WO2019113049A1

WO2019113049A1 - A method of producing an alcohol propoxy sulfate

Info

Publication number: WO2019113049A1
Application number: PCT/US2018/063821
Authority: WO
Inventors: Lori Ann Crom; Sonja Geib; Julian Richard Barnes; Carmen Geraldine REZNIK; Michael Joseph Doll; David Perez REGALADO
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2017-12-05
Filing date: 2018-12-04
Publication date: 2019-06-13
Also published as: AR114937A1; UY37992A

Abstract

A method of producing alcohol propoxy sulfates comprising sulfating an alcohol propoxylate by contacting the alcohol propoxylate with a sulfating agent under sulfation conditions wherein the sulfation conditions comprise feeding the sulfating agent at a molar ratio of SO₃ to alcohol propoxylate of at least 1.14:1 and a composition produced thereby comprising alcohol propoxy sulfates, unreacted alcohol propoxylates (UOM), and polypropoxy disulfate (PDS) wherein the concentration of UOM is less than 10 wt% and the concentration of PDS is greater than 5 wt%. The composition may be used for treating a hydrocarbon containing formation.

Description

A METHOD OF PRODUCING AN ALCOHOL PROPOXY SULFATE

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U. S. Provisional Patent Application Serial No. 62/594,649, filed December 5, 2017.

FIELD OF THE INVENTION

[0002] The invention relates to an alcohol propoxy sulfate composition, a method of producing that composition and a use of that composition.

BACKGROUND OF THE INVENTION

[0003] Hydrocarbons may be recovered from hydrocarbon containing formations (or reservoirs) by penetrating the formation with one or more wells, which may allow the hydrocarbons to flow to the surface. A hydrocarbon containing formation may have one or more natural components that may aid in mobilizing hydrocarbons to the surface of the wells. For example, gas may be present in the formation at sufficient levels to exert pressure on the hydrocarbons to mobilize them to the surface of the production wells. These are examples of so- called“primary oil recovery”.

[0004] However, reservoir conditions (for example permeability, hydrocarbon concentration, porosity, temperature, pressure, composition of the rock, concentration of divalent cations (or hardness), etc.) can significantly impact the economic viability of hydrocarbon production from any particular hydrocarbon containing formation.

[0005] Furthermore, the above-mentioned natural pressure-providing components may become depleted over time, often long before the majority of hydrocarbons have been extracted from the reservoir. Therefore, supplemental recovery processes may be required and used to continue the recovery of hydrocarbons from the hydrocarbon containing formation. This supplemental oil recovery is often called“secondary oil recovery” or“tertiary oil recovery”. Examples of known supplemental processes include waterflooding, polymer flooding, gas flooding, alkali flooding, thermal processes, solution flooding, solvent flooding, or combinations thereof. Various surfactants may be used in these supplemental processes, but some surfactants are less effective under certain reservoir conditions. For example, alcohol alkoxy sulfates (AAS) may have a less than desirable aqueous solubility in certain brines. SUMMARY OF THE INVENTION

[0006] The invention provides a method of producing alcohol propoxy sulfates comprising sulfating an alcohol propoxylate by contacting the alcohol propoxylate with a sulfating agent under sulfation conditions wherein the sulfation conditions comprise feeding the sulfating agent at a molar ratio of SO3 to alcohol propoxylate of at least 1.14: 1.

[0007] The invention provides a composition comprising alcohol propoxy sulfates, unreacted alcohol propoxylates (UOM), and polypropoxy disulfate (PDS) wherein the concentration of UOM is less than 10 wt% and the concentration of PDS is greater than 5 wt%.

[0008] The invention provides a method of treating a hydrocarbon containing formation comprising providing a hydrocarbon recovery composition to at least a portion of the hydrocarbon containing formation and allowing the hydrocarbon recovery composition to contact the formation wherein the hydrocarbon recovery composition comprises alcohol propoxy sulfates, alcohol propoxylates, and polypropoxy disulfate wherein the weight ratio of polypropoxy disulfate to alcohol propoxy sulfates is at least 1:20 and the weight ratio of alcohol propoxylates to alcohol propoxy sulfates is less than 1: 10.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The invention provides a method of producing an alcohol propoxy sulfate that has an improved aqueous solubility which makes it more suitable for use as a surfactant in a hydrocarbon recovery composition. The alcohol propoxy sulfate is a compound of the formula (I)

Formula (I) R-0-[PO]_x-X

wherein R is a hydrocarbyl group, PO is a propylene oxide group, x is the number of propylene oxide groups; and X is a group comprising a sulfate moiety. The alcohol propoxy sulfate may be formed by propoxylating an alcohol, and then sulfating the resulting alcohol propoxylate, and these steps will be described in more detail hereinafter.

Alcohol and Method of Making

[0010] The R group in the starting alcohol R-OH is the same R group as in the resulting alcohol propoxy sulfate. The R group is preferably aliphatic, and it may be an alkyl group, cycloalkyl group or alkenyl group. The R group is preferably an alkyl group. The R group may be substituted by another hydrocarbyl group or by a substituent which contains one or more heteroatoms, for example a hydroxy group or an alkoxy group.

