WO2020144488A1

WO2020144488A1 - Surfactant composition for enhanced oil recovery

Info

Publication number: WO2020144488A1
Application number: PCT/IB2019/000095
Authority: WO
Inventors: Corinne RICHARD; Jean-Michel GRAS; Valérie MOLINIER; Marcelle SAINT-LOUBERT; Alexandra KLIMENKO; Patrice FORTANE
Original assignee: Total Sa
Priority date: 2019-01-11
Filing date: 2019-01-11
Publication date: 2020-07-16

Abstract

The present invention relates to a surfactant composition, comprising at least one first surfactant compound of formula (I): (I) R¹-O-(CH₂-CH(CH₃)-O)_x-(CH₂-CH₂-O)_y-(CH₂)_w-SO₃ ^-M⁺wherein: R¹ is a linear or branched alkyl radical having from 1 to 24 carbon atoms; x is a number from 2 to 24; y is a number from 0 to 24; w is a number from 0 to 2; and M⁺ is a monovalent cation; and at least one second surfactant compound of formula (II): (II) R²-O-(CH₂CH₂O)_z-H wherein: R² is a linear or branched alkyl radical having from 1 to 18 carbon atoms; and z is a number from 1 to 30. The present invention further relates to a method for extracting hydrocarbons from a subterranean formation.

Description

SURFACTANT COMPOSITION FOR ENHANCED OIL RECOVERY

TECHNICAL FIELD

The present invention relates to the use of a surfactant composition in enhanced oil recovery processes.

TECHNICAL BACKGROUND

Hydrocarbons (such as crude oil) are extracted from a subterranean formation (or reservoir) by means of one or more production wells drilled in the reservoir. Before production begins, the formation, which is a porous medium, is saturated with hydrocarbons.

The initial recovery of hydrocarbons is generally carried out by techniques of“primary recovery", in which only the natural forces present in the reservoir are relied upon. In this primary recovery, only part of the hydrocarbons is ejected from the pores by the pressure of the formation. Typically, once the natural forces are exhausted and primary recovery is completed, there is still a large volume of hydrocarbons left in the reservoir.

This phenomenon has led to the development of enhanced oil recovery (EOR) techniques. Many of such EOR techniques rely on the injection of a fluid into the reservoir in order to produce an additional quantity of hydrocarbons.

The fluid used can in particular be an aqueous solution (“ waterflooding process"), such as brine, which is injected via one or more injection wells.

Large amounts of water can also be recovered from the production wells. This is called“produced watef. The produced water can be e.g. discharged to the environment (after treatment) or reinjected into the subterranean formation via the injection wells.

A polymer can also be added to the water to increase its viscosity and increase its sweep efficiency in recovering hydrocarbons (“ polymer flooding process"). In this case, the produced water contains part of the polymer, which can thus be recovered.

However, in a subterranean formation, droplets of hydrocarbons may be “trapped” in small cavities, therefore surfactants are often used for the mobilization of residual hydrocarbons, as they tend to generate a sufficiently low hydrocarbon/water interfacial tension which makes it possible to overcome capillary forces and allow hydrocarbons to flow. In some cases, the presence of an alkali such as sodium carbonate or a co-solvent such as an alcohol compound is necessary to reduce the risk of gel formation, and to increase reservoir performance. In those cases, these compounds have to be used in large quantities. The presence of an alkali may provoke precipitation of salts and clogging of the injection well. Furthermore, the cost of transporting these compounds on site is not negligible.

Document CA 2 774 318 relates to a process for mineral oil production, in which an aqueous surfactant formulation is forced through the injection wells into a mineral oil deposit, and crude oil is removed from the deposit through the production wells. The surfactant formulation comprises at least one alkyl polyalkoxysulphate containing propoxy groups and also one further, different surfactant.

The article of Zhao P. et al. (Development of high-performance surfactants for difficult oils), 2008 (doi.org/10.2118/113432-MS) relates to internal olefin sulfonate (IOS) surfactants that show excellent performance when tested using crude oils with characteristics such as high wax content and high viscosity.

The article of Barnes J. R. etal. (Controlled hydrophobe branching to match surfactant to crude oil composition for chemical EOR ), 2012 (doi.org/10.2118/154084-MS) relates to an evaluation of several commercially available surfactants (notably IOS surfactants) in tests relevant to both alkaline-surfactant polymer (ASP) and surfactant-polymer (SP) floods, in order to understand how hydrophobe structure is related to surfactant performance and crude oil composition.

The article of Flaaten A. K. et al. (A systematic laboratory approach to low-cost, high-performance chemical flooding), 2008 (doi.org/10.2118/113469-MS) relates to a series of laboratory tests of alternative chemical formulations for a chemical flood design and application. Branched alcohol propoxy sulfates and IOS surfactants showed high performance in these tests.

The article of Tagavifar M. et al. (Measurements of microemulsion viscosity and its implications for chemical enhanced oil recovery), 2017 (doi.org/10.2118/179672-PA) relates to the investigation of the rheological behavior of microemulsion systems with mixtures of oil, brine, surfactant, co-solvent and in some cases polymer, to determine their effects. The article of Levitt D. B. et al. ( Identification and evaluation of high- performance EOR surfactants), 2009, (doi.org/10.21 18/100089-PA) relates to a number of promising EOR surfactants based upon a fast, low-cost laboratory screening process in order to select the best surfactant to use with different crude oils. Branched alcohol propoxy sulfates, IOS surfactants and branched alpha olefin sulfonates have been identified as good EOR surfactants.

There is still a need for a surfactant composition for improving hydrocarbon recovery, in an efficient and cost-effective manner, preferably without using large quantities of chemicals.

