may be selected from the group consisting of
(meth)acrylic acid esters having an alkyl, arylalkyl or ethoxylated chain; derivatives of
(meth)acrylamide having an alkyl, arylalkyl or dialkyl chain; cationic allyl derivatives;
15 anionic or cationic hydrophobic (meth)acryloyl derivatives; anionic or cationic monomers
derivatives of (meth)acrylamide bearing a hydrophobic chain, and mixtures thereof.
20
25
Further monomers - alternative to non-ionic monomers, anionic monomers, cationic
monomers, or monomers having a hydrophobic character- may be selected for example from
N-Vinyl Pyrrolidone (NVP), AcryloyMorpholine (ACMO), or mixtures thereof.
The viscosity-increasing polymeric compounds may be linear or structured. By "structured",
it is meant a polymer not only consisting of one linear chain of moieties (i.e. polymerized
monomers), but instead a polymer having the form of a star, a comb, or a polymer having
pending groups of pending chains on the side of the main chain.
The polymerization may be carried out using any suitable polymerization technique well
known in the art. Suitable techniques include techniques comprising a polymerization step
selected from the group consisting of solution polymerization, suspension polymerization, gel
polymerization, precipitation polymerization, emulsion polymerization (aqueous or inverse)
30 or micellar polymerization, preferably selected from the group consisting of inverse emulsion
polymerization or gel polymerization.
In a preferred embodiment, the polymerization step is a free radical polymerization. By "free
radical polymerization", it is meant a polymerization step carried out in the presence of
ultraviolet irradiations, azoic initiators, redox initiators, thermal initiators, and combination
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thereof. As an alternative, controlled radical polymerization (CRP), or template
polymerization are also possible.
If necessary, the polymerization step may be followed by an isolation step, for example by
5 spray-drying or precipitation, in order to obtain a polymer powder. For example spray drying
technics are disclosed in "Spraydrying handbook", K. Masters.
The polymerization is generally a free radical polymerization preferably by inverse emulsion
polymerization or gel polymerization. By free radical polymerization, we include free radical
10 polymerization by means ofU.V. azoic, redox or thermal initiators and also Controlled
Radical Polymerization (CRP) techniques or template polymerization techniques.
The viscosity-increasing polymeric compound may be non ionic or anionic; preferably
viscosity-increasing polymeric compound having an anionicity ranging from about 1 Omol%
15 to about 1 OOmol%. Such range of anionicity is of interest for allowing potentiating the water
viscosity potential for a long time, particularly via intermolecular bonds especially when the
aqueous media is a brine
The polymer may have a molecular weight ranging from about 1 to about 30MDa, preferably
20 from about 7 to about 25 MDa.
Recovery step
The present CEOR method also comprises the step of recovering an oil-water mixture
25 obtained from the oil-bearing formation. This step is called herein "recovery step". The oilwater
mixture comprises oil, which is present originally in the oil-bearing formation, and the
aqueous solution, which is injected into the oil-bearing formation.
30
Separation step
The present CEOR method also comprises the step of treating the oil-water mixture, for
separating an oil product from a produced water. This step is called herein "separation step".
The separation step may be carried our using any suitable systems, e.g. systems comprising
separation tanks (such as those without plates and/or those with inclined-plate separators),
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hydrocyclone, system using air sparged flotation, systems using dissolved air flotation,
systems comprising wall nut shell filters, systems relying on coalescence package and filters.
Produced Water
The produced water comprises the viscosity-increasing polymeric compounds.
The produced water may have a viscosity ranging from about 1.5mPa.s to about 500 mPa.s,
alternatively from about 3 mPa.s to about 200mPa.s, alternatively from about 3 mPa.s to
about 1 OOmPa.s.
10 The produced water may have a temperature ranging from about 5°C to about l10°C,
preferably from about 40°C to about 100°C.
15
The produced water may comprise from about 50 to about 5000 ppm, preferably from about
100 to about 2000 ppm, more preferably from about 200 to about 1000 ppm of polymers, per
total of the produced water.