[0011] The alcohol may be an alcohol containing 1 hydroxyl group (mono-alcohol) or an alcohol containing from 2 to 6 hydroxyl groups (poly-alcohol). Suitable examples of poly-alcohols are diethylene glycol, dipropylene glycol, glycerol, pentaerythritol, trimethylolpropane, sorbitol and mannitol. The alcohol is preferably a mono-alcohol. Further, the alcohol may be a primary or secondary alcohol, preferably a primary alcohol.

[0012] The alcohol may comprise a range of different molecules which may differ from one another in terms of carbon number for the R group, the R group being branched or unbranched, the number of branches for the R group, and the molecular weight. Generally, the R group may be a branched hydrocarbyl group or an unbranched (linear) hydrocarbyl group.

[0013] The R group has a weight average carbon number within a wide range, namely 5 to 32, preferably 6 to 25, more preferably 7 to 22, most preferably 8 to 20. In another embodiment, the weight average carbon number is 9 to 17. In a case where the alkyl group contains 3 or more carbon atoms, the alkyl group is attached either via its terminal carbon atom or an internal carbon atom to the oxygen atom, preferably via its terminal carbon atom. Further, the weight average carbon number of the alkyl group is at least 5, preferably at least 6, more preferably at least 7, more preferably at least 8, more preferably at least 9, more preferably at least 10, more preferably at least 11 , most preferably at least 12. Still further, the weight average carbon number of the alkyl group is at most 32, preferably at most 25, more preferably at most 20, more preferably at most 17, more preferably at most 16, more preferably at most 15, more preferably at most 14, most preferably at most 13. The weight average carbon number may be in a range of from 9 to 13.

[0014] In one embodiment, the R group is preferably a largely branched alkyl group which has a branching index equal to or greater than 0.15. The branching index is determined by dividing the total number of branches by the total number of molecules. The branching index can be determined by ¹ H-NMR analysis. The branching index of the R group is preferably of from 0.3 to 3.0, most preferably 1.2 to 1.4. Further, the branching index is at least 0.3, preferably at least 0.5, more preferably at least 0.7, more preferably at least 0.9, more preferably at least 1.0, more preferably at least 1.1, most preferably at least 1.2. Still further, the branching index is preferably at most 3.0, more preferably at most 2.5, more preferably at most 2.2, more preferably at most 2.0, more preferably at most 1.8, more preferably at most 1.6, most preferably at most 1.4.

[0015] In another embodiment, the R group is preferably a largely linear alkyl group which has a branching index of about 0.2. Alcohols having largely linear R groups may be alcohols based on the modified OXO hydroformylation process where an olefin is converted to an alcohol.

[0016] The alcohol may be prepared in any way. For example, a primary aliphatic alcohol may be prepared by hydroformylation of a branched olefin. Preparations of branched olefins are described in US 5,510,306; US 5,648,584 and US 5,648,585. Preparations of branched long chain aliphatic alcohols are described in US 5,849,960; US 6,150,222; US 6,222,077. In another embodiment, the alcohols may be obtained by the Ziegler process.

[0017] Alcohols as described above are commercially available. A suitable example of a commercially available alcohol mixture is NEODOL™ 67, which includes a mixture of Ci₆ and Cn alcohols of the formula R-OH, wherein R is a branched alkyl group having a branching index of about 1.3, sold by Shell Chemical LP. NEODOL™ as used throughout this text is a trademark. Shell Chemical LP also manufactures a C12/C13 analogue alcohol of NEODOL™ 67, which includes a mixture of C12 and C13 alcohols of the formula R-OH, wherein R is a branched alkyl group having a branching index of about 1.3. Other suitable examples from Shell Chemical LP include NEODOL™ 91 and NEODOL™ 23 wherein R is a branched alkyl group having a branching index of about 0.2. Another suitable example is EXXAL™ 13 tridecylalcohol (TDA), sold by ExxonMobil, which is of the formula R-OH wherein R is a branched alkyl group having a branching index of about 2.9 and having a carbon number distribution wherein 30 wt.% is C12, 65 wt.% is C13 and 5 wt.% is Ci₄. Yet another suitable example is MARLIPAL® tridecylalcohol (TDA), sold by Sasol, which is of the formula R-OH wherein R is a branched alkyl group having a branching index of about 2.2 and having 13 carbon atoms.

Propoxylate and Method of Making

[0018] The alcohol described above is propoxylated to produce an alcohol propoxylate, R-O- [PO]_x-H, by reacting with propylene oxide in the presence of an appropriate alkoxylation catalyst. The alkoxylation catalyst may be potassium hydroxide or sodium hydroxide which are commonly used commercially. Alternatively, a double metal cyanide catalyst may be used, as described in US 6,977,236. Still further, a lanthanum-based or a rare-earth metal-based alkoxylation catalyst may be used, as described in US 5,059,719 and US 5,057,627. The alkoxylation reaction temperature may range from 90 °C to 250 °C, preferably from 120 to 220 °C, and super atmospheric pressures may be used if it is desired to maintain the alcohol substantially in the liquid state.

