WO2016139302A1

WO2016139302A1 - Polymer-containing oil recovery formulation

Info

Publication number: WO2016139302A1
Application number: PCT/EP2016/054535
Authority: WO
Inventors: Gerardus GLASBERGEN; Volodimir Mikolajovitsj KARPAN; Mark Michael SHUSTER; Diego WEVER
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2015-03-04
Filing date: 2016-03-03
Publication date: 2016-09-09

Abstract

A process of preparing polymer containing oil recovery formulation having a pH of at least 8 which process comprises adding polymer and alkali to water and a process for oil production comprising injecting an oil recovery formulation thus prepared into an oil formation.

Description

POLYMER-CONTAINING OIL RECOVERY FORMULATION

The present invention relates to a process for preparing an oil recovery formulation and to a process for oil production comprising injecting an oil recovery formulation thus prepared into an oil containing

formation .

In the recovery of oil from a subterranean formation, only a portion of the oil in the formation generally is recovered using primary recovery methods utilizing the natural formation pressure to produce the oil. A portion of the oil that cannot be produced from the formation using primary recovery methods may be produced by chemical enhanced oil recovery, also referred to as improved oil recovery or EOR.

One enhanced oil recovery method utilizes polymer or a combination of surfactant and polymer to flood an oil- bearing formation to increase the amount of oil recovered from the formation. An aqueous dispersion of a polymer and optionally a surfactant is injected into an oil- bearing formation to increase recovery of oil from the formation, either after primary recovery or after a secondary recovery water flood. Without wishing to be bound by any theory, it is thought that the polymer is present to increase the viscosity of the enhanced oil recovery oil recovery formulation, preferably to the same order of magnitude as the oil in the formation in order to force the mobilized oil through the formation for production by the polymer containing flood. If surfactant is present, the surfactant is thought to enhance recovery of oil from the formation by lowering interfacial tension between oil and water phases in the formation thereby mobilizing the oil for production. It was found that the wells can become blocked when applying polymer containing oil recovery formulations . In some cases, this is attributed to the presence of undissolved material in the enhanced oil recovery solution. Dissolving the polymer is not trivial due to the inherent low entropy of mixing of high molecular weight polymers. Undissolved material could be removed with the help of an additional filtration step. However, it would be highly advantageous if such additional filtration step is not required. Furthermore, it was found that the filters used in the filtration sometimes became blocked as well.

Therefore, it is desired to change the properties of the polymer containing oil recovery formulation such that there is less plugging of the formation during injection without using an additional filtration step.

It was surprisingly found that it was possible to reduce plugging by preparing polymer containing oil recovery formulation by the process of the present invention.

The present invention relates to a process of preparing polymer containing oil recovery formulation having a pH of at least 8 which process comprises adding polymer and alkali to water. These polymer containing solutions can be used in various applications in oil recovery such as in hydraulic fracturing and shutting off water-bearing channels or fractures within the formation to prevent water from making its way to the well, also referred to as water shut off. Preferably, the polymer containing formulations of the present invention are used in enhanced oil recovery.

The present invention furthermore relates to a process for oil production which process comprises injecting into an oil containing formation a polymer containing oil recovery formulation prepared according to the present invention. Preferably, water has been injected into the oil containing formation prior to injecting the polymer containing oil recovery formulation of the present invention. The oil can be any hydrocarbon composition present in the formation.

The expression water is used to indicate any source of water including but not limited to fresh water generally containing traces of contaminants up to sea water and brine containing substantial amounts of such contaminants .

If pure water is used, the formulation consists of water, polymer and alkali. Pure water is considered to be water having a total dissolved solids content (TDS, measured according to ASTM D5907) of at most 4000 ppm, more specifically at most 3000 ppm, more specifically at most 2000 ppm, most specifically at most 1000 ppm. The expression "ppm" indicates parts per million by weight on total weight amount present.

Water sources other than pure water are sea water, brackish water, aquifer water, formation water and brine. Sources other than fresh water generally have a TDS of more than 1,000 ppm, more specifically at least 2,000 ppm, more specifically at least 3,000 ppm, more

specifically at least 4,000 ppm, more specifically at least 5,000 ppm, most specifically at least 10,000 ppm. Most water sources have a TDS of less than 100,000 ppm, more specifically less than 80,000 ppm, more specifically at most 60,000 ppm, most specifically at most 40,000 ppm.

