Patent Application
20120241151
The present invention relates to processes for mineral oil production, in which an aqueous surfactant formulation comprising at least one alkyl polyglucoside is injected into a mineral oil deposit through at least one injection borehole and crude oil is withdrawn from the deposit through at least one production borehole, wherein the formulation does not comprise any alcohols as cosolvents.
In natural mineral oil deposits, mineral oil is present in the cavities of porous reservoir rocks which are sealed toward the surface of the earth by impervious top layers. The cavities may be very fine cavities, capillaries, pores or the like. Fine pore necks may, for example, have a diameter of only about 1 μm. As well as mineral oil, including fractions of natural gas, a deposit comprises water with a greater or lesser salt content.
In mineral oil production, a distinction is generally drawn between primary, secondary and tertiary production. In primary production, the mineral oil flows, after commencement of drilling of the deposit, of its own accord through the borehole to the surface owing to the autogenous pressure of the deposit.
After primary production, secondary production is therefore used. In secondary production, in addition to the boreholes which serve for the production of the mineral oil, the so-called production boreholes, further boreholes are drilled into the mineral oil-bearing formation. Wafer is injected into the deposit through these so-called injection boreholes in order to maintain the pressure or to increase it again. As a result of the injection of the water, the mineral oil is forced slowly through the cavities into the formation, proceeding from the injection borehole in the direction of the production borehole. However, this only works for as long as the cavities are completely filled with oil and the more viscous oil is pushed onward by the water. As soon as the mobile water breaks through cavities, it flows on the path of least resistance from this time, i.e. through the channel formed, and no longer pushes the oil onward.
By means of primary and secondary production, generally only approx. 30 to 35% of the amount of mineral oil present in the deposit can be produced.
It is known that the mineral oil yield can be enhanced further by measures for tertiary oil production. A review of tertiary oil production can be found, for example, in “Journal of Petroleum Science of Engineering 19 (1998)”, pages 285 to 280. Tertiary oil production includes thermal methods in which hot water or steam is injected into the deposit. This lowers the viscosity of the oil. The flow medium used may likewise be gases such as CO2 or nitrogen.
Tertiary mineral oil production also includes methods in which suitable chemicals are used as assistants for oil production. These can be used to influence the situation toward the end of the water flow and as a result also to produce mineral oil hitherto held firmly within the rock formation.
Viscous and capillary forces act on the mineral oil which is trapped in the pores of the deposit rock toward the end of the secondary production, the ratio of these two forces relative to one another being determined by the microscopic oil separation. By means of a dimensionless parameter, the so-called capillary number, the action of these forces is described. It is the ratio of the viscosity forces (velocity×viscosity of the forcing phase) to the capillary forces (interfacial tension between oil and water×wetting of the rock):
In this formula, μ is the viscosity of the fluid mobilizing mineral oil, ν is the Darcy velocity (flow per unit area), σ is the interfacial tension between liquid mobilizing mineral oil and mineral oil, and θ is the contact angle between mineral oil and the rock (C. Melrose, C. F. Brandner, J. Canadian Petr. Techn., 58, October-December 1974). The higher the capillary number, the greater the mobilization of the oil and hence also the degree of oil removal.
It is known that the capillary number toward the end of secondary mineral oil production is in the region of about 10−6 and that it is necessary to increase the capillary number to about 10−3 to 10−2 in order to be able to mobilize additional mineral oil.
With the aid of surfactants, the oil-water interface can be covered and the interracial tension σ can more preferably be lowered to values of <10−2 mN/m (ultralow interfacial tension).
In this manner, it is possible to alter the form of the oil droplets (interracial tension between oil and water is lowered to such a degree that the smallest interface state is no longer favored and the spherical form is no longer preferred), and they can be forced through the capillary openings by the flooding water.
Typically, the surfactants are optionally injected together with cosolvents and/or basic salts (optionally in the presence of chelating agents). Subsequently, a solution of thickening polymer is injected for mobility control. A further variant Is the injection of a mixture of thickening polymer and surfactants, cosolvents and/or basic salts (optionally with chelating agent), and then a solution of thickening polymer for mobility control. These solutions should generally be clear in order to prevent blockages of the reservoir.