SUMMARY OF THE INVENTION

It is a first object of the invention to provide a surfactant composition, comprising:

at least one first surfactant compound of formula (I):

(I) R¹-0-(CH₂-CH(CH3)-0)x-(CH2-CH2-0)y-(CH2)w-S0₃-M⁺ wherein:

R¹ is a linear or branched alkyl radical having from 1 to 24 carbon atoms;

x is a number from 2 to 24;

y is a number from 0 to 24;

w is a number from 0 to 2; and

M⁺ is a monovalent cation; and

at least one second surfactant compound of formula (II):

(I I) R²-0-(CH₂CH₂0)_Z-H

wherein:

R² is a linear or branched alkyl radical having from 1 to 18 carbon atoms; and

z is a number from 1 to 30.

According to some embodiments, R¹ is a linear or branched alkyl radical having from 10 to 20 carbon atoms.

According to some embodiments, x is from 5 to 22.

According to some embodiments, y is from 0 to 10.

According to some embodiments, w is 0.

According to some embodiments, w is 2.

According to some embodiments, M⁺ is selected from Li⁺, Na⁺ and K⁺.

According to some embodiments, R² is a linear or branched alkyl radical having from 8 to 15 carbon atoms.

According to some embodiments, z is from 8 to 15. According to some embodiments, the weight ratio of the first surfactant compound to the second surfactant compound is from 0.1 to 5, preferably from 0.2 to 3, and more preferably from 0.25 to 1 .

According to some embodiments, the composition is an aqueous solution.

According to some embodiments, the aqueous solution comprises an aqueous medium which derives from produced water, fresh water, sea water or aquifer water.

According to some embodiments, the aqueous solution has a salinity from 25 to 150 g/L, and preferably from 30 to 65 g/L.

According to some embodiments, the composition further comprises at least one third surfactant compound of formula (III):

wherein:

R³ and R⁴ are independently chosen from H, or a linear or branched alkyl radical having from 1 to 24 carbon atoms, preferably from 8 to 15 carbon atoms; and

M⁺ is a monovalent cation preferably selected from Li⁺, Na⁺ and K⁺.

According to some embodiments, the third surfactant compound represents from 0.05 to 30% and preferably from 0.1 to 20% by weight of the total amount of surfactants in the composition.

According to some embodiments, the total concentration of surfactant compounds is from 20 to 2000 ppm, and preferably from 30 to 1000 ppm by weight.

According to some embodiments, the composition further comprises a polymer, such as hydrolyzed polyacrylamide, partially hydrolyzed polyacrylamide, poly-N,N-dimethylacrylamide, polyvinyl pyrrolidone, poly(vinylamines), poly(2-acrylamido-2-methyl-1 -propanesulfonic acid), biopolymers such as scleroglucans and xanthan gum, hydrophobically-modified associative polymers, co-polymers of polyacrylamide, 2-acrylamido 2-methylpropane sulfonic acid, and N-vinyl pyrrolidone. According to some embodiments, the composition is substantially devoid of alkali agents such as sodium carbonate, sodium metaborate or sodium hydroxide or ammonia.

According to some embodiments, the composition is substantially devoid of alcohol compounds such as methyl-1 -propanol, 2-butanol, 1 -pentanol, 2-methyl-2-butanol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether or triethylene glycol monobutyl ether.

The invention further relates to a method for extracting hydrocarbons from a subterranean formation, comprising:

providing the surfactant composition described above;

injecting said composition into the subterranean formation; and collecting hydrocarbons displaced by the injected composition.

According to some embodiments, the hydrocarbons of the subterranean formation have a viscosity at 25°C from 18 to 250 cP.

According to some embodiments, the hydrocarbons of the subterranean formation have an API gravity from 20 to 30.

According to some embodiments, the hydrocarbons of the subterranean formation comprise asphaltene compounds and/or naphthenic acid compounds.

According to some embodiments, the composition comprises an aqueous medium and the interfacial tension between the aqueous medium and the hydrocarbons is equal to or less than 0.005 mN/m, preferably equal to or less than 0.003 mN/m, more preferably equal to or less than 0.002 mN/m and most preferably equal to or less than 0.001 mN/m.

According to some embodiments, the injection step(s) are carried out via at least one injection well, and the step(s) of collecting hydrocarbons are carried out via at least one production well.

According to some embodiments, the method for extracting hydrocarbons is a surfactant flooding or a surfactant-polymer flooding or an alkaline-surfactant-polymer flooding process for oil recovery.

According to some embodiments, the injection of the composition into the subterranean formation is carried out in a discontinuous manner.

The invention further relates to a method for selecting the composition described above, comprising the preparation of a plurality of mixtures, each mixture comprising the first surfactant compound of formula (I), the second surfactant compound of formula (II) and optionally the third surfactant compound of formula (III), an aqueous medium and oil, agitating the plurality of mixtures and identifying a mixture which provides a water/oil micro-emulsion. According to some embodiments, the mixtures differ in the nature of at least one of the surfactant compounds; and/or in the concentration of at least one of the surfactant compounds; and/or in the weight ratio of one of the surfactant compounds relative to another one of the surfactant compounds; and/or in the salinity of the aqueous medium.

The present invention makes it possible to address the need mentioned above. In particular the invention provides a surfactant composition for improving hydrocarbon recovery, in an efficient and cost-effective manner, preferably without using large quantities of chemicals.

This is achieved by combining a first surfactant compound with a second surfactant compound. The surfactants as well their amounts and weight ratio can be selected in order to optimize the efficacy of hydrocarbon recovery.