Filtration step
The present CEOR method also comprises the step of directing the produced water to a
filtration device, and subjecting the produced water to filtration, for obtaining a retentate
20 stream and the permeate stream. This step is called herein "filtration step".
Ceramic membrane
The filtration device comprises a microfiltration ceramic membrane (also designated as
25 microfiltration ceramic membrane unit, called herein as "filtration unit"). Upon filtration, it is
obtained a retentate stream and a permeate stream.
The filtration unit has a cut-off of from about 2!--tm to about 1 0!--tm, alternatively from about
2!--tm to about 8!--tm, alternatively from about 2!--tm to about 6!--tm, alternatively from about 2!--tm
to about 4!--tm, alternatively about 3!--tm. Such specific cut-off has shown advantageous in that
30 it allows obtaining a permeate stream comprising the viscosity-increasing polymeric
compounds. Such specific cut-off also allows obtaining a permeate being substantially free of
suspended solids, free oil and/or emulsified oil.
The permeate, obtained upon filtration, comprises the viscosity-increasing compounds.
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The permeate, obtained upon filtration, is substantially free of suspended solids, free oil and
emulsified oil.
The filtration unit may comprise a structure of at least one monolith segment of porous
5 material. The porous material, forming the monolith segments, is preferably ceramic. The
ceramic porous material may be selected from the group consisting of SiC.
Each monolith defines a plurality of passageways. The filtration unit may comprise a single
monolith segment. Alternatively, the filtration unit may comprise an assembly of monolith
segments.
10 The monolith segments may have a cross-section being circular, square, hexagonal,
rectangular, triangular, or any other suitable cross-section.
The filtration unit may also comprise a porous membrane. The porous membrane may be
applied to the walls of the monolith segment passageways. When a porous membrane is
15 present, the porous monolith acts as the porous membrane support. When present, the porous
membrane is preferably ceramic. The ceramic porous membrane may be selected from the
group consisting of SiC, Ti02, Al203 .
Alternatively, the filtration unit may not comprise a porous membrane.
20 The filtration device may comprise a housing, wherein the filtration unit is contained in a
housing. The housing may also comprise a permeate filtration zone. When present, the
permeate filtration zone may be contained in the space between filtration unit and the
housing.
25 The produced water may be subjected to ceramic membrane filtration at a pressure from about
0.5x105 to about 5x105 Pa.
30
The produced water may be subjected to ceramic membrane filtration at a temperature
ranging from about 25°C to about 11 0°C.
The ceramic membrane filtration may be carried out under a continuous feed.
During the ceramic membrane filtration step, the ceramic membrane may be backwashed.
Permeate
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The permeate, which is obtained upon filtration of the produced water, comprises the
viscosity increasing polymeric compounds. The separation step, then the filtration step have
allowed therefore recycling the viscosity increasing polymeric compounds, previously
injected into the oil-bearing formation, into the permeate.
5 The permeate further comprise an aqueous media, preferably water.
Reinjection step
The present CEOR method also comprises the step of injecting the permeate into the oil-
10 bearing formation. This step is called herein "the reinjection step".
The permeate may be injected into the same injection well, into which the aqueous solution
was previously injected (cf. injection step). Alternatively, the permeate may be injected into
different injection wells.
Depending on the implementation contemplated, the permeate may be injected directly into
15 the oil-bearing formation (direct injection); an enhanced permeate may be injected, after
having subjected the permeate to further treatments (enhancement step, then direct step); the
permeate may be mixed with a "fresh" aqueous solution, prior to injection (mixing step, then
injection step); the enhanced permeate may be mixed with a "fresh" aqueous solution, prior
injection (enhancement step, then mixing step, then injection step);the permeate is mixed with
20 fresh aqueous solution, then enhanced, then injected
Direct injection
The treated permeate may be injected directly into the oil-bearing formation. In this
25 embodiment, the aqueous solution, to be injected, consists therefore in the permeate.
30
As detailed hereinafter, whenever any enhancement step is carried out prior injection, the
enhanced permeate may be injected directly into the oil-bearing formation.
