EP0175879B1 - Transportation of viscous crude oils - Google Patents

Description

Heavy oils are difficult to transport in pipelines under conditions of usual outside temperatures due to their very high viscosity. To increase their mobility, they are therefore often mixed with low-viscosity crude oils or refinery cuts; such a procedure requires relatively high additives in order to achieve a noticeable improvement in flow. In addition, such a process is only possible where light oil fields exist at the same location or where a nearby refinery can supply low-viscosity gasoline fractions.

Another method also used is to add heat to the heavy oil in order to lower its viscosity and accordingly improve its fluidity, which requires considerable amounts of heat. So it is z. B. necessary to heat a heavy oil of 10.3 ° API, whose viscosity at 20 ° C is 40 000 mPa - s, to a temperature of approx. 95 ° C in order to achieve a viscosity of approx. 100 mPa · one for the oil transport in pipelines frequently required threshold value (ML Chirinos et al, Rev. Tec. Intevep 3 (2), 103 (1983). This means an extreme cost for the equipment and the supply of the pipelines and a loss of 15 to 20% Crude oil, since the necessary amount of heat is usually obtained by burning crude oil.

Another method of heavy oil transport consists in pumping the oil through the pipes in the form of a more or less easily liquid emulsion. Since the viscosity of emulsions is largely determined by that of the dispersing agent, this is an oil-in-water emulsion. The oil-in-water emulsion is obtained by adding water and emulsifier to the oil using shear forces and then pumping this mixture into the pipeline. In a settling tank, e.g. B. before entering the refinery, the emulsion is separated again in oil and water and the separated oil is fed to the refinery. The lowest possible concentration of the emulsifier should lead to a stable, slightly liquid oil-in-water emulsion with a very high oil content, which naturally places high demands on the emulsifiers to be used. High shear forces should also be avoided during emulsification, since there is a risk of inversion to a water-in-oil emulsion that is extremely highly viscous in heavy oils. The emulsions are also said to be stable both to higher salinities such as occur in many deposit systems and to higher temperatures. Despite the stability of the emulsions as they flow through the pipeline, they should be able to be separated again without any problems. Sulfur-containing emulsifiers are undesirable if they fail to be kept in the aqueous phase during the cleavage.

The previously proposed emulsifiers do not yet meet the stated conditions sufficiently. In many cases (e.g. US Pat. Nos. 4,285,356, 4,265,264, 4,249,554) emulsions with oil contents of only 50% are mentioned, which means that half of the pipeline volume has to be dispensed with. In other cases (eg CA patents 1 108 205, 1 113529, 1 117 568 and US Pat. No. 4 246 919) the viscosity reduction achieved with the emulsifier additive is small despite the relatively low oil content. Finally, undesirable sulfur-based emulsifiers are often used.

There was therefore the task of finding emulsifiers for the emulsification of heavy oil for transporting heavy oil in pipelines which do not have the disadvantages mentioned but essentially correspond to the property catalog described above.

in der R einen linearen oder verzweigten aliphatischen Rest mit 6 bis 20 Kohlenstoffatomen, einen alkyl-oder dialkylaromatischen Rest mit 5 bis 16 Kohlenstoffatomen pro Alkylgruppe, n 1 bis 40 und M ein Alkali- oder Erdalkali-Metallion oder Ammonium bedeuten, einsetzt.This object is achieved in that carboxymethylated oxyethylates of the formula are used as emulsifiers

in which R is a linear or branched aliphatic radical having 6 to 20 carbon atoms, an alkyl or dialkyl aromatic radical having 5 to 16 carbon atoms per alkyl group, n is 1 to 40 and M is an alkali metal or alkaline earth metal ion or ammonium.

mit Chloressigsäure oder einem Salz der Chloressigsäure in Gegenwart von Alkalihydroxid oder Erdalkalihydroxid her. Aber auch andere Herstellungsverfahren sind geeignet. R bedeutet vorzugsweise einen gesättigten oder ungesättigten, geradkettigen oder verzweigten Alkylrest mit 8 bis 18 C-Atomen oder einen Alkylarylrest mit 5 bis 16 C-Atomen in der Alkylgruppe oder einen Dialkylrest mit 3 bis 16 C-Atomen pro Alkylgruppe. Als Alkohole, deren Oxethylate carboxymethyliert werden, lassen sich z. B. einsetzen : Hexylalkohol, Octylalkohol, 2-Ethylhexylalkohol, Nonylalkohol, Isononylalkohol, Decyl- und Undecylalkohol, Lauryl-, Tridecyl-, Myristil-, Palmityl- und Stearylalkohol, aber auch ungesättigte, wie z. B. Oleylalkohol.The carboxymethylated oxyethylates according to DE-PS 24 18 444 are advantageously prepared by reacting oxethylates of the formula

with chloroacetic acid or a salt of chloroacetic acid in the presence of alkali hydroxide or alkaline earth hydroxide. However, other manufacturing processes are also suitable. R is preferably a saturated or unsaturated, straight-chain or branched alkyl radical having 8 to 18 carbon atoms or an alkylaryl radical having 5 to 16 carbon atoms in the alkyl group or a dialkyl radical having 3 to 16 carbon atoms per alkyl group. As alcohols whose oxethylates are carboxymethylated, z. B. use: hexyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl alcohol, decyl and undecyl alcohol, lauryl, tridecyl, myristile, palmityl and stearyl alcohol, but also unsaturated, such as. B. oleyl alcohol.