In order to develop an efficient surfactant composition, a widely used method consists in searching for a specific“phase behavio of the mixture comprising hydrocarbons, water and surfactants. Therefore, after mixing these components and after decantation and phase separation, the state of the mixture is observed. According to the desired, specific phase behavior, three separated phases must be observed (one hydrocarbon phase, one aqueous phase and a microemulsion phase). This system is called“Winsor IIG and is characterized in that it is stable over time and does not segregate into an oil phase and a water phase. This makes it possible to achieve an ultra-low interfacial tension between the hydrocarbon phase and the aqueous phase, which is necessary to properly displace the hydrocarbons. Furthermore, Winsor III makes it possible to increase the fluidity of the system which allows transportation of the fluids in a porous medium under satisfactory pressure conditions.

However, this type of microemulsion phase is not easily achieved with certain so-called “difficult’ types of oils (typically viscous and/or heavy hydrocarbons, and/or hydrocarbons comprising heavy compounds such as asphaltenes and naphthenic acid) as they tend to form viscous phases which lead to elevated pressures in the formation.

The surfactant composition of the present invention, and more particularly the combination of a first surfactant compound of formula (I) with a second surfactant compound of formula (II), makes it possible to achieve a Winsor III system even in the case of “difficult’ types of hydrocarbons, and even at a low surfactant concentration.

Therefore, the composition of the present invention allows efficient hydrocarbon recovery without the use of alkalis and co-solvents, which limits the costs and the risk of clogging. Furthermore, as the surfactant composition preferably does not comprise alkali compounds, the composition may be used directly in hard water, without having to soften the water first.

Advantageously, in some cases, the presence of a third surfactant compound of formula (III) may provide even better results, such as a more rapid equilibration of the phases or a more efficient decrease of interfacial tension.

DESCRIPTION OF EMBODIMENTS

The invention will now be described in more detail without limitation in the following description.

Surfactant composition

The invention relies on the use of a surfactant composition comprising at least one first surfactant compound and at least one second surfactant compound which is different from the first surfactant compound.

The first surfactant compound is a compound comprising propoxy groups and optionally ethoxy groups. The first surfactant compound has the formula (I):

(I) R¹-0-(CH₂-CH(CH3)-0)x-(CH2-CH2-0)y-(CH2)w-S0₃-M⁺

R¹ may be an alkyl radical having from 1 to 24 carbon atoms, preferably from 5 to 22, more preferably from 10 to 20 carbon atoms, and even more preferably from 15 to 18 carbon atoms. For example, R¹ may have from 1 to 3 carbon atoms; or from 3 to 6 carbon atoms; or from 6 to 9 carbon atoms; or from 9 to 12 carbon atoms; or from 12 to 15 carbon atoms; or from 15 to 18 carbon atoms; or from 18 to 21 carbon atoms; or from 21 to 24 carbon atoms.

R¹ may be a linear or branched alkyl radical. When R¹ is branched, it may have a mean degree of branching from 0 to 5. More preferably, R¹ is linear.

In formula (I), x may be a number from 2 to 24, and preferably from 5 to 22. For example, x may be from 2 to 4; or from 4 to 6; or from 6 to 8; or from 8 to 10; or from 10 to 12; or from 12 to 14; or from 14 to 16; or from 16 to 18; or from 18 to 20; or from 20 to 22; or from 22 to 24. Number x corresponds to the number of propoxy groups present in the first surfactant compound.

In formula (I), y may be a number from 0 to 24, preferably from 0 to 10, more preferably from 0 to 5; and even more preferably from 0 to 2. For example, y may be from 0 to 0.5; or from 0.5 to 1 ; or from 1 to 2; or from 2 to 4; or from 4 to 6; or from 6 to 8; or from 8 to 10; or from 10 to 12; or from 12 to 14; or from 14 to 16; or from 16 to 18; or from 18 to 20; or from 20 to 22; or from 22 to 24. Number y corresponds to the number of ethoxy groups present in the first surfactant compound. x and y may be integers or not. Namely, if a mixture of different molecules is used, x and/or y correspond to mean degrees of propoxylation and ethoxylation. The mean degree of propoxylation and the mean degree of ethoxylation may be measured by NMR spectroscopy or HPLC/MS.

Preferably, x is higher than y.

The sum x+y may be from 1 to 25 and preferably from 5 to 22.

In formula (I), w represents a number from 0 to 2.

According to some embodiments, the number w may be 0. In this case, the surfactant compound of formula (I) is an alkyl alkoxysulfate surfactant.

According to other embodiments, when the number w is different from 0, it is preferably 2. In this case, the surfactant compound of formula (I) is an alkyl alkoxysulfonate surfactant.

M⁺ is a monovalent cation. M⁺ may be chosen from an alkali metal cation such as Li⁺, Na⁺, K⁺, or an ammonium cation such as NFU⁺. Preferably, M⁺ is chosen from Li⁺, Na⁺, K⁺, and more preferably M⁺ is Na⁺. Therefore, the first surfactant compound may be present as a salt.

The second surfactant compound which is present in the surfactant composition comprises ethoxy groups, and is preferably an alkyl ethoxylate compound. The second surfactant compound has the formula (II):

(I I) R²-0-(CH₂CH₂0)_Z-H

R² may be an alkyl radical having from 1 to 18 carbon atoms, from 5 to 15 carbon atoms, more preferably from 8 to 14 carbon atoms, and even more preferably from 10 to 13 carbon atoms. For example, R² may have from 1 to 3 carbon atoms; or from 3 to 6 carbon atoms; or from 6 to 9 carbon atoms; or from 9 to 12 carbon atoms; or from 12 to 15 carbon atoms; or from 15 to 18 carbon atoms.

R² may be a linear or branched alkyl radical. When R² is branched, it may have a mean degree of branching from 0 to 5.