The requirements on surfactants for tertiary mineral oil production differ significantly from requirements on surfactants for other applications: suitable surfactants for tertiary oil production should reduce the interfacial tension between water and oil (typically approx. 20 mN/m) to particularly low values of less than 10−2 mN/m in order to enable sufficient mobilization of the mineral oil. This has to be done at the customary deposit temperatures of approx. 15° C. to 130° C. and in the presence of wafer of high salt content, more particularly also in the presence of high proportions of calcium and/or magnesium ions; the surfactants thus also have to be soluble in deposit water with a high salt content.
To fulfill these requirements, there have already been frequent proposals of mixtures of surfactants, especially mixtures of anionic and nonionic surfactants. Nonionic surfactants, for example of the alkyl polyglucoside type, have been described, but the low interfacial tensions required had been attained only by addition of significant amounts of cosolvents, for example an alcohol.
U.S. Pat. No. 4,985,154 describes a mixture of alkyl polyglucosides with cosolvents for use in oil production. The cosolvents mentioned include various alcohols (column 8 lines 4 ff.), for example monoalcohols having 3 to 8 carbon atoms, polyalcohols having 3 to 10 carbon atoms, alkyl ethers of polyalcohols having 2 to 8 carbon atoms in the alkyl chain, or alkyl polyglucosides with alkyl chains of 3 to 8 carbon atoms in length. At column 5 line 10 it is pointed out that a cosolvent is always required when alkyl polyglucosides are used. The surfactant/cosolvent ratio is preferably 1:5 to 5:1. The examples disclose aqueous surfactant formulations in which the amount of surfactant and cosolvent is in each case 4% by weight.
US 2008/048948 claims the mixture of alkyl polyglucosides with aromatic alcohols for tertiary mineral oil production. The mixing ratio of the aromatic alcohol with the alkyl polyglucosides may be 1000:1 to 1:1000. In addition, table 9 (page 9) discloses combinations of the aliphatic alcohols 1-propanol, 1-butanol, 1-hexanol or 1-octanol with a C12-based alkyl polyglucoside in a weight ratio of 1:3, which attains the required interfacial tensions with octane as a model oil. A low interracial tension without addition of alcohol was not found.
S. Iglauer, Y. Wu, P. Shuler, Y. Tang and W. A. Goddard III, Colloids and Surfaces A: Physichochem. Eng. Aspects 339 (2009) 48-59 disclose formulations composed of alkyl polyglucosides and various alcohol cosolvents for improved mineral oil production. The cosolvents used were, for example, 1-propanol, 1-butanol, 1-hexanol, 1-octanol, 1-dodecanol, 4-methyl-2-hexanol cyclohexanol or phenol or naphthol. For the tests, in each case 2% by weight of a mixture of surfactant and cosolvent was used; the minimum amount used was 10% alcohol based on the mixture of alcohol and surfactant in the case of use of 1-dodecanol; for the other alcohols it was at least 20% by weight. The use of alkyl polyglucosides in an amount of 2% by weight in a model system composed of salt-containing water (2% NaCl) and n-octanol, but without addition of alcohols as cosolvents, led only to oil-water interfacial tensions at room temperature of 0.735 mN/m (in the case of an alkyl polyglucoside with one alkyl group having an average of 12.5 carbon atoms), 1.08 mN/m-(with an average of 10.1 carbon atoms) and 2.4 mN/m (with an average of 9.1 carbon atoms).
WO 2009/124922 discloses alkyl polyglucosides based on branched C17-alcohols and the use thereof for tertiary mineral oil production.
The use parameters, for example type, concentration and the mixing ratio of the surfactants used relative to one another, are therefore adjusted by the person skilled in the art to the conditions prevailing in a given oil formation (for example temperature and salt content).
As described above, mineral oil production is proportional to the capillary number. The lower the interfacial tension between oil and water, the higher this is. The addition of alcohols as a cosolvent to surfactants can lower the interfacial tension provided that the alcohol has a sufficient number of carbon atoms. In addition to the increased costs resulting from the addition of further chemicals, there is the disadvantage that hydrophobic nonionic compounds such as alcohols have good solubility in the oil phase. On contact of the surfactant formulation with the oil, the alcohol is effectively extracted away from the interface. This alters the composition of the compounds at the oil-water boundary and the interfacial tension rises again. Only in the case of use of high amounts of surfactant and alcohol would the “production” be barely noticeable.
It is therefore an object of the invention to provide a particularly efficient surfactant or an efficient surfactant mixture for use for surfactant flooding, and an improved process for tertiary mineral oil production.
