Earth boring – well treating – and oil field chemistry – Preventing contaminant deposits in petroleum oil conduits
Reexamination Certificate
1998-11-23
2001-06-05
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Preventing contaminant deposits in petroleum oil conduits
C507S261000, C507S266000, C507S267000, C134S040000, C510S188000, C252S364000
Reexamination Certificate
active
06242388
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a mutual solvent capable of forming emulsions with aqueous acid and acid-salt brine solutions. The emulsions are stable, non-toxic, and effectively remove paraffinic and asphaltenic hydrocarbons from equipment used in oil and gas well operations.
BACKGROUND OF THE INVENTION
Oil and gas wells produce crude oils containing substantial amounts of asphaltenic and/or paraffinic hydrocarbons that accumulate on the walls, casing, tubing, etc. of wells and drilling equipment. In addition, deposits of acid-soluble material, such as calcium carbonate or clays, clog the wells and related equipment and slow down production. These deposits can become coated with the asphaltenic and/or paraffinic hydrocarbons. Accordingly, effective clean up requires a solvent that will strip off the hydrocarbons and thereby allow the deposits to break loose and move out of the well. Various techniques have been employed for the removal of deposits including the use of a mutual solvent in combination with an aqueous acidic solution. The mutual solvent is used to remove the asphaltenic and/or paraffinic hydrocarbons while the acid solution removes the acid soluble material. For example, a process wherein a mixture of an octanol and a lower alcohol is used with, ahead of or behind aqueous acid solutions to acidize oil wells is taught by U.S. Pat. No. 3,819,520. The alcohols taught by this patent, however, are not very good at dissolving or stripping asphaltenic hydrocarbons.
A solvent system for use in oil and gas wells which readily strips or dissolves asphaltenes is described by U.S. Pat. No. 5,152,907. The solvent system comprises a hydrocarbon solvent, a substantially water-soluble alcohol, and a substantially oil-soluble alcohol. However, due to growing health and safety concerns there remains a need for a system that readily dissolves or strips paraffins and asphaltenes and which avoids the use of hydrocarbons. The present invention answers this need.
SUMMARY OF THE INVENTION
It has been discovered that 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and/or 2,2,4-trimethyl-1,3-pentanediol diisobutyrate isobutyrate can be used as a principal solvent in combination with a coupling solvent and an acid stable surfactant to form a mutual solvent for use in oil and gas well operations. Accordingly, the invention relates to a mutual solvent for use in oil and gas well operations comprising at least one principal solvent selected from 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, at least one coupling solvent, and an acid stable surfactant. The coupling solvent is selected from ethylene glycol monobutyl ether; diethylene glycol monobutyl ether; propylene glycol monomethyl ether acetate; propylene glycol monomethyl ether, a C
1
-C
5
alkyl alcohol, and mixtures thereof.
It has also been discovered that a mutual solvent according to the invention is capable of forming a stable emulsion when mixed with an aqueous acid or acid-salt brine solution. Accordingly, in another embodiment, the invention relates to an emulsion for use in oil and gas well operations comprising an aqueous acid or acid-salt brine solution and the mutual solvent as described above. An emulsion according to the invention is stable, non-toxic, non-foaming, and effectively removes asphaltenic and paraffinic hydrocarbons from drilling equipment and oil and gas wells. Accordingly, in another embodiment, the invention relates to a method for removing paraffinic and asphaltenic hydrocarbons from drilling equipment and oil and gas wells comprising the step of contacting the equipment or well with a stable emulsion according to the invention.
Additional objects and advantages of the invention are discussed in the Detailed Description which follows, and will be obvious from that description, or may be learned by practice of the invention. It is to be understood that both this summary and the following detailed description are exemplary and explanatory only and are not intended to restrict the invention.
DETAILED DESCRIPTION
The invention relates to a mutual solvent for use in oil and gas well operations comprising at least one principal solvent; at least one coupling solvent; and at least one acid stable surfactant. The principal solvent is selected from 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate and mixtures thereof. 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate are commercially available from Eastman Chemical Company, Kingsport, Tenn. and sold under the names TEXANOL® and TXIB® respectively. In another embodiment, the principal solvent may be an off stream product of TEXANOL®, such as, for example, solvent MTE (modified) available from Eastman Chemical Co., Texas Eastman Division, Longview, Tex. Solvent MTE comprises the following mixture of solvents:
Approximate
Components
Weight %
2,2,4-trimethyl-1,3-pentanediol diisobutyrate
5-60
2,2,4-trimethyl-1,3-pentanediol monoisobutyrate
20-50
high boilers
5-25
3-keto-2,2,4-trimethylpentyl isobutyrate
5-20
mid boilers
5-20
2,2-dimethyl-1,3-propanediol diisobutyrate
5-15
2,2,4-trimethyl-1,3-pentanediol
1-10
3-isobutoxy-2,2,4-trimethylpentanol
0-5
Preferably, the principal solvent is present in the mutual solvent according to the invention at from about 5 to about 60% by weight, preferably from about 10 to about 50% by weight, more preferably from about 15 to about 35% by weight, and most preferably from about 25 to about 30% by weight based on the mutual solvent.
The coupling solvent used in a mutual solvent of the invention is preferably selected from ethylene glycol monobutyl ether; diethylene glycol monobutyl ether; propylene glycol monomethyl ether acetate; propylene glycol monomethyl ether; and a C
1
-C
5
alkyl alcohol, such as, for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and pentanol. The coupling solvent is present in a mutual solvent according to the invention in an amount sufficient to form a stable emulsion of the principal solvent in an acid or acid/salt brine solution. Preferably, the coupling solvent is present in an amount ranging from about 1 to about 70%, more preferably about 10 to about 50%, most preferably from 15 to about 45% by weight based on the mutual solvent.
A mutual solvent according to the invention additionally comprises an acid stable surfactant to increase the stability of the mutual solvent-acid or acid/salt brine solution emulsion. In the context of the invention “acid stable surfactant” refers to a surfactant that is stable at acidic pH, preferably at a pH equal to or less than about 4. Any of the surfactants normally employed in well acidizing may be used. Preferably, the surfactant is an anionic or nonionic surfactant. Preferred anionic surfactants include alkyl phosphate esters, such as C
8
-C
20
aliphatic or aromatic straight or branched chain phosphate esters. Suitable alkyl phosphate esters useful as the acid stable surfactant in a mutual solvent according to the invention include STRODEX PSK-28, STRODEX P-100, and STRODEX PK-90, available from Dexter Chemical Corp., TANATERGE PE-37 and TANATERGE PE-67 available from Sybron Chemicals Inc. (previously Dexter Chemical Corp.), and RHODAFAC PL-620, RHODAFAC PE-510, RHODAFAC RE-410, RHODAFAC RE-610, RHODAFAC RE-960, RHODAFAC DX-660, RHODAFAC RS-410, RHODAFAC RS-610, and RHODAFAC RS-710 available from Rhone Poulenc. Suitable nonionic acid stable surfactants include oxyalkylated alcohols, oxyalkylated phenols, and oxyalkylated polyols having an HLB ranging from about 2 to about 10.
The acid stable surfactant is present in an amount sufficient to stabilize an emulsion of the principal solvent in an acid or acid/salt brine solution, preferably the acid stable surfactant is present at from about 1% to about 40%, more preferably from about 10% to about 30%, most preferably from about 15% to about 25% by weight based on the mutual solvent.
In a particularly preferred embodiment, a mutu
Goodwin Melissa Darlene
Sharma Mahendra Kumar
Smith Ronald Allen
Eastman Chemical Company
Gwinnell Harry J.
Smith Matthew W.
Tucker Philip
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