In formula (II), z may be a number from 1 to 30, preferably from 5 to 25, more preferably from 5 to 15, more preferably from 8 to 14, and even more preferably from 10 to 13. For example, x may be from 1 to 2; or from 2 to 4; or from 4 to 6; or from 6 to 8; or from 8 to 10; or from 10 to 12; or from 12 to 14; or from 14 to 16; or from 16 to 18; or from 18 to 20; or from 20 to 22; or from 22 to 24; or from 24 to 26; or from 26 to 28; or from 28 to 30. Number z corresponds to the number of ethoxy groups present in the second surfactant compound.

Number z may be an integer or not (if it corresponds to a mean degree of ethoxylation). The ratio of the number of carbons present in R² and the number of ethoxy groups (number z) present in the second surfactant compound may be from 0.5 to 2.0, preferably from 0.7 to 1 .

The surfactant composition may further comprise at least one third surfactant compound of formula (III):

(III)

R³ and R⁴ may be independently chosen from a hydrogen atom, or an alkyl radical having from 1 to 24 carbon atoms, preferably from 5 to 15 and more preferably from 8 to 13 carbon atoms. For example, R³ and R⁴ may independently have from 1 to 3 carbon atoms; or from 3 to 6 carbon atoms; or from 6 to 9 carbon atoms; or from 9 to 12 carbon atoms; or from 12 to 15 carbon atoms; or from 15 to 18 carbon atoms; or from 18 to 21 carbon atoms; or from 21 to 24 carbon atoms. R³ and R⁴ may be linear or branched alkyl radicals.

According to some embodiments, R³ and R⁴ are different.

According to other embodiments, R³ and R⁴ are the same.

R³ may be in the ortho position relative to S03 M⁺, or in the meta position relative to S03 M⁺, or in the para position relative to S03 M⁺.

R⁴ may be in the ortho position relative to S03 M⁺, or in the meta position relative to S03 M⁺, or in the para position relative to S03 M⁺.

R³ and R⁴ may have an ortho relative configuration, or a meta relative configuration, or a para relative configuration.

M⁺ is a monovalent cation. M⁺ may be chosen from an alkali metal cation such as Li⁺, Na⁺, K⁺, or an ammonium cation such as NhV. Preferably, M⁺ is chosen from Li⁺, Na⁺, K⁺, and more preferably M⁺ is Na⁺. Therefore, the third surfactant compound may be present as a salt.

The weight ratio of the first surfactant compound to the second surfactant compound in the surfactant composition may be from 0.1 to 5, preferably from 0.2 to 3, and more preferably from 0.25 to 1 . For example, this ratio may be from 0.1 to 0.2; or from 0.2 to 0.4; or from 0.4 to 0.6; or from 0.6 to 0.8; or from 0.8 to 1 ; or from 1 .2 to 1 .4; or from 1 .4 to 1 .6; or from 1 .6 to 1 .8; or from 1 .8 to 2; or from 2 to 2.5; or from 2.5 to 3; or from 3 to 3.5; or from 3.5 to 4; or from 4 to 4.5; or from 4.5 to 5. When the third surfactant compound is present in the surfactant composition, it may represent from 0.05 to 30%, and preferably from 0.1 to 20% by weight of the total amount of surfactants in the composition. Therefore, the third surfactant compound may represent from 0.05 to 0.1 %; or from 0.1 to 1 %; or from 1 to 5%; or from 5 to 10%; or from 10 to 15%; or from 15 to 20%; or from 20 to 25%; or from 25 to 30% by weight of the total amount of surfactants in the composition.

The surfactant composition may also comprise one or more polymers. The polymer may be chosen from hydrolyzed polyacrylamide, partially hydrolyzed polyacrylamide, poly-N,N-dimethylacrylamide, polyvinyl pyrrolidone, poly(vinylamines), poly(2-acrylamido-2-methyl-1 -propanesulfonic acid), biopolymers such as scleroglucans and xanthan gum, hydrophobically-modified associative polymers, co-polymers of polyacrylamide, 2-acrylamido 2-methylpropane sulfonic acid, and N-vinyl pyrrolidone

The surfactant composition may also comprise one or more additives. Such additives may include additional surfactants (not according to formula (I), (II) or (III)), salts, sacrificial agents, mobility control polymers, pH adjustment agents, solvents and mixtures thereof.

The surfactant composition according to the invention is preferably an aqueous solution. Therefore, the surfactant composition may comprise an aqueous medium wherein the surfactant compounds are dissolved. The aqueous medium may derive from produced water, fresh water, sea water or aquifer water.

According to some embodiments, the aqueous solution may have a salinity from 25 to 150 g/L, and preferably from 30 to 65 g/L. For example, the aqueous solution may have a salinity from 25 to 30 g/L; or from 30 to 35 g/L; or from 35 to 40 g/L; or from 40 to 45 g/L; or from 45 to 50 g/L; or from 50 to 55 g/L; or from 55 to 60 g/L; or from 60 to 65 g/L; or from 65 to 70 g/L; or from 70 to 75 g/L; or from 75 to 80 g/L; or from 80 to 85 g/L; or from 85 to 90 g/L; or from 90 to 95 g/L; or from 95 to 100 g/L; or from 100 to 105 g/L; or from 105 to 1 10 g/L; or from 1 10 to 1 15 g/L; or from 1 15 to 120 g/L; or from 120 to 125 g/L; or from 125 to 130 g/L; or from 130 to 135 g/L; or from 135 to 140 g/L; or from 140 to 145 g/L; or from 145 to 150 g/L. Salinity is defined herein as the total concentration of dissolved inorganic salts in water, including e.g. NaCI, CaCh, MgCh and any other inorganic salts.