[0019] The alkoxylation catalyst is preferably a basic catalyst, for example a metal hydroxide, which contains a Group IA or Group IIA metal ion. When the metal ion is a Group IA metal ion, it is a lithium, sodium, potassium or cesium ion, preferably a sodium or potassium ion, and most preferably a potassium ion. When the metal ion is a Group IIA metal ion, it is a magnesium, calcium or barium ion. Examples of the alkoxylation catalyst are lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, calcium hydroxide and barium hydroxide. Sodium hydroxide and potassium hydroxide are preferred catalysts and potassium hydroxide is most preferred. Other suitable alkoxylation catalysts include BF₃, SnCh, sodium phenolate, sodium methoxide, sodium propoxide, BF3-etherate, p-toluene sulfonic acid, fluorosulfonic acid, aluminum butyrate and perchloric acid. The amount of the alkoxylation catalyst is of from 0.01 to 5 wt.%, preferably from 0.05 to 1 wt.%, and more preferably from 0.1 to 0.5 wt.%, based on the total weight of the catalyst, alcohol and alkylene oxide (i.e. the total weight of the final reaction mixture).

[0020] The alkoxylation procedure serves to introduce a desired average number of propylene oxide units per mole of alcohol alkoxylate, wherein different numbers of propylene oxide units are distributed over the alcohol propoxylate molecules. For example, treatment of an alcohol with 13 moles of propylene oxide per mole of primary alcohol results in the alkoxylation of each alcohol molecule with an average of 13 propylene oxide groups, although a substantial proportion of the alcohol will have become combined with more than 13 propylene oxide groups and an approximately equal proportion will have become combined with less than 13. In a typical alkoxylation product mixture, there may also be a minor proportion of unreacted alcohol.

[0021] In one embodiment, the alcohol is treated with a high ratio of moles of propylene oxide to moles of alcohol. For example, the ratio of moles of propylene oxide to moles of alcohol may be at least 7, preferably at least 11 and more preferably at least 13. In many instances, the aqueous solubility of sulfates made from alcohol propoxylates having a high number of propylene oxide groups is lower than desired. The sulfation method of the invention described hereinafter can provide alcohol propoxy sulfates with a high number of propylene oxide groups while also exhibiting a satisfactory aqueous solubility.

[0022] In the above formula (I), x is the number of propylene oxide groups and is of from 1 to 80. The average value for x is of from 1 to 80, preferably of from 3 to 20, and more preferably from 3 to 16. The average number of propylene oxide groups is referred to as the average PO number.

[0023] In one embodiment, the alcohol propoxylate may also contain ethoxylate groups that are added to the alcohol propoxylate by contacting it with ethylene oxide. The ethylene oxide may be added in a step after the propoxylation to provide an EO-tipped molecule or it may be added at the same time as or before the propylene oxide groups are added.

[0024] In one embodiment, a phenolic antioxidant is added to the alcohol propoxylate as a stabilizer, as described in US 2017/0267914, to improve the long term storage stability of the alcohol propoxylate. In another embodiment, the alcohol propoxylate is prepared according to the method described in US 2015/0307428 where the alcohol propoxylate is contacted with a sulfonic acid.

Sulfate and Method of Making

[0025] The alcohol propoxylate R-0-[PO]_x-H, described above, may be sulfated by any known method, for example by contacting the alcohol with a sulfating agent including sulfur trioxide, oleum, complexes of sulfur trioxide with (Lewis) bases, for example the sulfur trioxide pyridine complex and the sulfur trioxide trimethylamine complex, chlorosulfonic acid and sulfamic acid. The sulfation may be carried out at a temperature of at most 80 °C. The sulfation may be carried out at temperature as low as -20 °C. For example, the sulfation may be carried out at a temperature from 10 to 70 °C, preferably from 20 to 60 °C, and more preferably from 20 to 50 °C.

[0026] The alcohol propoxylate may be reacted with a gas mixture which in addition to at least one inert gas contains a gaseous sulfating agent. The amount of sulfating agent is such that the molar ratio of SO3 to alcohol propoxylate is at least 1.14: 1, preferably at least 1.2:1. The molar ratio of SO3 to alcohol propoxylate may be in the range of from 1.2: 1 to 2: 1. In another embodiment, the molar ratio of SO3 to alcohol is at least 1.3: 1. Although other inert gases are also suitable, air or nitrogen are preferred.

[0027] The reaction of the alcohol with the sulfur trioxide containing inert gas may be carried out in falling film reactors. Such reactors utilize a liquid film trickling in a thin layer on a cooled wall which is brought into contact with the gas. Kettle cascades, for example, would be suitable as possible reactors. Other reactors include stirred tank reactors, which may be employed if the sulfation is carried out using sulfamic acid or a complex of sulfur trioxide and a (Lewis) base, for example the sulfur trioxide pyridine complex or the sulfur trioxide trimethylamine complex.

[0028] Following sulfation, the liquid reaction mixture may be neutralized using an aqueous alkali metal hydroxide, for example sodium hydroxide or potassium hydroxide; an aqueous alkaline earth metal hydroxide, for example magnesium hydroxide or calcium hydroxide; a base, for example ammonium hydroxide, substituted ammonium hydroxide, sodium carbonate or potassium hydrogen carbonate; or an amine, for example ethanolamine, diethanolamine, triethanolamine, triethylene tetramine, or tetraethylene pentamine. In one embodiment, a concentrated aqueous alkali hydroxide solution, for example 50% sodium hydroxide solution is used in the neutralization. The neutralization procedure may be carried out over a wide range of temperatures and pressures. For example, the neutralization procedure may be carried out at a temperature from 0 to 90 °C, preferably from 45 to 65 °C and a pressure in the range from 100 to 2000 kPa.