Commercially available mixtures of these alcohols can be expedient. Can be used as alkylphenols e.g. B. Use: pentylphenol, hexylphenol, octylphenol, nonylphenol, dodecylphenol, hexadecylphenol and the corresponding dialkylphenols. Alkyl cresols and xylenols are also suitable.

kann Natrium, Kalium, Lithium, Ammonium, Calcium, Magnesium oder Wasserstoff sein.The oxethylation can be carried out in the presence of catalytic amounts of alkali metal hydroxide, but it is known that other processes are also possible. The degree of oxyethylation can assume values between 1 and 40, preferably between 3 and 20. The cation in carboxymethylated oxethylate with the formula

can be sodium, potassium, lithium, ammonium, calcium, magnesium or hydrogen.

The emulsifiers used are predominantly anionic, so that an unproblematic cleavage of the emulsion stabilized by them can be assumed. The compounds are thermally stable and compatible with salt water within extremely wide limits (US Pat. No. 4,457,373). Furthermore, by varying the hydrophobic residue and the degree of oxyethylation, they allow the emulsifier to be optimally adapted to the oil to be transported and the given salinity of the water conveyed from the deposit in most cases, which advantageously forms the aqueous phase of the emulsion to be transported.

bezeichnet daher ein Gemisch mit unterschiedlichen Mengen an nicht umgesetztem Oxyethylat, sofern der Carboxymethyllerungsgrad zwischen 40 und 100 %, vorzugsweise zwischen 50 und 100 %, liegt.According to their production, the carboxymethylated oxethylates can contain unreacted oxethylate. Accordingly, a degree of carboxymethylation can be defined. The formula

therefore denotes a mixture with different amounts of unreacted oxyethylate, provided that the degree of carboxymethylation is between 40 and 100%, preferably between 50 and 100%.

Mixtures with a degree of carboxymethylation between 85 and 100% are particularly effective. Such mixtures accordingly consist of anionic and nonionic surfactant and are considered as carboxymethylated oxethylates according to the invention.

The mixtures of anionic and nonionic surfactant described or the purely anionic compounds (emulsifier) are soluble or at least easily dispersible in conventional reservoir waters.

In preliminary tests, the emulsifier to be used can be optimally adjusted to the existing heavy oil-water system according to its chemical structure.

The surfactants (emulsifiers) of a homologous series (cf.Table A) are dissolved in the water in question and mixed with the heavy oil in question and, after briefly stirring with a paddle stirrer without using high shear forces, they are tested for their emulsifying action and the stability of the emulsion is determined. This assessment of the emulsion is repeated about 24 hours later and then the viscosity is measured as a function of the shear rate, if necessary. Since heavy oil emulsions are somewhat structurally viscous, a range between 10 and 100 sec- ^{1 is} selected for the shear rate, which corresponds approximately to the transport through pipelines. A surfactant is an optimal emulsifier if the amount necessary for emulsification is as small as possible.

The amount is generally from 0.01 to 0.5, in particular from 0.03 to 0.2,% by weight, based on the amount of oil, which corresponds to 100 to 5,000, preferably 300 to 2,000 ppm. For heavy oil liquefaction, the emulsifier is metered in either as a melt or as an aqueous solution or as a dispersion of the oil-water mixture, or else it is added to the water, which is then mixed with the oil. Water here is understood to mean either a more or less saline water that is produced together with the heavy oil, or it can be a cheaply available surface water or, finally, a mixture of both waters. Since heavy oil fields are often exploited by steam flooding, the salinity of the water produced can fluctuate somewhat, which is not critical for the claimed process.

Instead of dosing the emulsifier into the water, it can also be added to the heavy oil itself, especially since the surfactant class claimed here shows good oil solubility. It may be advantageous to use a small amount of a light hydrocarbon mixture as a solubilizer. The mixing of the three components to form the emulsion, namely oil, water and emulsifier, can take place either directly at the borehole or in or near a collection tank or at any other point in the piping system. The mixture ratio of oil to water can vary within wide limits between 10:90 and 90:10. For economic reasons, high oil contents should be aimed at, although it must be taken into account that very high oil contents usually also lead to relatively highly viscous oil-water emulsions. Depending on the system, the economic optimum is between 70 and 85% oil. As is known, the emulsification is favored by mixing devices such as agitators, centrifugal pumps, static mixers, etc., which are used when necessary. The emulsion formed in this way is conveyed through the pipeline system, which can contain intermediate stations and intermediate storage containers. At the pipeline end point, the emulsion is split in a separator, and it may be advantageous to add one or more desmulsifiers. The crude oil dewatered in this way is drawn off and then either to the refinery or a possible further transport, e.g. B. supplied by ship.