According to some embodiments, the aqueous solution may comprise ions such as calcium and/or magnesium, mostly in the form of bicarbonates, sulfates and chlorides. Therefore, the aqueous solution may comprise equal to or more than 60 ppm by weight of Ca²⁺, preferably equal to or more than 80 ppm by weight of Ca²⁺, more preferably equal to or more than 100 ppm by weight of Ca²⁺, more preferably equal to or more than 120 ppm by weight of Ca²⁺, more preferably equal to or more than 140 ppm by weight of Ca²⁺, more preferably equal to or more than 180 ppm by weight of Ca²⁺, more preferably equal to or more than 200 ppm by weight of Ca²⁺, more preferably equal to or more than 250 ppm by weight of Ca²⁺, more preferably equal to or more than 500 ppm by weight of Ca²⁺, and even more preferably equal to or more than 1000 ppm by weight of Ca²⁺.

Furthermore, the aqueous solution may comprise equal to or more than 60 ppm by weight of Mg²⁺, preferably equal to or more than 80 ppm by weight of Mg²⁺, more preferably equal to or more than 100 ppm by weight of Mg²⁺, more preferably equal to or more than 120 ppm by weight of Mg²⁺, more preferably equal to or more than 140 ppm by weight of Mg²⁺, more preferably equal to or more than 180 ppm by weight of Mg²⁺, more preferably equal to or more than 200 ppm by weight of Mg²⁺, more preferably equal to or more than 300 ppm by weight of Mg²⁺,and even more preferably equal to or more than 400 ppm by weight of Mg²⁺.

The surfactant composition according to the invention may comprise a total concentration of surfactant compounds (first surfactant compounds, second surfactant compounds and optionally third surfactant compounds and additional surfactant compounds) from 20 to 2000 ppm; and preferably from 30 to 1000 ppm. The concentration of surfactant compounds may be for example from 30 to 40 ppm; or from 40 to 50 ppm, or from 50 to 100 ppm; or from 100 to 200 ppm; or from 200 to 300 ppm; or from 300 to 400 ppm; or from 400 to 500 ppm; or from 500 to 600 ppm; or from 600 to 700 ppm; or from 700 to 800 ppm; or from 800 to 900 ppm; or from 900 to 1000 ppm; or from 1000 to 1 100 ppm; or from 1 100 to 1200 ppm; or from 1200 to 1300 ppm; or from 1300 to 1400 ppm; or from 1400 to 1500 ppm; or from 1500 to 1600 ppm; or from 1600 to 1700 ppm; or from 1700 to 1800 ppm; or from 1800 to 1900 ppm; or from 1900 to 2000 ppm. These concentrations especially apply if the surfactant composition is in the form of an aqueous solution.

The surfactant composition according to the invention may be substantially devoid of, preferably devoid of, sodium carbonate.

The surfactant composition according to the invention may be substantially devoid of, preferably devoid of, sodium metaborate.

The surfactant composition according to the invention may be substantially devoid of, preferably devoid of, sodium hydroxide. The surfactant composition according to the invention may be substantially devoid of, preferably devoid of, any alkali agents, including sodium carbonate, sodium metaborate or sodium hydroxide or ammonia.

The surfactant composition according to the invention may be substantially devoid of, preferably devoid of, one or more, preferably all, of methyl-1 -propanol (/so-butanol), 2-butanol (sec-butanol), 1 -pentanol, 2-methyl-2-butanol (f-pentanol), ethylene glycol monobutyl ether (EGBE), diethylene glycol monobutyl ether (DGBE) or triethylene glycol monobutyl ether (TGBE).

The surfactant composition according to the invention may be substantially devoid of, preferably devoid of, any alcohol compound.

The surfactant composition according to the invention may be substantially devoid of, preferably devoid of, any co-solvent, including alcohol compounds.

Method for extracting hydrocarbons

The present invention further relates to a method for extracting hydrocarbons from a subterranean formation. The subterranean formation may in particular be a carbonated reservoir. The method may comprise the following steps:

providing the surfactant composition as described above; injecting said composition into the subterranean formation; and collecting hydrocarbons displaced by the injected surfactant composition.

Preferably, the surfactant composition is provided as an aqueous solution.

Alternatively, if the surfactant composition is initially provided for example in a solid form, the method may further comprise a step of mixing the surfactant composition with an aqueous medium to form an aqueous solution, prior to the injection of the surfactant composition in the form of this aqueous solution. The aqueous medium used to form the aqueous solution may be or may derive from produced water, fresh water, sea water or aquifer water.

According to some embodiments, the method according to the invention may be a surfactant flooding process.

According to other embodiments, when one or more polymers are present in the surfactant composition, the method according to the invention may be a surfactant-polymer flooding process.

The temperature in the subterranean formation may range from 25 to 140°C, preferably from 40 to 140°C and more preferably from 50 to 120°C. For example, if the temperature is relatively low, such as for instance not more than 70°C, first surfactant compound comprising a sulfate group may be used. Otherwise, it may be preferred to use a first surfactant compound comprising a sulfonate group.

The injection of the surfactant composition may be performed at a pressure of from 70 to 300 bar, preferably from 100 to 250 bar.

The hydrocarbons in the subterranean formation may preferably have a viscosity at 25°C from 5 to 250 cP, preferably from 18 to 250 cP, and more preferably from 50 to 240 cP. For example, this viscosity may be from 5 to 10 cP; or from 10 to 25 cP; or from 25 to 50 cP; or from 50 to 100 cP; or from 100 to 150 cP; or from 150 to 200 cP; or from 200 to 250 cP. The viscosity is measured with a Stabinger densimeter/viscometer.