[0029] The alcohol propoxy sulfate may be a liquid, a waxy liquid or a solid at 20 °C. In particular, it is preferred that at least 50 wt.%, preferably at least 60 wt.%, and more preferably at least 70 wt.% of the alcohol propoxy sulfate is liquid at 20 °C. Further, in particular, it is preferred that of from 50 to 100 wt.%, preferably of from 60 to 100 wt.%, and more preferably of from 70 to 100 wt.% of the alcohol alkoxy sulfate is liquid at 20 °C.

[0030] In addition to the main alcohol propoxy sulfate product, the alcohol propoxy sulfate mixture produced in this step will also comprise unreacted alcohol propoxylate and polypropoxy disulfate (PDS). In some embodiments, the alcohol propoxy sulfate product will also comprise polypropoxy hydroxy sulfate (PHS) and/or polypropoxy allyl sulfate (PAS).

[0031] In one embodiment, the sulfation is carried out such that the concentration of unreacted alcohol propoxylate, measured as unreacted organic matter, is less than 10 wt%, preferably less than 6 wt% and more preferably less than 3 wt%. In one embodiment, the sulfation is carried out such that the concentration of PDS is greater than 5 wt%, preferably greater than 7 wt% and more preferably greater than 9 wt%. In one embodiment, the sulfation is carried out such that the concentration of PHS is less than 1 wt%, preferably less than 0.7 wt% and more preferably less than 0.25 wt%.

[0032] These embodiments may occur under separate sulfation conditions or some of these embodiments may occur under the same sulfation conditions. For example, the sulfation may be carried out such that the concentration of unreacted alcohol propoxylate is less than 10 wt% and the concentration of PDS is greater than 5 wt%. Any combination of these concentrations can be achieved by varying the sulfation conditions. These concentrations are based on 100% active surfactant.

[0033] The total concentration of polypropoxy mono and disulfates is calculated by adding the concentration of PHS, PDS and PAS. This total concentration of polypropoxy mono and disulfates may be at least 9 wt%, and preferably at least 12 wt%.

[0034] It is believed that the concentration of the unreacted alcohol propoxylate, PHS, PDS and total polypropoxy (mono and di) sulfates are affected by the molar ratio of the SO3 to the alcohol propoxylate in the feed to the sulfation reactor. It is also believed that lower levels of UOM and higher levels of PDS contribute to improved aqueous solubility of the alcohol propoxy sulfate. cEOR using APS

Hydrocarbon Recovery Composition

[0035] The alcohol propoxy sulfate mixture described above is suitable for use as a surfactant component in a hydrocarbon recovery composition for use in chemical enhanced oil recovery. The method of treating a hydrocarbon containing formation, comprises providing a hydrocarbon recovery composition to at least a portion of the formation and allowing the hydrocarbon recovery composition to contact the formation. The hydrocarbon recovery composition comprising the alcohol propoxy sulfate mixture is typically combined with a hydrocarbon removal fluid to produce an injectable fluid, at the location of a hydrocarbon containing formation, after which the injectable fluid is injected into the hydrocarbon containing formation.

[0036] The alcohol propoxy sulfate mixture may be transported to a hydrocarbon recovery location and stored at that location in the form of an aqueous composition containing for example 15-90 wt.% surfactant. At the hydrocarbon recovery location, the surfactant concentration of such composition would then be further reduced to 0.05-2 wt.%, by diluting the composition with water or brine, before it is injected into a hydrocarbon containing formation. By such dilution with water or brine, an aqueous fluid is formed which can be injected into the hydrocarbon containing formation. Advantageously, a more concentrated aqueous composition having an active matter content of for example 40-90 wt.%, as described above, may be transported to the location and stored there. A further advantage is that the water or brine used in such further dilution, which may originate from the hydrocarbon containing formation (from which hydrocarbons are to be recovered) or from any other source, may have a relatively high concentration of divalent cations, in the above-described ranges. One of the advantages of that is that such water or brine no longer has to be pre-treated (softened) such as to remove the divalent cations, thereby resulting in significant savings in time and costs.

[0037] The hydrocarbon removal fluid comprises 1) water and 2) divalent cations in a concentration of 100 or more parts per million by weight (ppmw). It may also comprise monovalent cations. The water may originate from the hydrocarbon containing formation or from any other source, for example river water, sea water or aquifer water. A suitable example is sea water which may contain 1 ,700 ppmw of divalent cations which typically comprise calcium (Ca²⁺) and magnesium (Mg²⁺) cations. The concentration of divalent cations may be from 100 to 25,000 ppmw, and the concentration of divalent cations may vary greatly between different sources.

[0038] The salinity of the water (e.g. brine), which may originate from the hydrocarbon containing formation or from any other source, may be of from 0.5 to 30 wt.% or 0.5 to 20 wt.% or 0.5 to 10 wt.% or 1 to 6 wt.%. By“salinity” reference is made to the concentration of total dissolved solids (%TDS), wherein the dissolved solids comprise dissolved salts. The salts may be salts comprising divalent cations, for example magnesium chloride and calcium chloride, and salts comprising monovalent cations, for example sodium chloride and potassium chloride. Sea water may have a salinity (%TDS) of 3.6 wt.%.