These amounts are before alkali and polymer and

optionally surfactant have been added.

The source of water used in the present invention preferably has a reduced ionic strength namely of 0.15 M or less. The water source preferably has an ionic strength of at most 0.1 M or at most 0.05 M, or at most 0.01 M, and may have an ionic strength of from 0.01 M to 0.15 M, or from 0.02 M to 0.125 M, or from 0.0 3M to 0.1

M. Ionic strength, as used herein, is defined by the equation

I=½*∑₁₌i ⁿ C i Z i where I is the ionic strength, c is the molar

concentration of ion i, z is the valency of ion i, and n is the number of ions in the measured solution. Such aqueous solution including its preparation is described in WO-A-2014/0041856. Such water source is especially suitable for use with polymers developed for use in a low salinity environment .

It is especially advantageous if the water used for preparing the formulation contains a limited amount of divalent ions such as less than 4000 ppm, more

specifically less than 2000 ppm, more specifically less than 1000 ppm, more specifically at most 500 ppm, more specifically at most 100 ppm, most specifically at most 20 ppm of divalent ions based on total amount of water. More specifically, these amounts relate to the calcium and/or magnesium containing salts.

In a preferred embodiment, the formulation is prepared by adding a mixture of alkali and polymer, more preferably a solid mixture of alkali and polymer. The mixtures are easy to handle and store while they still give a formulation having improved filterability

properties .

The formulation according to the invention can be prepared by first manufacturing a solid mixture of polymer and alkali off site and subsequently transporting the mixture to and preparing the mother liquor, maturing and diluting it at the site at which it is to be used in oil recovery.

If the formulation is prepared with the help of a mother liquor, it is preferred that alkali and polymer are added to water, the solution obtained is allowed to mature and the matured solution is diluted by adding a source of water, preferably a source having a TDS of at least 3,000 up to at most 80,000 ppm. A specifically preferred embodiment comprises preparing mother liquor with the help of a source of water having reduced ionic strength and/or limited divalent ion content as described above. The maturation is carried out by allowing the solution to develop for a time period of at least 0.5 hour, more specifically more than 1 hour. Without wishing to be bound to any theory, it is thought that the polymer further dissolves during this time. The solution

preferably is stirred during maturation. In commercial operation, maturation generally takes place for at most 10 hours. Research may allow for longer maturation times such as up to 72 hours for convenience or to make sure chemical equilibrium has been reached. Maturation times can be shortened by specific treatments for improving dissolution of the polymer such as treating the solution with a polymer slicing unit commercially available from the company EP MECA. If maturation is carried out with intense mixing, the maturation time period can be of from 0.25 to 4 hours, more specifically of from 0.5 to 2 hours .

The alkali used for preparing the formulation can be a single compound or be a mixture of compounds. Preferably, the alkali is selected from the group consisting of trimethylamine , triethylamine , ammonia, ammonium hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium

bicarbonate, potassium bicarbonate, lithium silicate, sodium silicate, potassium silicate, lithium phosphate, sodium phosphate, potassium phosphate, and mixtures thereof. More preferably, the alkali used is selected from the group consisting of trimethylamine,

triethylamine, ammonia, sodium carbonate, ammonium hydroxide and sodium hydroxide. Most preferably, the alkali used is selected from the group consisting of sodium carbonate, ammonium hydroxide and sodium

hydroxide.

The preferred pH of the formulation depends on the type and concentration of the polymer to be dissolved and the formation into which the formulation is to be injected. The pH of the formulation is to be at least 8, preferably is at least 8.2, more specifically is at least

8.4. Preferably, the formulation has a pH of at most 13, more specifically at most 12.5, more specifically at most 12, most specifically less than 12. In order to prevent damage to the formation, the formulation to be injected into the formation preferably has a pH of at most 12, more specifically at most 11, most specifically at most 10.5.