Mixing step and/or co-injection step
Prior injection into the oil-bearing, alternatively to the direct injection, the permeate may be
mixed to the aqueous solution. In this embodiment, after having mixed the permeate with the
aqueous solution, the resulting mixture would be injected into the oil-bearing formation.
16
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As detailed hereinafter, whenever any enhancement step is carried out prior injection, the
enhanced permeate may be mixed to the aqueous solution.
Pre-treatment step
After the separation step and prior to the filtration step, the present CEOR method may
further comprise a pre-treatment 135, using conventional means. Such conventional means
may be selected from:
- mechanical degradation or chemical degradation to reduce water containing viscosity;
10 -coalescence, flotation, desemulsification, hydrocyclone to increase oil droplet size; and/or,
- self-cleaning filtration set up to reduce the total suspended solid load in the stream.
Post-treatment step
15 The present CEOR method may also comprise the step of post-treating at least a portion of
the permeate. This step is called herein "post-treatment step". It is generated therefore a
treated permeate stream (also called post-treated permeate stream).
The post-treatment step may consist in the addition of an aqueous media to the permeate - in
such case the post-treatment step consists in a dilution step. The aqueous media may be water.
20 When carrying out this step, the treated permeate may also be referred as the diluted
permeate.
The dilution ratio permeate:aqueous media may range from about 1:100 to about 10:1,
preferably from about 1: 10 to about 5: 1.
In the post-treatment step, at least about 10%, alternatively at least about 25%, alternatively at
25 least about 50%, alternatively at least about 60%, alternatively at least about 70%,
alternatively at least about 80%, alternatively at least about 90%, alternatively about 100%, of
the permeate obtained upon filtration is treated.
The post-treatment step may consist in the combination of a viscosity-increasing polymeric
compound and the permeate. The purpose is to increase the viscosity of the permeate and re-
30 establish an appropriate viscosity for an injection. The type of viscosity-increasing polymeric
compound is the same as previously described. The amount of viscosity-increasing polymeric
compound may be comprised from about 1 OOppm to about 1 OOOOppm, alternatively from
about 200ppm to about 5000ppm, alternatively from about 500ppm to about 4000ppm of
viscosity-increasing polymeric compounds, per total of the permeate.
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The combination may consist in the addition of a viscosity-increasing polymeric compound in
solution form, dispersion form or particle form to the permeate. Generally, the amount of
viscosity-increasing polymeric compound added in the permeate, which contains recycled
viscosity-increasing polymeric compound, is lower than the amount of viscosity-increasing
5 polymeric compound contain in the initial injection solution.
When the viscosity-increasing polymeric compound is in particle form, it may be dissolved in
an aqueous media in a dispersing device. The permeate, or a diluted version, may be used as
the aqueous media which is used in polymer dispersing device to prepare an aqueous solution
of viscosity-increasing polymeric compound. An example of dispersing device is the Polymer
10 Slicing Unit (PSU) described in the document US 8,186,871, and which permits the
preparation of concentrated polymeric aqueous solution with viscosity-increasing polymeric
compound in powder form.
15
The post-treatment step may also consist by a polishing step such as filtration through a nut
shell filter or equivalent means.
Enhancement step
After the ceramic membrane filtration step, and before the reinjection step, the permeate (or a
portion of it) may be subjected to an enhancement step. An enhanced permeate stream would
20 be generated. The enhancement step may be carried out by adding suitable further
compounds.
Further compounds may be added to the permeate, prior injection into the oil-bearing
formation. The further compounds, to be added, may be selected from the group consisting of
further viscosity-increasing polymeric compounds, surfactants, alkaline compounds, scale
2 5 inhibitors, chelatants, stabilizers, oxygen scavengers or mixtures thereof. These compounds
have been described hereinbefore.
There may be the need for adding further viscosity-increasing polymeric compounds to the
permeate, and/or to the aqueous solution. Such further addition may be needed if:
30 (1) part of the polymeric compounds, present in the permeate, have been thermally,
chemically and/or mechanically degraded during the sweep of the oil-bearing
formation; and/or
(2) the viscosity of the aqueous solution and/or the permeate, to be injected, needs to be
adjusted.