Examples

In a glass vessel or polyethylene beaker with a volume of approx. 200 ml, 75 g of Boskan oil (approx. 10 ° API, viscosity at 20 ° C approx. 180 000 mPa - s) and each 25 g of the aqueous surfactant solution mentioned, which also contains neutral electrolyte contains, stirred at room temperature with a simple paddle stirrer (approx. 100 revolutions per minute). If the added surfactant is effective and its amount is sufficient, a uniform-looking emulsion has been created. The mixture is then left to stand at room temperature for about 24 hours and the uniformity of the mixture is examined again, with stirring if necessary using a glass rod. If a smooth, uniform emulsion has formed, the viscosity is measured, as already described. The minimum emulsifier concentration (percent by weight, based on the amount of oil) of the surfactant in question is registered, which is necessary to produce an approximately stable emulsion. "Somewhat stable means that even slight stirring with the glass rod is sufficient to restore the original uniformity, if it has been lost at all.

The examples summarized in the following tables demonstrate the generally high effectiveness of the carboxymethylated oxethylates as heavy oil emulsifiers.

As shown in Table A using the example of lower saline water (1,500 ppm NaCl), the effectiveness of the surfactant can be optimized by varying the chemical structure (changing the degree of EO). Carboxymethylated nonylphenoloxyethylates with an EO degree of approx. 3.3 have the highest effectiveness here. The viscosity is approx. 100 mPa - s at 20 ° C - 100 mPa - s at 37.7 ° C are required - very low.

In Table B, the effect of the same surfactants in the presence of highly saline water (50,000 ppm NaCl) is examined. The EO grade of the most effective surfactants is between 5.5 and 6.0. The significantly increased effectiveness compared to the lower salinar conditions in Table A is surprising

As shown in Table C compared to Table B, the degree of EO of the most effective carboxymethylated oxethylates changes when the nonylphenol residue is replaced by dodecylphenol.

As Table D demonstrates in comparison to Table A, the substitution of the cation (hydrogen instead of sodium) also has a strong influence on the emulsifying properties of the surfactant, the structural variable here again being the EO degree. For the optimal surfactant, it is much higher here, although the reduction in the salinity of the aqueous phase should actually also result in a reduction in the degree of EO.

Table E shows the dependence of the emulsifying activity in the case of a carboxymethylated nonylphenol oxethylate on the degree of carboxymethylation. The influence of alkaline earth ions is also examined. The effectiveness increases with increasing degree of carboxymethylation. This also applies in the presence of alkaline earth metal ions, which moreover weaken the emulsifying effect more than given additional alkaline halides in the same concentration given a high basic salinity.

Since heavy oil is often extracted using steam and hot water flooding, variable salinity must be expected. A corresponding series of dilutions of the salinity is shown in Table F. It is shown that the carboxymethylated oxethylate tested here, in very low concentrations, is an effective emulsifier over a wide salinity range of 10.2 to 1.2%, which leads to highly fluid emulsions.

It is known that heavy oils differ greatly in their composition. For this reason, tests were carried out with another heavy oil in analogy to Table C. This has a density of 12 ° API and contains 30% aromatic, 20% napthenic and 50% paraffinic hydrocarbons. The viscosity at 20 ° C is 70,000 mPa - s. As Table G shows, lightly liquid oil-in-water emulsions can be prepared with small additions of carboxymethylated oxethylates. The EO degree of the carboxymethylated nonylphenols, which lead to a minimum of the necessary surfactant concentration, is significantly higher than that of the heavy oil examined in Table C.

Claims (4)

1. Process for the transportation of viscous crude oils through a pipeline, in which an oil-in-water emulsion, which comprises crude oil and 10 % of water containing an emulsifier, is prepared, transported through the pipeline and subsequently reseparated into crude oil and water, characterized in that the emulsifier employed is carboxymethylated ethoxylate of the formula

where R represents a linear or branched aliphatic radical having 6 to 20 C atoms, or an alkyl- or dialkyl- aromatic radical having 5 to 16 C atoms per alkyl group, where n represents 1 to 40 and M an alkali metal ion or alkaline earth metal ion or ammonium.

2. Process according to claim 1, characterized in that the degree of carboxymethylation of the carboxymethylated ethoxylate is 50 to 100 %.

3. Process according to claim 1, characterized in that the degree of carboxymethylation of the carboxymethylated ethoxylate is 85 to 100 %.

4. Process according to claims 1 to 3, characterized in that the emulsifier concentration, relative to the quantity of oil, is 0.01 to 0.5 per cent by weight (100 to 5,000 ppm).