The polymer present in the oil recovery formulation generally is intended to provide the formulation with a viscosity of the same order of magnitude as the viscosity of oil in the formation under formation temperature conditions so the oil recovery formulation may drive mobilized oil across the formation for production from the formation with a minimum of fingering of the oil through the oil recovery formulation and/or fingering of the oil recovery formulation through the oil. The polymer can be a single compound or can be a mixture of

compounds. Preferably, the polymer is selected from the group consisting of polyacrylamide ; partially hydrolyzed polyacrylamide ; polyacrylate ; ethylenic co-polymer;

carboxymethylcelloluse ; polyvinyl alcohol; polystyrene sulfonate; polyvinylpyrrolidone; biopolymers; 2- acrylamide-methyl propane sulfonate (AMPS) ; styrene- acrylate copolymer; co-polymers of acrylamide, acrylic acid, AMPS and n-vinylpyrrolidone in any ratio; and combinations thereof.

Examples of ethylenic co-polymers include co-polymers of acrylic acid and acrylamide, acrylic acid and lauryl acrylate, and lauryl acrylate and acrylamide. Examples of biopolymers include xanthan gum, guar gum, schizophyllan and scleroglucan .

Most preferably, the polymer is (hydrolyzed)

polyacrylamide. The latter includes but is not limited to copolymers of acrylamide and acrylic acid or sodium acrylate such as polymers which are being sold by SNF under the name Flopaam 3630S, Flopaam 6030S and Flopaam EM533.

The concentration of the polymer in the mother liquor may be substantially higher than the concentration of the oil recovery formulation actually injected into the formation. The concentration of polymer in this mother liquor can be of from 80 to 80,000 ppm, more specifically of from 1250 to 50000 ppm, more specifically of from 2500 to 25000 ppm, most specifically of from 5000 to 10000 ppm based on total amount of mother liquor.

The concentration of the polymer in the oil recovery formulation to be injected into the formation preferably is sufficient to provide the oil recovery formulation with a dynamic viscosity of at least 0.3 mPa s (0.3 cP), more specifically at least 1 mPa s (1 cP), or at least 10 mPa s (10 cP), or at least 100 mPa s (100 cP), or at least 1000 mPa s (1000 cP) at 25°C or at a temperature within a formation temperature range. The concentration of polymer in the oil recovery formulation preferably is from 250 ppm to 10000 ppm, or from 500 ppm to 5000 ppm, or from 1000 to 2000 ppm based on total amount of formulation .

The molecular weight number average of the polymer in the oil recovery formulation preferably is at least 10000 daltons, or at least 50000 daltons, or at least 100000 daltons. The polymer preferably has a molecular weight number average of from 10000 to 30000000 daltons, or from 100000 to 15000000 daltons.

The oil recovery formulation may also comprise co- solvent with water, where the co-solvent may be a low molecular weight alcohol including, but not limited to, methanol, ethanol, and iso-propanol, isobutyl alcohol, secondary butyl alcohol, n-butyl alcohol, t-butyl alcohol, or a glycol including, but not limited to, ethylene glycol, 1 , 3-propanediol, 1 , 2-propandiol , diethylene glycol butyl ether, triethylene glycol butyl ether, or a sulfosuccinate including, but not limited to, sodium dihexyl sulfosuccinate . The co-solvent may be utilized for assisting in prevention of formation of a viscous emulsion. If present, the co-solvent preferably is present in an amount of from 100 ppm to 50000 ppm, or from 500 ppm to 5000 ppm of the total oil recovery formulation. A co-solvent may be absent from the oil recovery formulation. The oil recovery formulation may additionally contain paraffin inhibitor to inhibit the formation of a viscous paraffin-containing emulsion in the mobilized oil by inhibiting the agglomeration of paraffins in the oil. The mobilized oil, therefore, may flow more freely through the formation for production relative to mobilized oil in which paraffins enhance the formation of viscous

emulsions. The paraffin inhibitor of the oil recovery formulation may be a compound effective to inhibit or suppress formation of a paraffin-containing emulsion. The paraffin inhibitor may be a compound effective to inhibit or suppress agglomeration of paraffins to inhibit or suppress paraffinic wax crystal growth in the oil of the formation upon contact of the oil recovery formulation with the oil in the formation. The paraffin inhibitor may be any commercially available conventional crude oil pour point depressant or flow improver that is dispersible, and preferably soluble, in the fluid of the oil recovery formulation in the presence of the other components of the oil recovery formulation, and that is effective to inhibit or suppress formation of a paraffin-nucleated emulsion in the oil of the formation. The paraffin inhibitor may be selected from the group consisting of alkyl acrylate copolymers, alkyl methacrylate copolymers, alkyl acrylate vinylpyridine copolymers, ethylene vinylacetate copolymers, maleic anhydride ester

copolymers, styrene anhydride ester copolymers, branched polyethylenes , and combinations thereof.