Furthermore, prior to the injection, the hydrocarbons from the subterranean formation may preferably have an API gravity from 20 to 30. For example, the hydrocarbons may have an API gravity from 20 to 22; or from 22 to 24; or from 24 to 26; or from 26 to 28; or from 28 to 30. The“API gravity" (American Petroleum Institute gravity) is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if its API gravity is less than 10, it is heavier and sinks in water.

The hydrocarbons of the subterranean formation may comprise asphaltene compounds and/or naphthenic acid compounds.

The interfacial tension between the water of the aqueous surfactant composition and the hydrocarbons may be equal to or less than 0.005 mN/m, preferably equal to or less than 0.003 mN/m, more preferably equal to or less than 0.002 mN/m and most preferably equal to or less than 0.001 mN/m. The interfacial tension may be measured using a spinning drop tensiometer. Alternatively, the interfacial tension may be calculated from the value of the solubilization ratio measured during a phase behavior experiment using the Chun Fluh equation.

The method according to the invention, therefore, makes it possible to minimize the interfacial tension between water and hydrocarbons in order to mobilize the hydrocarbons trapped in the subterranean formation and increase oil production. In fact, as the interfacial tension between water and hydrocarbons is decreased and as droplets of hydrocarbons are forced out of the cavities, the droplets tend to combine and form a continuous layer. Therefore, as this layer advances through the subterranean formation, more droplets can coalesce with the layer. Furthermore, as the droplets combine to form the layer, the water- hydrocarbon interface is reduced, the surfactant compounds are no longer required and are therefore released to mobilize other remaining droplets in the subterranean formation. The injection of the surfactant composition is carried out via one or more injection wells.

The collection of hydrocarbons is carried out via one or more production wells.

According to some embodiments, at least part of the surfactant compounds may be recovered with the collected hydrocarbons and water. Alternatively, only hydrocarbons are collected while the surfactant compounds remain in the subterranean formation.

The injection of the composition into the subterranean formation may preferably be implemented in a continuous manner, i.e. the surfactant composition is continuously injected into the subterranean formation, for a period of time of at least 1 day, or at least 1 week, or at least 1 month, or at least 2 months, or at least 3 months, or at least 4 months, or at least 6 months, or at least 1 year.

Determination of the nature and properties of surfactants

In a preferred variation, the nature and/or the proportions of the first surfactant compound and the second surfactant compound and optionally the third surfactant compound are selected in a selection method implemented before actually injecting the surfactant composition into the subterranean formation, as described above. This preliminary selection method makes it possible to optimize the efficacy of the surfactant composition depending on the characteristics of the subterranean formation and more particularly depending on the characteristics of the hydrocarbons present in the subterranean formation.

To this end, several mixtures are prepared.

Each mixture comprises a portion of an aqueous medium (such as produced water for example or another aqueous medium having the same properties as the water that will be injected in the subterranean formation, and in particular having the same salinity), a proportion of hydrocarbons (such as oil recovered from the subterranean formation or oil having similar properties to the oil recovered from the subterranean formation), and a portion of the surfactant composition which is to be tested.

For example, for a given surfactant compound of formula (II), the different mixtures may comprise the surfactant compound of formula (II) and surfactant compounds of formula (I) with different numbers of propoxy groups (number x) and/or different numbers of ethoxy groups (number y).

Furthermore, for a given surfactant compound of formula (II), the different mixtures may comprise the surfactant compound of formula (II) and surfactant compounds of formula (I) with different numbers w (sulfate or sulfonate surfactants).

For a given surfactant compound of formula (I), the different mixtures may comprise the surfactant compound of formula (I) and surfactant compounds of formula (II) with different ratios of the number of carbons present in R² and the number of ethoxy groups (number z) present in the surfactant compound of formula (II).

For a given surfactant compound of formula (I) and a given surfactant compound of formula (II) the different mixtures may include different relative proportions of the two surfactants.

For a given surfactant compound of formula (I) and a given surfactant compound of formula (II) the different mixtures may include the presence of the surfactant compound of formula (III) in different concentrations.

Each mixture is agitated for example in a vial or other container, and the visual aspect of the various mixtures is compared. Each mixture is left standing until equilibrium between the different phases is established. When an equilibrium is obtained, the mixtures are classified into three types of systems.

In some of the mixtures, droplets of oil may be dispersed in a water phase (“ oil-in-water emulsion" or “Winsor G). In others, droplets of water may be dispersed in an oil phase (“ water-in-oil emulsion" or“Winsor II"). In yet others, a “Winsor III" system may be obtained, with an oil/water micro-emulsion containing approximately as much water as oil.

Once one or more mixtures in which such a micro-emulsion is present have been identified, the nature and/or proportions of the surfactants for the implementation of the invention are selected according to this mixture or to one of these mixtures.

The present selection method may be preferably performed at the average temperature of bottom of the injection well.

EXAMPLES

The following examples illustrate the invention without limiting it.

Example 1

In this example, the experiment was conducted within 5 mL-glass pipettes sealed at the bottom, at 55°C in order to simulate the temperature of the subterranean formation. The oil used for this experiment is reconstituted oil having a density of 0.8816 g/cm³ at 55°C and a viscosity of 6.5 cP at 55°C.

The surfactant composition used comprises a first surfactant compound of formula (I): Ci6-i8-0-(CH₂-CH(CH3)-0)₇-(CH₂-CH₂-0)o_.i-SC>3Na, wherein the C16-18 group is linear, at a concentration of 0.25% by weight; and a second surfactant compound of formula (II): CIO-0-(CH2CH20)IO-H, wherein the C10 group is branched, at a concentration of 0.5% by weight.

