GB2169220A

GB2169220A - Preparation of crude oil emulsions

Info

Publication number: GB2169220A
Application number: GB08509482A
Authority: GB
Inventors: Ignacio Layrisse; Alan Stockwell
Original assignee: BP PLC; Intevep SA
Current assignee: BP PLC; Intevep SA
Priority date: 1984-04-12
Filing date: 1985-04-12
Publication date: 1986-07-09
Also published as: CA1274089A; NO175410C; NO175410B; NO851450L; GB8509482D0; GB2169220B

Abstract

An emulsion of crude oil in water is prepared by adding an organic acid containing eight or more carbon atoms per molecule to the crude oil, adding an aqueous alkaline solution and emulsifying the resulting mixture. The viscosity of the emulsion is considerably less than that of the crude. The emulsion is suitable for transportation through a pipeline. As organic acids, aliphatic carboxylic acids with a C8 to C30 alkyl group, eg stearic acid, and petroleum sulphonates, may be used.

Description

SPECIFICATION Preparation of crude oil emulsions This invention relates to a method and a system for the preparation of emulsions of crude oil in water which are suitable for transportation.

Many crude oils are viscous and are thus difficult, if not impossible, to produce and transport by normal methods from their production location to a refinery. Such crude oils often contain asphaltenes and co-produced water, which is frequently saline, dispersed as small droplets. The presence of both these materials acts to increase the viscosity of the crude oil, and the higher their concentrations, the greater the increase in viscosity of the oil.

Several methods have been suggested for the transportation of such crudes by pipeline. These include (1) heating the crude and insulating the pipeline, (2) adding a non-recoverable solvent, (3) adding a recoverable solvent, (4) adding a lighter crude oil, (5) forming an annulus of water around the crude and (6) emulsifying the crude in water. Methods (1)-(4) can be expensive in terms of added components and capital expenditure and method (5) is technically difficult to achieve.

Method (6) whilst superficially attractive presents special difficulties. The dispersion of a highly viscous oil in a medium of much lower viscosity is an unfavourable process on hydrodynamic grounds.

Surfactants are normally required for method (6) and these if used in quantity are expensive. In order to reduce the cost, it has been proposed to add an aqueous alkaline solution to the crude oil and rely on the reaction between the alkaline agent and organic acids present in the crude oil to form surfactants in situ. These then act as emulsifiers for the production of fluid oil-in-water emulsions, see, for example, USP's 4246920 and 4099537. This method suffers from the disadvantage that the in-situ reaction is difficult to control and results in an emulsion which is more viscous than those formed with added surfactants, at similar oil/water ratios. Emulsions prepared from such liquids are relatively unstable and unsuitable for transportation through a pipeline, particularly when the aqueous liquid in which the alkali is dissolved is highly saline.

We have now discovered that adding an organic acid to the crude oil and an aqueous alkaline solution results in the formation of emulsions which have viscosities which are considerably lower than the corresponding crude oils.

Thus according to the present invention there is provided a method for the preparation of an emulsion of crude oil in water which method comprises the steps of adding an organic acid containing eight or more carbon atoms per molecule to the crude oil, adding an aqueous alkaline solution and emulsifying the resulting mixture to form an oil in water emulsion.

Emulsification may be carried out under either low shear or high shear conditions.

Our copending European Patent Application 85300998 discloses a method for the preparation of an HIPR emulsion of oil in water which method comprises directly mixing 70 to 98%, preferably 80 to 90%, by volume of a viscous oil having a viscosity in the range 200 to 250,000 mPa.s at the mixing temperature, with 30 to 2%, preferably 20 to 10%, by volume of an aqueous solution of an emulsifying surfactant or an alkali, percentages being expressed as percentages by volume of the total mixture; mixing being effected under low shear conditions in the range 10 to 1,000, preferably 50 to 250, reciprocal seconds in such manner than an emulsion is formed comprising highly distorted oil droplets having mean droplet diameters in the range 2 to 50 micron separated by thin interfacial films.

It is believed that the acid reacts with the alkaline material to form a surfactant in situ.