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CEOR methods
The present invention encompasses any CEOR methods, in which the permeate is injected
5 into the oil-bearing formation. The CEOR method may be selected from the group consisting
of enhanced oil recovery process, reservoir stimulation process, sacrificial adsorption process,
or drag reduction process in water flooding.
The enhanced oil recovery (EOR) method involves a continuous and prolonged injection of a
10 solution, comprising a polymer, in order to sweep the reservoir from an injection well to a
production well. The aim is to treat not a zone of the reservoir but the totality thereof in order
to recover as much oil as possible. To that end it is necessary to inject a much greater volume
of aqueous solution, which is generally from 50% to 500%, or even more, of the pore volume.
At the production well or wells there is recovered an aqueous, oily and sometimes gaseous
15 mixture.
The reservoir stimulation method encompasses conformance process, mobility control,
plugging process, said process being characterized by injections of a solution, comprising a
polymer, which are limited in terms of volume in order to create a localized phenomenon in
20 the reservoir, namely for conformance, a sealing of zones of high permeability, for "water
shut off'', blocking zones where undesired water enters the subterranean formation. The
injections are generally carried out either by an injection well or by a production well over
quite short periods of time of several days, and generally less than one month, and with
volumes representing less than 5% of the pore volume of the reservoir. The pore volume
25 corresponds to the volume that is not occupied by the rock in the reservoir, which provides a
correlation with the permeable zone. Generally, the viscosity-increasing polymeric compound
is crosslinked with a crosslinker (organic or metallic ions) before being injected into the oilbearing
formation, or in-situ. The resulting crosslinked polymer forms a gel.
30 The sacrificial adsorption method comprises the step of a chemically enhanced oil recovery,
in which the permeate is injected into the oil-bearing formation to adsorb the polymeric
compound onto the inner surface of reservoir. The polymeric compound is adsorbed onto the
surface and acts as a sacrificial agent. This step is generally made at the beginning of a CEOR
process with a low polymeric compound concentration injection fluid and allows the
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reduction the adsorption of viscosity-increasing polymeric compound during the next
injection.
The drag reduction process during water-flooding is also considered as a chemically enhanced
5 oil recovery process because it implies the injection of the permeate. The polymeric
compound acts as a drag reducer and decreases the force (injection pressure) needed to inject
the fluid into the oil-bearing formation. Generally the drag reduction process implies the use
of a low polymeric compound concentration injection fluid.
10 EXEMPLES
Different types of ceramic membranes have been compared in order to assess their suitability
and their efficacy for separating the polymer from the oil. Particularly, it has been assessed
their suitability and their efficacy for obtaining a reject stream comprising particularly the
15 suspended solids, free oil, grease, emulsified oil; and a permeate stream comprising the
polymer.
Example 1 - Polymer concentration comparison
20 It has been tested the impact of the concentration of the polymers into the aqueous solution on
their permeability through different ceramic membranes.
The following polymers have been tested:
poly(acrylamide-co-sodium acrylate), with a molecular weight of 7MDa (herein as
2 5 "7MDa polymer"),
poly(acrylamide-co-sodium acrylate), with a molecular weight of 15MDa (herein as
"15MDa polymer").
Four different concentrations of polymer have been tested, namely 200ppm, 600ppm, 600ppm
degraded (except for the test of the 7MDa polymer on the uncoated SiC monolith membrane),
30 and lOOOppm. When applicable, the polymer is degraded by subjecting it to a high pressure,
then dropping the pressure.
The following ceramic membranes have been tested:
20
5
10
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uncoated SiC monolith ceramic membrane, having a membrane cut-off of from about
5 to about 1 0 1--lm;
standard Ti02 microfiltration ceramic membrane, having a membrane cut-off of about
0.1!--tm;
The filtrations have been carried out under the following experimental conditions:
Brine: 4830 TDS, 115 TDS divalent, 1310 TDS carbonate
Temperature: 38°C
TMP: 1bar
Concentrate velocity: 3m/s
The filtration permeability over time of 7MDa polymer on the uncoated SiC monolith ceramic
membrane is shown on figure 4. The filtration permeability over time of 15MDa polymer on
the uncoated SiC monolith ceramic membrane is shown on figure 5.