Different samples were prepared each comprising oil, the surfactant composition and an aqueous medium, with different salinities varying from 30 to 100 g/L. The samples had a WOR (Water-Oil Ratio) of 3, therefore 3 ml_ of salted water containing the surfactants and then 1 ml_ of oil were poured into the pipette. 15 pipettes were prepared, at different salinities. The salinity was adjusted by mixing seawater (salinity 25.5 g/L) and formation water (salinity 1 15.5 g/L) in various ratios.

The pipettes were then sealed under a nitrogen flow and placed at the desired temperature (55°C) for 10 minutes. They were then gently mixed and then mixed again after 1 hour, 2 hours and one night of equilibration.

Observations of phase behavior were made after complete stabilization (several days to several weeks).

The visual inspection of the contents of the tube revealed that, for those samples having salinities of 50 g/L, 55 g/L, and 60 g/L, a Winsor III system was obtained, and that an interfacial tension of approximately 0.002 mN/m was reached without the use of an alkali. No viscous phase was observed over the range of salinity from 50 to 100 g/L.

Example 2

The surfactant composition of example 1 was used for oil recovery in a core simulating a subterranean formation (of the sand or carbonate type) at low concentrations as illustrated in the Table below. The oil is the same as the one used in example 1 . Therefore, the core was firstly filled with synthetic formation brine which was then displaced by the oil until no more water was produced. Then, synthetic injected brine was injected until no more oil was produced followed by the injection of surfactant-polymer formulation. All experiments were performed at reservoir temperature but ambient pressure.

A= Ci6-i8-0-(CH₂-CH(CH3)-0)₇-(CH₂-CH₂-0)o_.i-S0₃Na

B= CIO-0-(CH₂CH₂0)IO-H

By“saturation in residual oil after injection of the surfactant composition’’ is meant the ratio of volume of oil remaining in the porous medium after injection of the surfactant composition to total pore volume.

By“saturation in remaining oif’ is meant a ratio of volume of oil remaining in the porous medium after injection of synthetic injected brine, therefore before the injection of the surfactant formulation, to total pore volume.

As illustrated in the table above, the surfactant composition makes it possible to achieve an efficient oil recovery even in low concentrations of surfactant composition for carbonate as well as for sand porous medium.

Example 3

In this example, the experiment was conducted within 5 mL-glass pipettes sealed at the bottom, at 65°C in order to simulate the temperature of the subterranean formation. The oil used for this experiment is a dead oil having a density of 0.9060 g/cm³ at 65°C and a viscosity of 33.56 cP at 65°C.

The surfactant composition used comprises a first surfactant compound of formula (I): Ci6-i8-0-(CH₂-CH(CH3)-0)₂₂-SC>3Na, wherein the C16-18 is linear, at a concentration of 0.5% by weight; and a second surfactant compound of formula (II): CIO-0-(CH2CH20)IO-H, wherein the C10 group is branched, at a concentration of 0.6% by weight.

Different samples were prepared each comprising oil, the surfactant composition and an aqueous medium, with different salinities varying from 30 to 60 g/L. The samples had a WOR of 3, therefore 3 ml_ of salted water containing the surfactants and then 1 ml_ of oil were poured into the pipette. 7 pipettes were prepared, at different salinities. The salinity was adjusted by mixing desulfated water (salinity 27.5 g/L) and formation water (salinity 61 .9 g/L) in various ratios.

The pipettes were then sealed under a nitrogen flow and placed at the desired temperature (65°C) for 10 minutes. They were then gently mixed and then mixed again after 1 hour, 2 hours and one night of equilibration.

The visual inspection of the contents of the tube revealed that, for those samples having salinities of 35 g/L and 40 g/L, a Winsor III system was obtained and that an interfacial tension of approximately 0.003 mN/m was reached without the use of an alkali. The decantation of the system was slower than in case of the oil of example 1 , but no viscous phase was observed over the range of salinity from 30 to 60 g/L.

Example 4

In this example, the surfactant composition of example 3 was replaced by a surfactant composition comprising a first surfactant compound of formula (I): Ci6-i8-0-(CH₂-CH(CH3)-0)₂₂-SC>3Na, wherein the C16-18 group is linear, at a concentration of 0.4% by weight; a second surfactant compound of formula (II): CIO-0-(CH2CH20)IO-H, wherein the C10 group is branched, at a concentration of 0.4% by weight and a third surfactant compound of formula (III) at a concentration of 0.1 %. (III):

The visual inspection of the contents of the tube revealed that, for those samples having salinities of 30 g/L and 35 g/L, a Winsor III system was obtained and that an interfacial tension of approximately 0.004 mN/m was reached without the use of an alkali. The phase separation was faster than in the case of the surfactant composition of example 3. No viscous phase was observed over the range of salinity from 30 to 60 g/L.

Example 5

In this example, the surfactant composition of example 4 was replaced by a surfactant composition comprising a first surfactant compound of formula (I): Ci6-i8-0-(CH₂-CH(CH3)-0)₇-(CH₂-CH₂-0)o_.i-SC>3Na, wherein the C16-18 group is linear, at a concentration of 0.35% by weight; a second surfactant compound of formula (II): Ci3-0-(CH₂CH₂0)i3-H, wherein the C10 group is branched, at a concentration of 0.325% by weight and a third surfactant compound of formula (III) at a concentration of 0.15%.

(III):

Different samples were prepared each comprising oil, the surfactant composition and an aqueous medium, with different salinities of 30 g/L and 60 g/L.

The samples had a WOR of 3, therefore 3 ml_ of salted water containing the surfactants and then 1 ml_ of oil were poured into the pipette. 7 pipettes were prepared, at different salinities. The salinity was adjusted by mixing desulfated water (salinity 27.5 g/L) and formation water (salinity 61.9 g/L) in various ratios.

Observations of phase behavior were made after complete stabilization

(several days to several weeks).