[0039] The total amount of the surfactants in the injectable fluid may be of from 0.05 to 2 wt.%, preferably 0.1 to 1.5 wt.%, more preferably 0.1 to 1.2 wt.%, most preferably 0.2 to 1.0 wt.%.

Hydrocarbon Containing Formation

[0040] A “hydrocarbon containing formation” is defined as a sub-surface hydrocarbon containing formation. The hydrocarbon containing formation may be a cmde oil-bearing formation. Different cmde oil-bearing formations or reservoirs differ from each other in terms of cmde oil type. First, the API may differ among different cmde oils. Further, different cmde oils comprise varying amounts of saturates, aromatics, resins and asphaltenes. The four components are commonly abbreviated as“SARA”. Further, cmde oils comprise varying amounts of acidic and basic components, including naphthenic acids and basic nitrogen compounds. Still further, cmde oils comprise varying amounts of paraffin wax. These components are present in heavy (low API) cmde oils and light (high API) cmde oils. The overall distribution of such components in a cmde oil is a direct result of geochemical processes. The properties of the cmde oil in the cmde oil-bearing formation may differ widely. For example, in respect of the API and the amounts of the above-mentioned cmde oil components comprising saturates, aromatics, resins, asphaltenes, acidic and basic components (including naphthenic acids and basic nitrogen compounds) and paraffin wax, the cmde oil may be of one of the types as disclosed in WO 2013030140 and US 2016/0177172.

[0041] Hydrocarbons may be produced from hydrocarbon containing formations through wells penetrating such formations.“Hydrocarbons” are generally defined as molecules formed primarily of carbon and hydrogen atoms such as oil and natural gas. Hydrocarbons may also include other elements, such as halogens, metallic elements, nitrogen, oxygen and/or sulfur. Hydrocarbons derived from a hydrocarbon containing formation may include kerogen, bitumen, pyrobitumen, asphaltenes, oils or combinations thereof. Hydrocarbons may be located within or adjacent to mineral matrices within the earth. Matrices may include sedimentary rock, sands, silicilytes, carbonates, diatomites and other porous media. [0042] A hydrocarbon containing formation may include one or more hydrocarbon containing layers, one or more non-hydrocarbon containing layers, an overburden and/or an underburden. An overburden and/or an underburden includes one or more different types of impermeable materials. For example, overburden/underburden may include rock, shale, mudstone, or wet/tight carbonate (that is to say an impermeable carbonate without hydrocarbons). For example, an underburden may contain shale or mudstone. In some cases, the overburden/underburden may be somewhat permeable. For example, an underburden may be composed of a permeable mineral for example sandstone or limestone.

[0043] Properties of a hydrocarbon containing formation may affect how hydrocarbons flow through an underburden/overburden to one or more production wells. Properties include porosity, permeability, pore size distribution, surface area, salinity or temperature of formation. Overburden/underburden properties in combination with hydrocarbon properties, capillary pressure (static) characteristics and relative permeability (flow) characteristics may affect mobilization of hydrocarbons through the hydrocarbon containing formation.

[0044] Fluids (for example gas, water, hydrocarbons or combinations thereof) of different densities may exist in a hydrocarbon containing formation. A mixture of fluids in the hydrocarbon containing formation may form layers between an underburden and an overburden according to fluid density. Gas may form a top layer, hydrocarbons may form a middle layer and water may form a bottom layer in the hydrocarbon containing formation. The fluids may be present in the hydrocarbon containing formation in various amounts. Interactions between the fluids in the formation may create interfaces or boundaries between the fluids. Interfaces or boundaries between the fluids and the formation may be created through interactions between the fluids and the formation. Typically, gases do not form boundaries with other fluids in a hydrocarbon containing formation. A first boundary may form between a water layer and underburden. A second boundary may form between a water layer and a hydrocarbon layer. A third boundary may form between hydrocarbons of different densities in a hydrocarbon containing formation.

[0045] Production of fluids may perturb the interaction between fluids and between fluids and the overburden/underburden. As fluids are removed from the hydrocarbon containing formation, the different fluid layers may mix and form mixed fluid layers. The mixed fluids may have different interactions at the fluid boundaries. Depending on the interactions at the boundaries of the mixed fluids, production of hydrocarbons may become difficult.

[0046] Quantification of energy required for interactions (for example mixing) between fluids within a formation at an interface may be difficult to measure. Quantification of energy levels at an interface between fluids may be determined by generally known techniques (for example spinning drop tensiometer). Interaction energy requirements at an interface may be referred to as interfacial tension.“Interfacial tension” as used herein, refers to a surface free energy that exists between two or more fluids that exhibit a boundary. A high interfacial tension value (for example greater than 10 mN/m) may indicate the inability of one fluid to mix with a second fluid to form a fluid emulsion. As used herein, an“emulsion” refers to a dispersion of one immiscible fluid into a second fluid by addition of a compound that reduces the interfacial tension between the fluids to achieve stability. The inability of the fluids to mix may be due to high surface interaction energy between the two fluids. Low interfacial tension values (for example less than 1 mN/m) may indicate less surface interaction between the two immiscible fluids. Less surface interaction energy between two immiscible fluids may result in the mixing of the two fluids to form an emulsion. Fluids with low interfacial tension values may be mobilised to a well bore due to reduced capillary forces and subsequently produced from a hydrocarbon containing formation. Thus, in surfactant cEOR, the mobilisation of residual oil is achieved through surfactants which generate a sufficiently low crude oil / water interfacial tension (IFT) to give a capillary number large enough to overcome capillary forces and allow the oil to flow.