From these experiments, it is shown that the tested uncoated SiC monolith ceramic membrane
is very permeable to both 7MDa and 15MDa polymers, that the permeability decreases as the
polymer concentration increases, and that the permeability increases over time.
Except for the difference of scale as per the permeability due to the difference in cut-off,
20 similar observations are made with the tested standard Ti02 MF ceramic membrane, i.e. it is
shown that the permeability decreases as the polymer concentration increases. It has also been
shown that, for a same concentration of polymer, the permeability of the polymer is higher,
when the polymer is degraded.
25 On both membranes, it has been shown that the permeability tends to increase over time.
Without wishing to be bound by theory, it is believed that the membrane is not completely
wet (wetted) at the beginning of the experiments, and that permeability is increasing as the
membrane is getting totally wet; that the polymer is degrading slowly because of the
recirculation of both the permeate and the concentrate in the feed tank; and that the
30 concentration of the polymer is decreasing as a the test progresses.
Example 2 - Oil retention on ceramic membrane (close loop)
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It has been tested the efficacy of the permeability of the ceramic membrane, depending on the
non-continuous addition of oil.
A schematic representation of the pilot unit is shown on figure 2. In the pilot unit 200 shown
in Figure 2, the feed water is directed from the feed tank 210, via a recirculation pump 220, to
5 the filtration device 230, wherein it is subjected to filtration. From this filtration step, it is
obtained a permeate stream and a reject stream, which are both fed into the feed tank 210. A
transmembrane pressure is applied to the filtration device (not shown).
10
The following polymer has been tested:
poly(acrylamide-co-sodium acrylate ), with a molecular weight of7MDa (herein as
"7MDa polymer") at a concentration of 600ppm
The following ceramic membranes have been tested:
uncoated SiC monolith ceramic membrane, having a membrane cut-off of from about
5 to about 10!--tm
15 The filtrations have been carried out under the following experimental conditions:
20
Brine: 4830 TDS, 115 TDS divalent, 1310 TDS carbonate
Temperature: 38°C
TMP: 1bar
Concentrate velocity: 3m/s
the filtration is run for about 500min;
a backflush is carried out between about 100min and about 350min for 0,75s every
6min;
Crude oil is regularly added in the feed tank.
25 The filtration permeability over time is shown on figure 6.
It has been shown that the permeability is stable over time (between about 3500 L/(h.m2.b)
and about 4500 L/(h.m2.b )).
It has also been shown that the oil content is very low at the beginning, then reaches about
30 70 ppm at the maximum. It is apparent that this maximum concentration has been reached
after starting the backpulse. In contrast, when the backpulse is stopped, the oil concentration
decreases again to reach a value of about 13ppm.
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Without willing to be bound by theory, it is believed that the oil is absorbed by the membrane
leading to a decrease of the oil concentration in the feed tank, while the polymer is passing
through the membrane at a rate of about 90% to about 100%.
A Cleaning In Place (CIP) is carried out after each test, using a cleaning solution (surfactant
5 solution with a neutral pH). The CIP is allows cleaning the ceramic membrane, particularly by
removing from the ceramic membrane the compounds and materials accumulated onto the
monolith. The CIP allows restoring the permeability at an equivalent level of a new monolith
(filtration device).
10 Example 3- Oil retention on ceramic membrane (continuous feed)
It has been tested the efficacy of the permeability of the ceramic membrane, through a
continuous extraction of the permeate and the concentrate.
A schematic representation of the pilot unit is shown on figure 3. In the pilot unit 300 shown
in Figure 3, the feed water is directed to the feed tank 310. The feed water is then
15 continuously directed from the feed tank 310, via a recirculation pump 320, to the filtration
device 330, wherein it is subjected to filtration. From this filtration step, it is obtained a
permeate stream and a reject stream. The reject stream is directed back from the filtration
device to the feed tank 310. A transmembrane pressure is applied to the filtration device (not
shown).
