Cleaning and liquid contact with solids – Processes – Oils – grease – tar – or wax removal – by dissolving
Reexamination Certificate
1999-11-26
2002-04-09
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Oils, grease, tar, or wax removal, by dissolving
C134S022100, C134S022110, C134S022140, C134S022190, C510S188000, C166S304000, C166S311000
Reexamination Certificate
active
06368422
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process and compositions for removing solid asphaltene residues from the surface of production equipment or the formation surrounding the well in the production and processing of petroleum and to the use of certain fatty acid esters for this purpose.
BACKGROUND OF THE INVENTION
Crude oil is a complex mixture of various paraffinic and aromatic hydrocarbons, the individual constituents having very different chemical and physical properties. Accordingly, both readily volatile low-viscosity constituents and wax-like high-viscosity fractions are obtained in the distillation of crude oil. The wax-like fractions include petroleum resins and, for the most part, asphaltenes which are colloidally dispersed in the oil phase.
Asphaltenes consist of a mixture of various saturated, unsaturated and aromatic hydrocarbons, more especially naphthalene derivatives. They also contain heterocyclic hydrocarbons which partly contain complexed metal ions also. Asphaltenes are also rich in sulfur, nitrogen and oxygen compounds. In view of their complex composition, asphaltenes are generally characterized by their solubility. Thus, the petroleum fraction insoluble in heptane or pentane but soluble in toluene is referred to by the name of asphaltenes, the “dissolution” of the asphaltenes representing a complex process of which there has hitherto been no complete theoretical description (cf. E. Y. Sheu, O. C. Mullins,
Asphaltenes—Fundamentals and Applications,
Plenum Press, New York, 1995, Chapter I and Chapter III).
Asphaltenes are present in the oil phase of crude oil as micellar colloids, the individual micelles consisting of several different molecules. The micelles differ in size according to the temperature and composition of the oil phase. For example, it is known that lighter aromatic hydrocarbons in crude oil stabilize the asphaltene micelles. Under the conditions under which petroleum is produced, however, the asphaltenes are often precipitated which results in the formation of highly viscous, wax-like to solid residues on the surface of the production equipment and the oil-containing formation surrounding the well. The asphaltene residues block the pores of the formation which results in a considerable reduction in the production rates and, in the worst case, can even make production completely impossible. Asphaltene residues on the surfaces of production equipment, for example the delivery tube or the casing walls of pipelines or separators, can also seriously affect production.
Accordingly, there are various known methods for removing asphaltene residues occurring in the production of petroleum. For example, the residues can be removed mechanically or by treatment with hot mineral oil or with aqueous surfactant solutions. In general, however, efforts are made to remove the residues with suitable organic solvents, more especially benzene, toluene or xylene. However, since some of these compounds do not have adequate dissolving properties, a search was made for alternatives. According to the teaching of U.S. Pat. No. 5,504,063, for example, the dissolving properties of the above-mentioned aromatic hydrocarbons can be improved by addition of up to 50% by volume of certain N-substituted imidazolines or condensation products of polyamines with fatty acids. By contrast, U.S. Pat. No. 5,382,728 proposes a special mixture of saturated, aromatic and polyaromatic hydrocarbons as suitable solvents for asphaltene residues.
However, these solvents or solvent mixtures cannot be used in every case in view of their low flash points, their high volatility and their high cost. In addition, because working materials are having to meet more stringent environmental compatibility requirements and with industrial safety in mind, efforts are being made to avoid the use of ecologically unsafe and carcinogenic substances.
DESCRIPTION OF THE INVENTION
Accordingly, the problem addressed by the present invention was to find ecologically safe alternatives to the solvents known from the prior art for the solid asphaltene residues which occur in the production and processing of petroleum.
Although it was already known that asphaltenes can be precipitated with polar liquids, such as alcohols or esters (H.-J. Neuman, I. Rahimian, G. Zenke,
Analytik der Asphaltene, Erdöl und Kohle—Erdgas—Petrochemie,
Vol. 39, No. 2, 1986), it has surprisingly been found that certain fatty acid esters are suitable as solvents for asphaltene residues.
In a first embodiment, therefore, the present invention relates to the use of fatty acid esters corresponding to general formula (I):
R
1
—COO—(C
n
H
2n
O)
x
—R
2
(I)
In which R
1
is an alkyl group containing 6 to 22 carbon atoms or a (CH
2
)
m
—COOR
4
group, R
2
and R
4
independently of one another representing an alkyl group containing 1 to 8 carbon atoms, n is the number 2 or 3 and m is a number of 1 to 6 and x is 0 or a number of 1 to 12, for removing solid asphaltene residues from the surfaces of production equipment or the petroleum-containing formation surrounding the well in the production and processing of petroleum.
Asphaltenes in the context of the present invention are understood to be those constituents of crude oil which, according to DIN 51595 (December 1983), precipitate when the petroleum is dissolved in 30 times the volume of heptane at 18 to 28° C. and which are soluble in benzene. Solid asphaltene residues are residues which have a solid or wax-like consistency at the particular working temperature to which the surface is exposed and of which more than 50% by weight consist of asphaltenes. Besides asphaltenes, the solid residues may also contain petroleum resins or other solids.
The solid asphaltene residues can form on the surface of production equipment in the production of petroleum, production equipment in the context of the invention being understood to include any equipment which comes into direct contact with the oil. Such equipment includes, for example, the production tube, the casing of the well and all other oil-carrying lines, pipelines, separators, pumps and valves. Except for the casing, the surface of such production equipment normally consists of metal, more especially steel, the casing generally consisting of concrete. However, production equipment in the context of the invention also includes the crude oil processing steps which follow the actual production cycle, for example the distillation of the crude oil fractions. Asphaltene residues can also occur in the transportation of crude oil through pipelines or during storage thereof and can thus affect production.
However, solid asphaltene residues are also formed on the surface of the petroleum-containing formation surrounding the well where they block the pores of the rock which leads to a considerable reduction in the production rate.
The fatty acid esters which are used in accordance with the invention to remove the solid asphaltene residues may be synthesized by any methods known to the expert. To this end, alcohol and fatty acid are normally reacted in the presence of acidic or basic catalysts, optionally under pressure. Another method of obtaining fatty acid esters corresponding to general formula (I) is the transesterification of natural fats and oils with methanol in the presence of a catalyst. Suitable natural oils are, for example, rapeseed oil, sunflower oil, soybean oil, linseed oil or coconut oil.
Suitable alcohols which may be used in the synthesis of the esters used in accordance with the invention are either unbranched, such as methanol, ethanol, propanol, butanol, pentanol, hexanol, or branched, such as isopropanol, isobutanol, 2-methyl or 2-ethyl hexanol.
Suitable saturated fatty acids are caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid or behenic acid. Unsaturated fatty acids are, for example, lauroleic acid, palmitoleic acid, oleic acid, ricinoleic acid, linoleic acid and linolenic acid. Besides the monocarboxylic acids, esters of dicarboxylic acids, such as maleic, suc
Breuer Wolfgang
Herold Claus-Peter
Drach John E.
Gulakowski Randy
Henkel Kommanditgesellschaft auf Aktien
Millson, Jr. Henry E.
Smetana Jiri
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