[0047] Mobilization of residual hydrocarbons retained in a hydrocarbon containing formation may be difficult due to viscosity of the hydrocarbons and capillary effects of fluids in pores of the hydrocarbon containing formation. As used herein“capillary forces” refers to attractive forces between fluids and at least a portion of the hydrocarbon containing formation. Capillary forces may be overcome by increasing the pressures within a hydrocarbon containing formation. Capillary forces may also be overcome by reducing the interfacial tension between fluids in a hydrocarbon containing formation. The ability to reduce the capillary forces in a hydrocarbon containing formation may depend on a number of factors, including the temperature of the hydrocarbon containing formation, the salinity of water in the hydrocarbon containing formation, and the composition of the hydrocarbons in the hydrocarbon containing formation.

[0048] As production rates decrease, additional methods may be employed to make a hydrocarbon containing formation more economically viable. Methods may include adding sources of water (for example brine, steam), gases, polymers or any combinations thereof to the hydrocarbon containing formation to increase mobilization of hydrocarbons.

[0049] In the present invention, the hydrocarbon containing formation is thus treated with a surfactant(s) containing injectable fluid, as described above. Interaction of the fluid with the hydrocarbons may reduce the interfacial tension of the hydrocarbons with one or more fluids in the hydrocarbon containing formation. The interfacial tension between the hydrocarbons and an overburden/underburden of a hydrocarbon containing formation may be reduced. Reduction of the interfacial tension may allow at least a portion of the hydrocarbons to mobilize through the hydrocarbon containing formation.

[0050] The ability of the surfactant(s) containing injectable fluid to reduce the interfacial tension of a mixture of hydrocarbons and fluids may be evaluated using known techniques. The interfacial tension value for a mixture of hydrocarbons and water may be determined using a spinning drop tensiometer. An amount of the surfactant(s) containing injectable fluid may be added to the hydrocarbon/water mixture and the interfacial tension value for the resulting fluid may be determined.

[0051] The temperature of the hydrocarbon containing formation may be 25 °C or higher. The temperature may be in the range of from 25 °C to 200 °C, preferably in a range of from 25 °C to 150 °C, most preferably in a range of from 25 °C to 80 °C. In one embodiment, the temperature of the hydrocarbon containing formation is in the range of from 80 to 120 °C.

[0052] The method of treating a hydrocarbon containing formation comprises providing a hydrocarbon recovery composition to at least a portion of the hydrocarbon containing formation and allowing the hydrocarbon recovery composition to contact the formation wherein the hydrocarbon recover_}' composition comprises alcohol propoxy sulfates, alcohol propoxylates, and polypropoxy disulfate wherein the weight ratio of polypropoxy disulfate to alcohol propoxy sulfates is at least 1:20 and the weight ratio of alcohol propoxylates to alcohol propoxy sulfates is less than 1: 10.

Polymer

[0053] The injectable fluid may also comprise a polymer as further described below. The polymer may be added to the injectable fluid, or to the surfactant containing the alcohol propoxy sulfate mixture before forming the injectable fluid. The main function of the polymer is to increase viscosity. In particular, the polymer may provide mobility control (relative to the oil phase) as the injectable fluid propagates from the injection well to the production well and stimulate the formation of an oil bank that is pushed to such production well.

[0054] Thus, the polymer should be a viscosity increasing polymer such that the polymer should increase the viscosity of an aqueous fluid in which the surfactant has been dissolved, which aqueous fluid may then be injected into a hydrocarbon containing formation. Production from a hydrocarbon containing formation may be enhanced by treating the hydrocarbon containing formation with a polymer that may mobilize hydrocarbons to one or more production wells. The polymer may reduce the mobility of the water phase, because of the increased viscosity, in pores of the hydrocarbon containing formation. The reduction of water mobility may allow the hydrocarbons to be more easily mobilized through the hydrocarbon containing formation.

[0055] Suitable polymers performing the above-mentioned function of increasing viscosity in enhanced oil recovery, for use in the present invention, and preparations thereof, are described in US6427268, US6439308, US5654261, US5284206, US5199490 and US5103909, and also in “Viscosity Study of Salt Tolerant Polymers”, Rashidi et al., Journal of Applied Polymer Science, volume 117, pages 1551-1557, 2010.

[0056] Suitable commercially available polymers for cEOR include Flopaam^® manufactured by SNF Floerger, CIBA^® ALCOFLOOD^® manufactured by Ciba Specialty Additives (Tarrytown, New York), T ramfloc^® manufactured by T ramfloc Inc. (Temple, Arizona) and HE^® polymers manufactured by Chevron Phillips Chemical Co. (The Woodlands, Texas). A specific suitable polymer commercially available at SNF Floerger is Flopaam^® 3630 which is a partially hydrolyzed polyacrylamide.

[0057] The nature of the polymer is not relevant in the present invention, as long as the polymer can increase viscosity. The molecular weight of the polymer should be sufficiently high to increase viscosity. The molecular weight of the polymer is at least 1 million Dalton, preferably at least 2 million Dalton, and more preferably at least 4 million Dalton. The maximum for the molecular weight of the polymer is not essential. The molecular weight of the polymer is at most 30 million Dalton, preferably at most 25 million Dalton.