20
25
The following compounds have been tested:
7MDa polymer at a concentration of 600 ppm;
Oil at a concentration of 1000 ppm;
Total Suspended Solids at a concentration of 50 ppm and with a particle size of about
100 !liD to about 150 !liD
The following ceramic membranes have been tested:
uncoated SiC monolith ceramic membrane, having a membrane cut-off of from about
5 to about 1 0 !liD
The filtrations have been carried out under the following experimental conditions:
30 Brine: 4830 TDS, 115 TDS divalent, 1310 TDS carbonate
TMP: 1bar
Concentrate velocity: 3m/s
Temperature of25°C;
23
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Continuous extraction of the permeate and the concentrate ;
Regular addition of a fresh solution into the feed tank;
The filtration permeability over time is shown on figure 7.
PCT/EP2015/073490
It has been shown that the permeability is decreasing over time, although there is no
concentration of the feed during the test. Without willing to be bound by theory, it is believed
that such decrease can be due to the accumulation of oil into the membrane, in combination
with a lower temperature than for the tests reported hereinbefore, which impairs the passage
10 of the water through the membrane, and therefore impairs the passage of the polymers
through the membrane.
The permeability can be recovered after cleaning with various cleaning solutions, such
surfactant solution with a neutral pH, citric acid and sodium hypochlorite (not shown).
15 Example 4- Oil retention on ceramic membrane (continuous feed)
It has been tested the efficacy of the permeability of the ceramic membrane, through a
continuous extraction of the permeate and the concentrate. A schematic representation of the
pilot unit is shown on figure 3
20 The following compounds has been tested:
7MDa polymer at a concentration of 600ppm;
Oil at a concentration of 1 OOOppm;
NoTSS
The following ceramic membranes have been tested:
2 5 uncoated SiC monolith ceramic membrane, having a membrane cut-off of from about
5 to about 10!--tm
30
The filtrations have been carried out under the following experimental conditions:
Brine: 4830 TDS, 115 TDS divalent, 1310 TDS carbonate
TMP: 1bar
Concentrate velocity: 3m/s
Temperature of 40°C
Continuous extraction of the permeate and the concentrate;
24
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Regular addition of a fresh solution into the feed tank at times 13, 21, 32, 48, 65, 85,
105 and 130 min
The filtration permeability over time is shown on figure 8.
It has been shown that the permeability is decreasing slowly during the first part of the test,
while it remains stable at a lower value during the second part of the test. Without willing to
be bound by theory, it is believed that, during the first part of the test, oil is accumulating
inside the membranes leading to a decrease of permeability. However, after some time, a
10 steady state is reached wherein the accumulated oil is creating another filtering layer with a
constant permeability. The oil concentration in the permeate appears to be stable, at a value of
around 20ppm. In contrast, the oil concentration in the retentate is not stable, which is
believed to be due to the addition of feed batch by batch in the feed tank. An alternative or
complementary explanation could be that the increase in concentration can also be due to the
15 accumulation and release of oil by the membrane.
The permeability can be recovered after cleaning twice the membrane device with a surfactant
solution with a neutral pH (not shown).
Example 5 - Treatment of real Produced Water (closed loop)
20 It has been tested the efficacy of the permeability of the ceramic membrane, through a
recirculation loop of the permeate and the concentrate. A schematic representation of the pilot
unit is shown on figure 2.
The produced water with the following composition has been tested:
25 a polymer at a concentration of 150ppm;
TSS at a concentration of about 20 to 50ppm;
The following ceramic membranes have been tested:
uncoated SiC monolith ceramic membrane, having a membrane cut-off of from about
5 to about 1 0 !liD
30 The filtrations have been carried out under the following experimental conditions:
TMP: 1bar
Concentrate velocity: 3m/s
Temperature of 35°C
Recirculation of the permeate and the concentrate (closed loop);
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For one of the trails, operation in dead-end mode for 5 min at 19, 30, 47, 58 min.