It has been found that, surprisingly, the addition of alcohols as a cosolvent is unnecessary to achieve low interfacial tensions with respect to crude oils in the case of use of surfactants of the general formula (I).
Accordingly, a process for mineral oil production has been found, in which an aqueous surfactant formulation is injected into a mineral oil deposit through at least one injection borehole and crude oil is withdrawn from the deposit through at least one production borehole, the interfacial tension between oil and water in the deposit being lowered to values of <0.1 mN/m in the presence of said surfactant formulation, and said aqueous surfactant formulation comprising at least
In a preferred embodiment,
In a particularly preferred embodiment:
With regard to the invention, the following should be stated explicitly:
In the process according to the invention as described above for mineral oil production, an aqueous surfactant formulation comprising at least one surfactant is used.
According to the invention, the aqueous formulation comprises at least one surfactant of the general formula
R1O—(A)m—H (I).
It will be appreciated that it is also possible to use two or more surfactants of the formula (I).
The R1 radical from the general formula (I) is a linear or branched, saturated or unsaturated, aliphatic or aromatic-aliphatic hydrocarbyl radical having 8 to 24 carbon atoms, preferably 8 to 18 carbon atoms, Particular preference is given to linear, saturated or unsaturated, aliphatic hydrocarbyl radicals having 8 to 18 carbon atoms. Examples thereof are the radicals of fatty alcohols and/or mixtures thereof.
In the above formula (I), A is defined as the radical of a hexose or pentose residue. Examples of hexoses are allose, altrose, glucose, mannose, gulose, idose, galactose or talose. Examples of pentoses are ribose, arabinose, xylose or lyxose. The selection of the sugars is made by the person skilled in the art depending on the alcohol used and the desired target compounds and profile of properties. A is preferably the radical of glucose and/or xylose residues, and A is more preferably a glucose residue.
In the case of hexoses, the general formula of the surfactants is R1O—(C8H10O5)m—H (II), One of the OH groups of a hexose has been esterified with an alcohol R1OH and the m sugar units are joined to one another via glycosidic bonds in a manner known in principle.
In the above-defined general formula, m may be an integer. However, it is clear to the person skilled in the art in the field of alkyl polyglucosides that this definition is the definition of one single surfactant in each case. In the case of presence of surfactant mixtures or surfactant formulations which comprise several surfactants of the general formula, the number m is an average over all molecules of the surfactants since the reaction of alcohol with hexoses or pentoses always gives a certain distribution of chain lengths. This distribution can be described in a manner known in principle by what is called the polydispersity D. D=Mw/Mn is the quotient of the weight-average molar mass and the number-average molar mass. The polydispersity can be determined by means of methods known to those skilled in the art, for example by means of gel permeation chromatography.
In the above general formula, m is from 1 to 10, preferably 1 to 3, more preferably 1 to 2.
The surfactants of the general formula (I) can be prepared in a manner known in principle by acid-catalyzed reaction of alcohols R1OH (II) with sugars while removing the water of reaction. Illustrative descriptions can be found inter alia in U.S. Pat. No. 3,547,828 or U.S. Pat. No. 5,898,070.
As a by-product, the surfactants of the general formula (I) may also comprise residues of the alcohols R1OH, where the R1 radicals in the formulae (I) and (II) are identical. Such alcohol contents can be obtained by an incomplete conversion in the course of the synthesis mentioned and need not be removed.
According to the invention, the at least one surfactant R1O—(A)m—H (I), however, comprises not more than 3% by weight, based on the amount of the surfactant, of the alcohol R1OH (II), preferably not more than 1.5% by weight.
In addition to the surfactants of the general formula (I), the formulation may additionally optionally also comprise further surfactants. Examples of such surfactants comprise anionic surfactants of the alkylarylsulfonate or olefinsulfonate (alpha-olefinsulfonate or internal olefinsulfonate) type, alkyl alkoxy sulfate type, alkyl alkoxy sulfonate type, alkyl alkoxy carboxylate type, and/or nonionic surfactants of the alkyl ethoxylate type. It is also possible to use betaine surfactants.
According to the invention, the surfactant formulation used comprises, as a solvent, at least 50% by weight of water, preferably at least 80% by weight, more preferably at least 90% by weight of water and most preferably at least 95% by weight, based on the amount of all components of the formulation.