Suitable acids can be represented by the following formulae:

wherein R represents a linear or branched chain alkyl group containing 8 to 30 carbon atoms, preferably containing 12 to 20; Ar represents a phenyl, tolyl, xylyl or ethyl phenyl group; n is a number in the range 5 to 20, preferably in the range 10 to 15; and m is a number in the range 0 to 20, preferably in the range Oto 10.

The acids may be used as relatively pure compounds.

Alternatively it is possible to isolate fractions of the produced crude oil and to attach functional groups by chemical reactions. In this way it is possible to form petroleum sulphonic acids, for example. Such acids are equally suitable for use in this invention.

The acid is suitably added in amount 100 to 15,000 ppm, preferably 100 to 5,000 ppm, based on the oil.

The acid can be added to the crude oil either downhole into the reservoir or at the well-head, preferably prior to the addition of the solution of the alkali. It can be added as a solution in crude oil or as a solution in a low molecular weight hydrocarbon such as heptane.

Suitable alkaline agents include alkali metal hydroxides, carbonates, phosphates and silicates; ammonium hydroxide; and alkaline earth metal hydroxides.

Preferably these materials are used dissolved in water in such concentration that the aqueous solution has a pH39.

The water used as the aqueous component of the alkaline solution may be fresh or contain dissolved solids. Connate water associated with the crude oil reservoir can be used. The amount employed should be sufficient to give an emulsion containing 30 to 80% by volume water, expressed as a % by volume of the total emulsion.

The crude oil and alkaline solution may be mixed under conditions known to be suitable for mixing viscous fluids, see H.F. Irving and R.L. Saxton, Mixing Theory and Practice (Eds. V.W. Uhl and J.B. Gray), Vol 1, Chapter 8, Academic Press 1966. Static mixers are also suitable.

The temperature at which the emulsion is formed should not be greater than 150 C.

Emulsions of the desired stability generally have droplet sizes less than 50 microns.

Suitable viscous, heavy and/or asphaltenic crude oils for treatment are to be found in Canada, the USA and Venezuela, for example Lake Marguerite crude oil from Alberta, Hewitt crude oil from Oklahoma and Cerro Negro crude oil from the Orinoco oil belt.

Generally the API gravity is in range 5" to 15 , although the method can be applied to crude oils outside this range. For example the method can also be applied to non-asphaltenic crude oils such as Beatrice from the UK sector of the North Sea. This crude oil (30 API) is viscous because of its high wax content and the subsequent gel structure developed by intermolecular association of wax components.

It will generally be found that the viscosity of the crude oils can be reduced by a factor of 1,000 to 10,000 times following emulsification.

The emulsions are suitable for transportation through a pipeline and represent an elegant solution to the problem of transporting viscous crude oils.

Thus according to a another aspect of the present invention there is provided a method for the transportation of a viscous crude oil which method comprises the steps of preparing an emulsion of the crude oil in water by a method as hereinbefore described and pumping the emulsion through a pipeline.

After transportation through the pipeline, the oil and water may be separated by emulsion breaking and dehydration of the crude oil.

According to a further aspect of the invention there is provided a system for the preparation and transportation of an emulsion of crude oil in water by a method which comprises the steps of adding an organic acid containing eight or more carbon atoms per molecule to the crude oil, adding an aqueous alkaline solution and emulsifying the resulting mixture to form an oil in water emulsion wherein the system comprises (a) a storage tank for the organic acid, (b) a storage tank for the aqueous alkaline solution, (c) a line leading directly or indirectly from (a) to a line (e) as hereinafter defined, (d) a line leading directly or indirectly from (b) to the line (e), (e) a line for transporting the emulsion of crude oil in water, and (f) means for emulsifying the mixture of organic acid, aqueous alkaline solution and crude oil to form the emulsion.

When both lines (c) and (d) or line (d) along lead or leads directly to line (e), the means for emulsifying the mixture may be a static mixer or a mixing valve.

If both lines (c) and (d) or line (c) alone lead or leads indirectly to line (e), then lines (c) and (d) or line (c) may lead to injection wells to the crude oil reservoir, thereby injecting acid and alkaline solution, or acid alone into the crude oil before production. In the first case, the reservoir itself is the means for emulsifying the mixture.