[0058] Further, the polymer may be a homopolymer, a copolymer or a terpolymer. Still further, the polymer may be a synthetic polymer or a biopolymer or a derivative of a biopolymer. Examples of suitable biopolymers or derivatives of biopolymers include xanthan gum, guar gum and carboxymethyl cellulose.

[0059] A suitable monomer for the polymer, typically a synthetic polymer, is an ethylenically unsaturated monomer of formula R¹ R²C=CR R⁴, wherein at least one of the R¹, R², R³ and R⁴ substituents is a substituent which contains a moiety selected from the group consisting of - C(=0)NH₂, -C(=0)OH, -C(=0)OR wherein R is a branched or linear Ce-C i x alkyl group, -OH, pyrrolidone and -SO3H (sulfonic acid), and the remaining substituent(s), if any, is (are) selected from the group consisting of hydrogen and alkyl, preferably C1-C4 alkyl, more preferably methyl. Most preferably, the remaining substituent(s), if any, is (are) hydrogen. A polymer is preferably used that is made from an ethylenically unsaturated monomer. [0060] Suitable examples of the ethylenically unsaturated monomer as defined above, are acrylamide, acrylic acid, lauryl acrylate, vinyl alcohol, vinylpyrrolidone, and styrene sulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid. Suitable examples of ethylenic homopolymers that are made from the ethylenically unsaturated monomers are polyacrylamide, polyacrylate, polylauryl acrylate, polyvinyl alcohol, polyvinylpyrrolidone, and polystyrene sulfonate and poly(2-acrylamido-2-methylpropane sulfonate). For these polymers, the counter cation for the - C(=0)0 moiety (in the case of polyacrylate) and for the sulfonate moiety may be an alkali metal cation, for example a sodium ion, or an ammonium ion.

[0061] As mentioned above, copolymers or terpolymers may also be used. Examples of suitable ethylenic copolymers include copolymers of acrylic acid and acrylamide, acrylic acid and lauryl acrylate, and lauryl acrylate and acrylamide.

[0062] Preferably, the polymer which may be used in the present invention is a polyacrylamide, more preferably a partially hydrolyzed polyacrylamide. A partially hydrolyzed polyacrylamide contains repeating units of both -[CH2-CHC(=0)NH2]- and -[CH2-CHC(=0)0 M⁺]- wherein M⁺ may be an alkali metal cation, for example a sodium ion, or an ammonium ion. The extent of hydrolysis is not essential and may vary within wide ranges. For example, 1 to 99 mole%, or 5 to 95 mole%, or 10 to 90 mole%, preferably 15 to 40 mole%, and more preferably 20 to 35 mole%, of the polyacrylamide may be hydrolyzed.

Aqueous Solubility of AAS

[0063] As mentioned above, before the alcohol propoxy sulfate mixture is injected into a hydrocarbon containing formation it may be further diluted, generally at the location of the hydrocarbon containing formation. The water or brine may contain significant amounts of divalent cations and may have a relatively high salinity. The alcohol propoxy sulfate mixture should have an adequate aqueous solubility as that improves the injectability of the fluid comprising the surfactant to be injected into the hydrocarbon containing formation. Further, an adequate aqueous solubility reduces loss of surfactant through adsorption to rock within the hydrocarbon containing formation.

[0064] In addition to the alcohol propoxy sulfate mixture being sufficiently soluble, a cosolvent (or solubilizer) may be added to increase the solubility of the surfactants in the hydrocarbon recovery composition and/or in the injectable fluid comprising the composition. Suitable examples of cosolvents are polar cosolvents, including lower alcohols (for example sec- butanol and isopropyl alcohol) and polyethylene glycol. Any amount of cosolvent needed to dissolve the surfactant at a certain salt concentration (salinity) may be easily determined by a skilled person through routine tests.

[0065] A hydrotrope may be added to increase the solubility of the surfactants in the hydrocarbon recovery composition and/or in the below-mentioned injectable fluid comprising the composition. Suitable examples of hydrotropes include both aryl and non-aryl compounds. The aryl compounds are generally aryl sulfonates or short-chain alkyl-aryl sulfonates in the form of their alkali metal salts (for example sodium toluene sulfonate, potassium toluene sulfonate, sodium xylene sulfonate, ammonium xylene sulfonate, potassium xylene sulfonate, calcium xylene sulfonate, sodium cumene sulfonate, and ammonium cumene sulfonate). Suitable examples of non-aryl hydrotropes are sulfonates whose alkyl moiety contains from 1 to 8 carbon atoms (for example butane sulfonate and hexane sulfonate).

[0066] Viscosity modifiers may be added to improve the handling characteristics of the alcohol propoxy sulfate before it is diluted to be used in hydrocarbon recovery. An embodiment of a viscosity modifier is a linear or branched Ci to Ce monoalkylether of mono- or di-ethylene glycol. Suitable examples are diethylene glycol monobutyl ether (DGBE), ethylene glycol monobutyl ether (EGBE) and triethylene glycol monobutyl ether (TGBE). Further, a linear or branched Ci to Ce dialkylether of mono-, di- or triethylene glycol, such as ethylene glycol dibutyl ether (EGDE), may be used as a further viscosity modifier.