The visual inspection of the contents of the tube revealed that, for the sample having a salinity of 40 g/L, a Winsor III system was obtained, and no viscous phase was observed.

Claims

1. A surfactant composition, comprising:

at least one first surfactant compound of formula (I):

(I) R¹-0-(CH₂-CH(CH3)-0)x-(CH2-CH2-0)y-(CH2)w-S0₃-M⁺ wherein:

R¹ is a linear or branched alkyl radical having from 1 to 24 carbon atoms;

x is a number from 2 to 24;

y is a number from 0 to 24;

w is a number from 0 to 2; and

M⁺ is a monovalent cation; and

at least one second surfactant compound of formula (II):

(II) R²-0-(CH₂CH₂0)_Z-H

wherein:

R² is a linear or branched alkyl radical having from 1 to 18 carbon atoms; and

z is a number from 1 to 30.

2. The composition according to claim 1 , wherein R¹ is a linear or branched alkyl radical having from 10 to 20 carbon atoms.

3. The composition according to any one of claims 1 or 2, wherein x is from 5 to 22.

4. The composition according to any one of claims 1 to 3, wherein y is from 0 to 10.

5. The composition according to any one of claims 1 to 4, wherein w is 0.

6. The composition according to any one of claims 1 to 5, wherein w is 2.

7. The composition according to any one of claims 1 to 6, wherein M⁺ is selected from Li⁺, Na⁺ and K⁺.

8. The composition according to any one of claims 1 to 7, wherein R² is a linear or branched alkyl radical having from 8 to 15 carbon atoms.

9. The composition according to any one of claims 1 to 8, wherein z is from 8 to 15.

10. The composition according to any one of claims 1 to 9, wherein the weight ratio of the first surfactant compound to the second surfactant compound is from 0.1 to 5, preferably from 0.2 to 3, and more preferably from 0.25 to 1 .

11. The composition according to any one of claims 1 to 10, which is an aqueous solution.

12. The composition according to claim 1 1 , wherein the aqueous solution comprises an aqueous medium which derives from produced water, fresh water, sea water or aquifer water.

13. The composition according to claim 1 1 or 12, wherein the aqueous solution has a salinity from 25 to 150 g/L, and preferably from 30 to 65 g/L.

14. The composition according to any one of claims 1 to 13, further comprising at least one third surfactant compound of formula (III):

(III)

wherein:

M⁺ is a monovalent cation preferably selected from Li⁺, Na⁺ and

K⁺

15. The composition according to claim 14, wherein the third surfactant compound represents from 0.05 to 30% and preferably from 0.1 to 20% by weight of the total amount of surfactants in the composition.

16. The composition according to any one of claims 1 to 15, wherein the total concentration of surfactant compounds is from 20 to 2000 ppm, and preferably from 30 to 1000 ppm by weight.

17. The composition according to any one of claims 1 to 16, further comprising a polymer, such as hydrolyzed polyacrylamide, partially hydrolyzed polyacrylamide, poly-N,N-dimethylacrylamide, polyvinyl pyrrolidone, poly(vinylamines), poly(2-acrylamido-2-methyl-1- propanesulfonic acid), biopolymers such as scleroglucans and xanthan gum, hydrophobically-modified associative polymers, co polymers of polyacrylamide, 2-acrylamido 2-methylpropane sulfonic acid, and N-vinyl pyrrolidone.

18. The composition according to any one of claims 1 to 17, which is substantially devoid of alkali agents such as sodium carbonate, sodium metaborate or sodium hydroxide or ammonia.

19. The composition according to any one of claims 1 to 18, which is substantially devoid of alcohol compounds such as methyl-1 - propanol, 2-butanol, 1-pentanol, 2-methyl-2-butanol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether or triethylene glycol monobutyl ether.

20. A method for extracting hydrocarbons from a subterranean formation, comprising:

providing the surfactant composition according to any one of claims 1 to 19;

21. The method according to claim 20, wherein the hydrocarbons of the subterranean formation have a viscosity at 25°C from 18 to 250 cP.

22. The method according to any one of claims 20 or 21 , wherein, the hydrocarbons of the subterranean formation have an API gravity from 20 to 30.

23. The method according to any one of claims 20 to 22, wherein the hydrocarbons of the subterranean formation comprise asphaltene compounds and/or naphthenic acid compounds.

24. The method according to any one of claims 20 to 23, wherein the composition comprises an aqueous medium and the interfacial tension between the aqueous medium and the hydrocarbons is equal to or less than 0.005 mN/m, preferably equal to or less than 0.003 mN/m, more preferably equal to or less than 0.002 mN/m and most preferably equal to or less than 0.001 mN/m.

25. The method according to any one of claims 20 to 24, wherein the injection step(s) are carried out via at least one injection well, and the step(s) of collecting hydrocarbons are carried out via at least one production well.

26. The method according to any one of claims 20 to 25, which is a surfactant flooding or a surfactant-polymer flooding or an alkaline- surfactant-polymer flooding process for oil recovery.

27. The method according to any one of claims 20 to 26, wherein the injection of the composition into the subterranean formation is carried out in a discontinuous manner.

28. A method for selecting the composition according to any one of claims 1 to 19, comprising the preparation of a plurality of mixtures, each mixture comprising the first surfactant compound of formula (I), the second surfactant compound of formula (II) and optionally the third surfactant compound of formula (III), an aqueous medium and oil, agitating the plurality of mixtures and identifying a mixture which provides a water/oil micro-emulsion.

29. The method of claim 28, wherein the mixtures differ in the nature of at least one of the surfactant compounds; and/or in the concentration of at least one of the surfactant compounds; and/or in the weight ratio of one of the surfactant compounds relative to another one of the surfactant compounds; and/or in the salinity of the aqueous medium.