It may additionally optionally also comprise water-miscible cosolvents, though the cosolvents do not include the alcohols R1OH already mentioned.
According to the invention, however, cosolvents exclude the following compounds having OH groups:
More preferably, the formulation does not comprise any cosolvent apart from water.
In addition to the surfactants, solvents, optionally cosolvents and cosurfactants, the formulations described may also comprise further components or additives, for example salts or complexing agents such as EDTA.
In a particularly preferred embodiment, the formulation additionally comprises basic salts (what is called “alkali surfactant flooding”). Such salts may be selected from the group of the alkali metal hydroxides, alkali metal silicates or alkali metal carbonates, preferably from alkali metal hydroxides and alkali metal carbonates. With such additions, for example, retention in the formation can be reduced. Advantageously, the addition of basic salts converts acidic compounds in the mineral oils, especially naphthenic acids which occur in the mineral oil, to the corresponding salts, which gives rise to a natural surfactant action. The lowering of the interfacial tension is thus caused not only by the alkyl polyglucosides alone, but is promoted by natural surfactants. The amount of basic salts may typically be from 0.1% by weight to 5% by weight based on the total amount of ail components of the aqueous formulation. Examples of preferred basic salts comprise sodium carbonate or sodium hydroxide. A formulation comprising basic salts may also advantageously comprise complexing agents, for example EDTA.
The total concentration of all surfactants together is generality 0.01 to 5% by weight based on the total amount of the aqueous surfactant formulation, preferably 0.05 to 2.5% by weight and more preferably 0.1 to 2% by weight.
The amount of the surfactants of the surfactants used in accordance with the invention general formula R1O—(A)m—H (I) is generally at least 0.01% by weight, preferably at least 0.05% by weight and more preferably at least 0.1% by weight.
In general, the proportion of the surfactants of the general formula (I) is at least 50% by weight, preferably at least 80% by weight, more preferably at least 90% by weight and most preferably 100% by weight of all surfactants used, i.e. exclusively surfactants of the general formula (I) are used.
The deposits in which the process is employed generally have a temperature of at least 10° C., for example 10 to 150° C., especially a temperature of at least 15° C. to 120° C. The process is especially suitable for deposits with elevated deposit temperature, especially deposits at 40° C. to 120° C., preferably 45° C. to 110° C. and more preferably 50° C. to 100° C.
In a known manner, the deposit comprises oil and deposit water, which generally has a greater or lesser salt content.
The oil may comprise light, medium or heavy oils, for example those with an API gravity of 10° to 45° API (as defined by the American Petroleum Institute).
The deposits may preferably be those with salt contents of the deposit wafer of more than 30 000 ppm. The salts may especially be alkali metal salts and alkaline earth metal salts. Examples of typical cations comprise Na30, K+, Mg2+ or Ca2+, and examples of typical anions comprise chloride, bromide, hydrogencarbonate, sulfate or borate.
For deposits containing oil of API gravity from 10° API to less than 30° API, it is particularly advantageously possible to use formulations which comprise the basic salts mentioned, especially alkali metal hydroxides or carbonates, and most preferably sodium hydroxide or sodium carbonate.
For deposits with an API gravity of 30° to 45° API, deposit temperatures of >40° C. and more than 30 000 ppm of salts, it is also possible to efficiently use formulations which do not comprise any basic salts.
In the process according to the invention for mineral oil production, the aqueous surfactant formulation described is injected into the mineral oil deposit through at least one injection borehole and crude oil is withdrawn from the deposit through at least one production borehole. In this context, the term “crude oil” of course does not mean single-phase oil, but means the customary crude oil-water emulsions. In general, a deposit is provided with several injection boreholes and with several production boreholes.
The main effect of the surfactant of the formula (I) and of optionally used cosurfactants lies in the reduction of the interfacial tension between water and oil. In the performance of the process according to the invention for tertiary mineral oil production, the use of the surfactant mixture described lowers the interfacial tension between oil and water to values of <0.1 mN/m, preferably to <0.05 mN/m, more preferably to <0.01 mN/m. Thus, the interfacial tension between oil and water is lowered to values in the range from 0.1 mN/m to 0.0001 mN/m, preferably to values in the range from 0.05 mN/m to 0.0001 mN/m, more preferably to values in the range from 0.01 mN/m to 0.0001 mN/m.
