Wells – Processes – Chemical inter-reaction of two or more introduced materials
Reexamination Certificate
2000-03-07
2001-11-13
Suchfield, George (Department: 3672)
Wells
Processes
Chemical inter-reaction of two or more introduced materials
C166S307000, C166S902000, C507S244000, C507S266000, C507S267000, C507S277000, C507S934000, C507S939000
Reexamination Certificate
active
06315045
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to methods and aqueous acid compositions for reducing metal surface corrosion and the precipitation of metal sulfides from the aqueous acid compositions when acidizing a sour well or other similar location.
2. Description of the Prior Art.
Aqueous acid solutions are commonly used to treat oil or gas wells. For example, subterranean well formations are often contacted with aqueous acid solutions to increase the permeabilities of the formations whereby the production of oil and/or gas therefrom is increased. Aqueous acid solutions are also utilized to etch flow channels in the faces of fractures formed in the formations and to clean out perforations and tubular goods in wells.
When the well being treated is sour, i.e., the fluids produced contain a significant quantity of sulfide compounds, and particularly hydrogen sulfide, problems are often encountered as a result of the precipitation of metal sulfide such as iron sulfide from the aqueous acid solution. That is, dissolved sulfide ions and dissolved ferrous ions from ferrous sulfide scale and/or metal ions from the subterranean formation being treated react to form metal sulfides in the acid solution. The metal sulfides precipitate from the acid solution when the pH reaches a level greater than about 1.9. The pH of spent aqueous acid solutions used to treat subterranean formations is greater than 1.9, and therefore, metal sulfides dissolved in an unspent acid solution precipitate at some point before becoming spent. The metal sulfide precipitates can plug the treated formation and cause serious damage to the well.
Aqueous acid solutions are also used to remove scale from tubular apparatus such as heat exchangers, boilers and the like. If the scale contains metal and sulfide compounds, metal sulfide precipitates can form which interfere with the cleaning process.
While a variety of methods and compositions have been developed heretofore for preventing the precipitation of metal sulfides from aqueous acid treating solutions, there is a continuing need for improved acidizing methods and compositions which are relatively inexpensive and produce little or no metal sulfide precipitates.
SUMMARY OF THE INVENTION
The present invention provides methods and aqueous acid compositions for treating subterranean formations in sour wells, tubular apparatus and the like wherein corrosion of metal surfaces contacted by the aqueous acid compositions and metal sulfide precipitation from the aqueous acid compositions are reduced or prevented.
The methods of the present invention for acidizing a sour well containing metal compounds and sulfide compounds are basically comprised of combining an aldol-amine adduct with an aqueous acid solution to preferentially react with sulfide ions subsequently dissolved by the aqueous acid solution and thereby prevent subsequently dissolved metal ions from reacting with the sulfide ions and precipitating. Thereafter, the aqueous acid solution containing the aldol-amine adduct is introduced into the well.
The aqueous acid compositions of the invention are basically comprised of water, an acid selected from the group consisting of inorganic acids, organic acids and mixtures thereof and an aldol-amine adduct which is soluble and stable in the water and acid. The aldol-amine adduct preferentially reacts with sulfide ions when they are dissolved in the acid compositions thereby preventing the dissolved sulfide ions from reacting with dissolved metal ions and precipitating.
It is, therefore, a general object of the present invention to provide improved methods and compositions for reducing metal corrosion and metal sulfide precipitation when acidizing sour wells and the like.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention provides methods and aqueous acid compositions for reducing metal surface corrosion and metal sulfide precipitation when acidizing a well or apparatus containing metal compounds and sulfide compounds.
The term “sour well” is used herein to mean oil, gas and other wells containing metal compounds and sulfide compounds, particularly hydrogen sulfide. When such wells are treated with an aqueous acid solution to stimulate the production of hydrocarbons therefrom, the aqueous acid solution dissolves sulfide ions and metal ions such as iron, zinc and lead. When the pH of the aqueous acid solution reaches a level of about 1.9 and higher, the metal ions and sulfide ions react and metal sulfides precipitate from the solution. Metal sulfide precipitate can plug the acidized formation or otherwise cause serious damage to wells and associated production equipment.
In accordance with the methods of the present invention, an aldol-amine adduct is combined with an aqueous acid solution in an amount whereby when the acid solution contains dissolved sulfide ions and dissolved metal ions, the sulfide ions are prevented from reacting with the metal ions. That is, the aldol-amine adduct preferentially reacts with sulfide ions in the aqueous acid solution and thereby prevents the sulfide ions from reacting with metal ions therein.
Aldol (CH
3
CH(OH)CH
2
CHO) has heretofore been utilized as a hydrogen sulfide scavenger which prevents metal sulfide precipitation from aqueous acid solutions. However, when aldol or an aqueous solution of aldol is stored, it quickly separates into two layers with all of the aldol concentrated in the bottom layer. The bottom layer containing the aldol is not redispersible in the top layer or in water or acid. Also, the aldol in the bottom layer has very little activity as a sulfide scavenger. Thus, the use of aldol as a hydrogen sulfide scavenger in aqueous acid solutions can result in less than satisfactory results.
In accordance with the present invention aldol is reacted with an amine to form an aldol-amine adduct. The aldol can be from any source including the aldol layer which has separated as a result of storage.
The amine utilized to prepare the aldol-amine adduct must be a primary amine which contains a hydroxyl function within three carbon atoms from the amine group. Examples of such amines include, but are not limited to, monoethanolamine (HOCH
2
CH
2
NH
2
), 3-amino-1-propanol (H
2
NCH
2
CH
2
CH
2
OH), 3-amino-1,2,-propanediol (H
2
NCH
2
CH(OH)CH
2
OH) and tris(2-hydroxyethyl)methylamine (tris(HOCH
2
CH
2
)
3
CNH
2
). Of these, monoethanolamine is presently preferred.
Amines which do not react with aldol to form an aldol-amine adduct that functions as a sulfide scavenger include secondary amines, hydroxylamine and amines without the hydroxyl group.
The aldol is reacted with the amine, e.g., monoethanolamine, in a molar ratio of aldol to monoethanolamine in the range of from about 1:1 to about 1:0.7 whereby an aldol-monoethanolamine adduct is formed. The resulting adduct is soluble and stable in aqueous acid solutions. Further, the adduct can be stored for very long periods of time without separation.
The aldol-amine adduct can be utilized as a hydrogen sulfide scavenging additive in various aqueous acid solutions containing inorganic acids, organic acids or mixtures of such acids. Examples of inorganic acids with which the additive can be used include hydrochloric acid, hydrofluoric acid and fluoboric acid. Examples of organic acids are formic acid, acetic acid, citric acid, lactic acid, thioglycolic acid and glycolic acid. Generally, the acid solutions utilized for scale removal or stimulating the production of oil and/or gas from subterranean well formations are aqueous acid solutions of predominantly inorganic acids. That is, the aqueous acid solutions contain inorganic acid in an amount in the range of from about 5% to about 30% by weight of the acid solutions.
The aldol-amine adduct is preferably admixed with an aqueous acid solution prior to when the aqueous acid solution dissolves
Dougherty, III Clifford C.
Halliburton Energy Service,s Inc.
Kent Robert A.
Suchfield George
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