Commercially available paraffin inhibitors that may be used in the oil recovery formulation include HiTEC

5714, HiTEC 5788, and HiTEC 672 available from Afton Chemical Corp; FLOTRON D1330 available from Champion Technologies; and INFINEUM V300 series available from Infineum International.

The paraffin inhibitor may be present in the oil recovery formulation in an amount of from 5 ppm to 5000 ppm, or from 10 ppm to 1000 ppm, or from 15 ppm to 500 ppm, or from 20 ppm to 300 ppm based on total amount of formulation .

The oil recovery formulation may further comprise a surfactant, where the surfactant may be any surfactant effective to reduce the interfacial tension between oil and water in the oil-bearing formation and thereby mobilize the oil for production from the formation. The oil recovery formulation may comprise one or more surfactants. The surfactant may be an anionic surfactant. The anionic surfactant may be a sulfonate-containing compound, a sulfate-containing compound, a carboxylate compound, a phosphate compound, or a blend thereof. The anionic surfactant may be an alpha olefin sulfonate compound, an internal olefin sulfonate compound, a branched alkyl benzene sulfonate compound, a propylene oxide sulfate compound, an ethylene oxide sulfate compound, a propylene oxide-ethylene oxide sulfate compound, or a blend thereof.

The anionic surfactant preferably contains from 12 to 28 carbons, or from 12 to 20 carbons. The surfactant of the oil recovery formulation may comprise an internal olefin sulfonate compound containing from 15 to 18 carbons or a propylene oxide sulfate compound containing from 12 to 15 carbons, or a blend thereof, where the blend contains a volume ratio of the propylene oxide sulfate to the internal olefin sulfonate compound of from 1:1 to 10:1.

The oil recovery formulation may contain an amount of the surfactant effective to reduce the interfacial tension between oil and water in the formation and thereby mobilize the oil for production from the

formation. The oil recovery formulation may contain from 0.05 wt . % to 5 wt . % of the surfactant or combination of surfactants, or may contain from 0.1 wt . % to 3 wt . % of the surfactant or combination of surfactants based on total amount of formulation.

The alkali present in the oil recovery formulation may not only aid in dissolving the polymer but may also interact with oil in the formation to form a soap effective to reduce the interfacial tension between oil and water in the formation. The alkali added for this purpose can be incorporated in the formulation before or after or simultaneous with the polymer and preferably is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, lithium

bicarbonate, sodium bicarbonate, potassium bicarbonate, lithium silicate, sodium silicate, potassium silicate, lithium phosphate, sodium phosphate, potassium phosphate, and mixtures thereof.

The amount of the alkali effective to interact with the oil in the formation to form a soap effective to reduce the interfacial tension between oil and water in the formation and thereby mobilize the oil for production from the formation preferably is of from 0.001 wt . % to 5 wt . % of the alkali, or from 0.005 wt . % to 1 wt . % of the alkali, or from 0.01 wt . % to 0.5 wt . % of the alkali based on total amount of enhanced oil recovery formulation.

The oil recovery formulation to be injected into the formation preferably has a pH of at least 8 and a TDS of from 80 to 60,000 ppm; and from 100 to 40,000 ppm, more specifically from 250 ppm to 10,000 ppm, or from 500 ppm to 5,000 ppm, or from 1000 to 2000 ppm of polymer or a combination of polymers based on total amount of

formulation .

In a preferred method of the present invention, the oil recovery formulation is introduced into an oil- bearing formation or oil formation. The oil contained in the oil-bearing formation may have a dynamic viscosity under formation conditions (in particular, at

temperatures within the temperature range of the

formation) of at least 0.3 mPa s (0.3 cP), more

specifically at least 1 mPa s (1 cP), or at least 10 mPa s (10 cP), or at least 100 mPa s (100 cP), or at least 1000 mPa s (1000 cP), or at least 10000 mPa s (10000 cP). The oil contained in the oil-bearing formation may have a dynamic viscosity under formation temperature conditions of from 1 to 10000000 mPa s (1 to 10000000 cP) .

The following exemplifies the present invention but is not intended to limit, or define, the scope of the current invention.