The filtration permeability over time is shown on figure 9.
5 It has been shown that the permeability is decreasing slowly during the first part of the test,
while it remains stable at a lower value during the second part of the test.
Example 6 - Chemical Enhanced Oil Recovery Process
A Chemical Enhanced Oil Recovery process is simulated with a coreflood system by injecting
10 an aqueous solution comprising a poly(acrylamide-co-sodium acrylate) having a molecular
weight of 15MDa (step 1). The produced water is filtrated with a ceramic membrane
according to the invention to obtain a permeate (step 2), and the permeate is used to prepare a
new aqueous solution in which fresh polymer is dissolved (step 3). Finally the resulted
aqueous solution is injected (step 4).
15
20
25
30
Step 1 -Injection of an aqueous solution comprising a poly(acrylamide-co-sodium acrylate)
(15MDa)
A core flow injection with the following characteristics is performed:
Temperature: 50°C
Average permeability: 1200 mD sandstone
Oil gravity : 22° API.
The aqueous solution comprising the polymer has the following composition and properties :
NaCl : 3300 mg/L
KCl: 70 mg/L
CaC12, 2H20 : 150 mg/L
Mg,Cl2, 6H20 : 85 mg/L
Na2S04 : 30 mg/L
NaHC03 : 100 mg/L
Dissolved Oxygen : 20 ppb
Total suspended solids: 5 ppm
pH: 7,5
Polymer concentration : 1000 ppm
Viscosity : 25 cP
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Filter ratio : 1,1
The recovery factor is 38 %.
Without the addition of 1000 ppm of polymer, the recovery factor is only 25%.
5 Step 2 - Filtration of the produced water with a ceramic membrane according to the invention
On the produced water side of the core flow, polymer is produced along with the water. The
produced water comprising the polymer has the following characteristics:
10
15
20
25
30
NaCl : 3000 -3500 mg/L
KCl: 50-100 mg/L
CaC12, 2H20: 120-170 mg/L
Mg,Cl2, 6H20: 60-100 mg/L
Na2S04: 25-40 mg/L
NaHC03: 40-100 mg/L
Dissolved Oxygen : 20 ppb
pH: 7,5
Total suspended solids: 10-15 ppm with average size of 10 11m
Oil in water concentration : 300-700 ppm with average size of 12,5 11m
Polymer concentration: 500 ppm
Viscosity : 3,5 cP
The produced water is filtrated on a uncoated SiC monolith ceramic membrane, having a
membrane cut-off of from about 5 to about 1 0!--tm, and a permeate is obtained, which has the
following characteristics :
Polymer concentration: 500 ppm
NaCl : 3000 -3500 mg/L
KCl: 50-100 mg/L
CaC12, 2H20: 120-170 mg/L
Mg,Cl2, 6H20: 60-100 mg/L
Na2S04: 25-40 mg/L
NaHC03 : 40-100 mg/L
Dissolved Oxygen : 20 ppb
pH: 7,5
Total suspended solids: 5 ppm with average size of 10 11m
Oil in water concentration : 5-20 ppm
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Polymer concentration: 500 ppm
Viscosity : 3,5 cP
PCT/EP2015/073490
The polymer initially contained in the produced water is present in the permeate and may be
5 recycled for a new injection.
Step 3- Preparation of new viscosified aqueous solutions for injection
Two different aqueous solutions are prepared with the permeate.
10 New aqueous solution A is obtained by dissolving in the permeate 1000 ppm of freshly added
poly(acrylamide-co-sodium acrylate) (15MDa). The viscosity obtained is 32 cP and the Filter
ration is 1,1
New aqueous solution B is obtained by dissolving in the permeate 700 ppm of freshly added
poly(acrylamide-co-sodium acrylate) (15MDa). The viscosity obtained is 25 cP and the Filter
15 ratio is 1,1
20
25
Step 4- Injection of new viscosified aqueous solution A and B
The same coreflow of step 1 is made with new viscosified aqueous solutions A and B. The
following recovery factors are obtained.
new viscosified aqueous new viscosified aqueous
solution A solution B
Recovery factor 43% 38%
The process of the invention has the advantage to recycle a part of the polymer for new
injection. One may reduce the polymer consumption (1000 ppm to 700 ppm) to obtain the
same recovery factor, or one may increase the recovery factor (38% to 43%) while
maintaining the same polymer consumption (1 000 ppm).