Examples

Example 1

[0067] In this example, a number of samples of alcohol propoxy sulfate were evaluated to determine the aqueous solubility and respective amounts of certain other components. The alcohol propoxy sulfate was produced from a C12-C13 alcohol mixture that was propoxylated with an average of 13 propylene oxide groups.

[0068] The samples were produced in a sulfation reactor and the SOValcohol propoxylate molar ratio was varied in the different samples. The amount of unreacted alcohol propoxylate (UOM), measured as unreacted organic matter, polypropoxy hydroxy sulfate (PHS), polypropoxy disulfate (PDS) and total polypropoxy (mono and di) sulfates are provided as a wt% with respect to the alcohol propoxy sulfate. The UOM content was measured using ASTM D3673 and the PHS, PDS and total polypropoxy (mono and di) sulfates content were measured using Time-of- Flight Mass Spectrometry (ToF-MS).

[0069] The aqueous solubility limit of the samples was evaluated with % transmittance measurements using a colorimeter with a 520 nm filter. The samples were analyzed visually to confirm the % transmittance measurements and to check for inhomogeneity in the samples. The aqueous solubility tests were conducted using NaCl brine (with a concentration range of 0.5 to 2.5 wt%) at room temperature (20 °C) and the final surfactant concentration was 0.50% active matter. The samples were evaluated immediately after preparation and after 1 day. Samples A and B are comparative samples.

Table 1

Example 2

[0070] In this example, additional samples of alcohol propoxy sulfate were evaluated to determine the aqueous solubility and respective amounts of certain other components. The alcohol propoxy sulfate was produced from a C12-C13 alcohol mixture that was propoxylated with an average of 13 propylene oxide groups. The samples were produced in a different sulfation reactor and the SCT/alcohol propoxylate molar ratio was varied in the different samples. The UOM, PHS, PDS and total polypropoxy (mono and di) sulfates contents and the aqueous solubility were measured in the same manner as described in Example 1. It is noted in this Example that the UOM was higher in this reactor, but the improvements are still demonstrated in Sample K relative to Samples I and J. Samples I and J are comparative samples.

Table 2

Claims

1. A method of producing alcohol propoxy sulfates comprising sulfating an alcohol propoxylate by contacting the alcohol propoxylate with a sulfating agent under sulfation conditions wherein the sulfation conditions comprise feeding the sulfating agent at a molar ratio of SO3 to alcohol propoxylate of at least 1.14:1.

2. The method of claim 1 wherein the sulfation conditions comprise feeding the sulfating agent at a molar ratio of SO3 to alcohol propoxylate of at least 1.2:1.

3. The method of claim 1 wherein the sulfation conditions comprise feeding the sulfating agent at a molar ratio of SO3 to alcohol propoxylate of at least 1.3:1.

4. The method of claim 1 wherein the sulfation conditions comprise feeding the sulfating agent at a molar ratio of SO3 to alcohol propoxylate of from 1.2: 1 to 2: 1.

5. The method of any of claims 1-4 wherein the sulfating agent is selected from the group consisting of sulfur trioxide, complex of sulfur trioxide with bases, chlorosulfonic acid and sulfamic acid.

6. The method of claim 5 wherein the complex of sulfur trioxide with a base is selected from the group consisting of sulfur trioxide pyridine complex and sulfur trioxide trimethylamine complex.

7. The method of any of claims 1-4 wherein the sulfating agent is sulfur trioxide.

8. The method of any of claims 1-7 wherein the sulfation conditions comprise a temperature in the range of from 10 to 70 °C.

9. A composition comprising alcohol propoxy sulfates, unreacted alcohol propoxylates (UOM), and polypropoxy disulfate (PDS) wherein the concentration of UOM is less than 10 wt% and the concentration of PDS is greater than 5 wt%.

10. The composition of claim 9 wherein the concentration of UOM is less than 6 wt%.

11. The composition of any of claims 9-10 wherein the concentration of PDS is greater than 7 wt%.

12. The composition of any of claims 9-11 wherein the composition also comprises polypropoxy hydroxy sulfate (PHS) and the concentration of PHS is less than 1 wt%.

13. The composition of any of claims 9-12 wherein the composition also comprises polypropoxy allyl sulfates (PAS) and the total concentration of polypropoxy mono and disulfates is greater than 9 wt%.

14. A diluted composition comprising an aqueous diluent and the composition of any of claims 9 to 13 wherein the diluted composition comprises from 0.25 to 1.5 wt% of the composition of any of claims 9 to 13.

15. The diluted composition of claim 14 wherein the aqueous solubility limit of the diluted composition is at least 3 wt% NaCl after 24 hours at room temperature.

16. A method of treating a hydrocarbon containing formation comprising providing a hydrocarbon recover_}' composition to at least a portion of the hydrocarbon containing formation and allowing the hydrocarbon recover_}' composition to contact the formation wherein the hydrocarbon recover_}' composition comprises alcohol propoxy sulfates, alcohol propoxylates, and polypropoxy disulfate wherein the weight ratio of polypropoxy disulfate to alcohol propoxy sulfates is at least 1:20 and the weight ratio of alcohol propoxylates to alcohol propoxy sulfates is less than 1: 10.