The amount of the formulation to be injected is guided by the pore volume in the region of the mineral oil formation covered by the flooding operation, i.e. the region between the injection borehole and the production borehole. The pore volume can be determined by means of known methods. In general, it is advisable to inject, as the surfactant flood, an amount of 0.05 to 3 times the pore volume.
After the injection of the surfactant formulation, called the “surfactant flooding”, the pressure can be maintained by injecting water into the formation (“water flooding”) or preferably a higher-viscosity aqueous solution of a polymer with strong thickening action (“polymer flooding”). However, there are also known techniques by which the surfactants are first of ail allowed to act on the formation. A further known technique is the injection of a solution of surfactants and thickening polymers, followed by a solution of thickening polymer. The person skilled in the art is aware of details of the industrial performance of “surfactant flooding”, “water flooding” and “polymer flooding”, and he employs an appropriate technique according to the type of deposit.
The person skilled in the art makes a suitable selection with regard to the concentration of surfactants according to the desired properties, especially according to the conditions in the mineral oil formation. The amount is especially such that the required reduction in the interfacial tension to values below 0.1 mN/m is achieved. It will be clear to the person skilled in the art here that the concentration of the surfactants can alter after the injection into the formation because the formulation can mix with formation water, or surfactants can also be absorbed at solid surfaces of the formation. It is a great advantage of the mixture used in accordance with the invention that the surfactants lead to a particularly good lowering of interfacial tension.
It is of course possible first to produce a concentrate which is only diluted to the desired concentration for injection info the formation once on site, in general, the total concentration of the surfactants in such a concentrate is 30 to 50% by weight. According to the surfactant, however, concentrates up to 98% can also be supplied, but storage is in that case sometimes required at 40-50° C.,
The examples which follow are intended to illustrate the invention in detail:
Synthesis of the Surfactants Used in Accordance with the Invention
Compounds of the general formula (I) were prepared as described in U.S. Pat. No. 5,898,070, example 1.
The sugars used for the synthesis were D-glucose monohydrate and the following alcohols.
In the surfactants of the formula R1O—(A)m—H thus obtained, A is glucose residues and m is 1.4 to 1.9. The residual alcohol content R1OH is in each case less than 2% by weight based on the surfactants R1O—(A)m—H.
For the comparative tests, the commercially available surfactants octylsulfate sodium salt, dodecylbenzenesulfonate sodium salt, lauryl alcohol alkoxylated with 10 units of ethylene oxide, laurylamine oxide and cocoamidopropylbetaine were used.
The surfactants obtained were used to measure interfacial tensions by means of a spinning-drop technique, in order to assess suitability of the surfactants for tertiary mineral oil production. Subsequently, pilot tests were conducted on a smaller scale.
Interfacial tensions were measured by spinning-drop tensiometer. For this purpose, a crude oil and 1% by weight of surfactant in seawater (with a salinity of >30 000 ppm) were used at SOX. The interfacial tension was determined after a spinning time of 1 minute. The results are reproduced in table 1. The examples C1-C5 serve for comparison.
As can be seen in table 1, the surfactant solutions used in accordance with the invention attain very low interfacial tensions under the test conditions, even though no cosolvent was added (examples 1 and 2). Remarkably, the nonionic surfactants of the general formula (I) under these conditions achieve much lower interfacial tensions than other commercial surfactants (examples C1-C5).
In order to test the action in an oilfield, the above surfactants, again as 1% solutions in water, were injected into a formation through one or more injectors by means of customary methods, and crude oil was withdrawn via the production borehole. After the surfactant flood, a buffer and water were injected. The amount of oil produced for the producer depends on the surfactant used and the pore volume of surfactant solution injected.
The results are reproduced in table 2. Examples C8 to C10 serve for comparison. The table shows the proportion of the mineral oil produced after the injection of aqueous surfactant formulation into the formation, specifically after injection of an amount which corresponds to the pore volume in the flooded region of the formation, and after the injection of 1.5 times and 2 times the amount. The term “pore volume” (PV) is described in detail in U.S. Pat. No. 3,927,718.
As can be seen in table 2, the results from the interfacial tension measurements are confirmed. Even without addition of cosolvents, alkyl polyglucosides deliver significant amounts of oil which are higher than for other surfactants.
| Number | Date | Country | |
|---|---|---|---|
| 61466997 | Mar 2011 | US |