28

CLAIMS
1. A chemically enhanced oil recovery method using viscosity-increasing polymeric
compounds, said recovery method comprising the steps of:
injecting an aqueous solution into an oil-bearing formation, said aqueous solution
comprising viscosity-increasing polymeric compounds;
recovering an oil-water mixture obtained from said oil-bearing formation;
treating the oil-water mixture, for separating an oil product from a produced water,
wherein the produced water comprises the viscosity-increasing polymeric compounds;
directing the produced water to a filtration device, and subjecting the produced water
to filtration, for obtaining a retentate stream and a permeate stream, wherein the
filtration device comprises a microfiltration ceramic membrane unit having a cut-off
of from about 2!--tm to about 10!--tm, wherein the permeate comprises said viscosityincreasing
polymeric compound, and wherein the permeate is substantially free of
suspended solids, free oil and emulsified oil;
injecting the permeate into the oil-bearing formation.
2. The recovery method of claim 1, wherein the permeate is injected directly into the oilbearing
formation.
3. The recovery method of any preceding claims, wherein it further comprises the step if
post-treating the permeate, prior injection into the oil-bearing formation; alternatively
wherein it further comprises the step of diluting the permeate with an aqueous media.
25 4. The recovery method of claim 1, wherein the permeate is mixed to the aqueous
30
solution, prior injection into the oil-bearing formation.
5. The recovery method of any preceding claims, wherein further compounds are added
to the permeate, prior injection into the oil-bearing formation.
6. The recovery method of claim 4, wherein the further compounds are selected from the
group consisting of further viscosity-increasing polymeric compounds, surfactants,
alkaline compounds, stabilizing agents, and mixtures thereof.
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7. The recovery method according to any preceding claims, wherein the produced water
is subjected to ceramic membrane filtration at a pressure of from about 0.5x105 to
about 5x105 Pa.
5 8. The recovery method according to any preceding claims, wherein the produced water
10
15
is subjected to ceramic membrane filtration at a temperature of from about 25°C to
about 11 0°C.
9. The recovery method according to any preceding claims, wherein the ceramic
membrane filtration is carried out under a continuous feed.
10. The recovery method according to any preceding claims, wherein the microfiltration
ceramic membrane is backwashed at regular intervals, during the ceramic membrane
filtration step.
11. The recovery method according to any preceding claims, wherein the ceramic
membrane filtration unit comprises a structure of at least one monolith segment of
porous material, and optionally a porous membrane.
20 12. The recovery method according to any preceding claims, wherein the ceramic
25
membrane filtration unit is contained in a housing.
13. The recovery method according to any preceding claims, wherein the viscosityincreasing
polymeric compound is a water-soluble polymer, alternatively wherein the
viscosity-increasing polymeric compound may be selected from the group consisting
in natural water-soluble polymers, semi-synthetic water-soluble polymers, synthetic
water-soluble polymers, or mixtures thereof; alternatively wherein the viscosityincreasing
polymeric compound is a synthetic, water-soluble polymer.
30 14. The recovery method according to any preceding claims, wherein the viscosityincreasing
polymeric compound is obtained by polymerization of non-ionic monomers
anionic monomers, optionally cationic monomers, optionally monomers having a
hydrophobic character.
30
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15. The recovery method according to any preceding claims, wherein the viscosityincreasing
polymeric compound may be selected from the group consisting of non
ionic polymeric compounds, anionic polymeric compounds, or mixtures therefore;
preferably anionic polymeric compounds; more preferably anionic polymeric
compounds having an anionicity ranging from about 10 to about 100mol%.