Alternatively, line (c) may lead to an outer annulus of a production well, thereby injecting acid into the crude oil at the point of production.

The invention is illustrated with reference to the accompanying drawing which is a schematic representation of a system for the preparation and transportation of an emulsion of a heavy crude oil in water, and to the following Example.

Organic acid is held in a storage tank 1 in which it is dissolved in a suitable solvent which can be the crude oil itself or a fraction of it. The alkaline solution is held in a storage tank 2.

Lines 3 and 4 lead from tanks 1 and 2 to injection wells 5 and 6 injecting into a crude oil reservoir 7.

The alkali may be added as part of an alkaline flood.

Alternatively the acid may be added through line 8 and down the outer casing of a production well 9 or through line 10 into the offtake 11 from the well. In either case the alkali is added directly through line 12.

The emulsion is formed either by natural mixing in the reservoir, production well bore or well head, or by the in-line mixer 13 or mixing valve 14.

Injection facilities can be used in the following combinations: 10 with 12; 8 with 12; 5 with 12; 5 with 6; 6 with 8 and 6 with 10.

Example Cerro Negro crude oil was used. This is a heavy crude oil having an API Gravity of 8.1", a water content of 0% and a viscosity of 2 x 105 cP at 25"C. It is a Newtonian liquid.

40 parts by volume of an aqueous solution containing 5,000 ppm sodium chloride and sufficient sodium hydroxide to give a pH of 12.2 were poured into the mixing chamber of a Waring blender.

60 parts by volume of crude oil containing 1% by wt stearic acid were then added to the same chamber.

The mixture was homogenised at room temperature for three minutes at full speed, approximately 15,000 rpm.

After allowing the foam to settle, a representative sample of the emulsion was taken and placed in the measuring cup of a Contraves Low Shear 30 Viscometer. The emulsion is a non-Newtonian liquid and its viscosity was measured at different shear rates at 25"C.

The following results were obtained Shear Rate Viscosity y(sec-l) (cP) 0.06 40.8 0.29 21.0 1.34 11.2 6.06 8.2 27.0 7.2

Claims

1. A method for the preparation of an emulsion of crude oil in water which method comprises the steps of adding an organic acid containing eight or more carbon atoms per molecule to the crude oil, adding an aqueous alkaline solution and emulsifying the resulting mixture to form an oil in water emulsion.

2. A method according to claim 1 wherein the acid is an aliphatic carboxylic acid containing an alkyl group containing 8 to 30 carbon atoms.

3. A method according to claim 1 wherein the acid is a petroleum sulphonate.

4. A method according to any of the preceding claims wherein the aqueous alkaline solution contains an alkali metal hydroxide, carbonate, phosphate or silicate; ammonium hydroxide or an alkaline earth metal hydroxide.

5. A method according to any of the preceding claims wherein the API gravity of the crude oil is in the range 5" to 15 .

6. A method for the transportation of a viscous crude oil which method comprises the steps of preparing an emulsion of the crude oil in water by a method according to any of the preceding claims and pumping the emulsion through a pipeline.

7. A system for the preparation and transportation of an emulsion of crude oil in water by a method which comprises the steps of adding an organic acid containing eight or more carbon atoms per molecule to the crude oil, adding an aqueous alkaline solution and emulsifying the resulting mixture to form an oil in water emulsion wherein the system comprises: (a) a storage tank for the organic acid, (b) a storage tank for the aqueous alkaline solution, (c) a line leading directly or indirectly from (a) to a line (e) as hereinafter defined, (d) a line leading directly or indirectly from (b) to the line (e), (e) a line for transporting the emulsion of crude oil in water, and (f) means for emulsifying the mixture of organic acid, aqueous alkaline solution and crude oil to form the emulsion.

8. A system according to claim 7 wherein line (d) leads directly to line (e) and the means for emulsifying the mixture is a static mixer or a mixing valve.

9. A method according to claim 1 as hereinbefore described with reference to the Example.