EXAMPLES

The experiments were carried out at ambient

temperature. Solutions were prepared by mixing polymer and alkali (each as a solid) and adding this mixture to fresh water which was stirred at a speed of 300 rounds per minute in standard glass laboratory equipment. Care was taken that no agglomerates were formed during addition of the mixture.

The solutions tested for filterability in Example 5 (both those prepared not according to the invention and those prepared according to the invention) had similar viscosity which did not hamper filtration.

Flopaam 3230s is commercially available partially hydrolyzed polyacrylamides available from SNF Floerger. Example 1

10,000 ppm of Flopaam 3230s polyacrylamide was added to demineralized water and stirred (matured) for 1 hour. The solution obtained had neutral pH. This solution was diluted with an aqueous solution containing 2.625 %wt of sodium chloride (26,250 ppm of NaCl) in demineralized water in a weight ratio of polyacrylamide solution to sodium chloride solution of 1:4. This is Solution A, not according to the invention.

Example 2

Example 1 was repeated with the exception that stirring (maturation) was carried out for 48 hours. The solution obtained after dilution is referred to as Solution B, not according to the invention.

Example 3

10,000 ppm of Flopaam 3230s polyacrylamide was mixed with 0.25 %wt sodium carbonate (2,500 ppm Na2C03) in the solid state. This mixture was added to demineralized water and stirred (matured) for 1 hour. This solution was diluted with an aqueous solution containing 2.625 %wt of sodium chloride (26,250 ppm of NaCl) in demineralized water in a weight ratio of polyacrylamide solution to sodium chloride solution of 1:4. The solution obtained had a pH of 8.5. This is Solution 1 according to the invention. Example 4

Example 3 was repeated with the exception that stirring (maturation) was carried out for 19 hours. The solution obtained after dilution is referred to as Solution 2, according to the invention.

Example 5

Each of the above solutions were filtered with the help of an Isopore polycarbonate filter having openings of 1.2 microns and having a diameter of 47 mm which filter is commercially available from Millipore. Filtration was carried out at a constant pressure of 2 bar.

The time required for 20 g of solution to pass the filter close to the end of the filtration (t200g - tl80g) is divided by the time required for 20 g of solution to pass the filter at the start of the filtration (t80g - t60g) . This ratio is termed the Filtration Ratio (FR) .

The following Filtration Ratios were measured for the various solutions.

Table 1

Sol. A Sol . Sol . Sol.2

B 1

Filtration Ratio 1.64 1.67 1.44 1.12

Claims

C L A I M S

1. A process of preparing polymer containing oil recovery formulation having a pH of at least 8 which process comprises adding polymer and alkali to water.

2. Process according to claim 1 in which the polymer is selected from the group consisting of polyacrylamide; partially hydrolyzed polyacrylamide; polyacrylate ;

ethylenic co-polymer; carboxymethylcelloluse ; polyvinyl alcohol; polystyrene sulfonate; polyvinylpyrrolidone; biopolymers; 2-acrylamide-methyl propane sulfonate

(AMPS) ; styrene-acrylate copolymer; co-polymers of acrylamide, acrylic acid, AMPS and n-vinylpyrrolidone in any ratio; and combinations thereof.

3. Process according to claim 2 in which the polymer is (hydrolyzed) polyacrylamide.

4. Process according to any one of claims 1 to 3 in which a mixture of polymer and alkali is added to water having a total dissolved solids content (TDS, measured according to ASTM D5907) of from 3,000 to at most 60,000 ppm .

5. Process according to any one of claims 1 to 3 which comprises adding alkali and polymer to water, allowing the solution to mature and diluting the matured solution by adding water having a TDS of at least 3,000 up to at most 80, 000 ppm.

6. Process according to any one of claims 1 to 5 in which the polymer containing oil recovery formulation has a pH of from 8.5 to 11.

7. Process according any one of claims 1 to 6 in which the alkali is selected from the group consisting of sodium carbonate, ammonium hydroxide and sodium

hydroxide .

8. Process according to any one of claims 1 to 7 in which the formulation further contains surfactant.

9. Process for oil production, which process comprises injecting a polymer containing oil recovery formulation prepared by a process according to any one of claims 1 to

8 into an oil containing formation.

10. The process according to claim 9 wherein water has been injected into the oil containing formation prior to injecting the polymer containing oil recovery

formulation.