CA1060640A - Methods and compositions for treating low temperature subterranean well formations - Google Patents
Methods and compositions for treating low temperature subterranean well formationsInfo
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- CA1060640A CA1060640A CA210,087A CA210087A CA1060640A CA 1060640 A CA1060640 A CA 1060640A CA 210087 A CA210087 A CA 210087A CA 1060640 A CA1060640 A CA 1060640A
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Abstract
Abstract of the Disclosure The present invention relates to methods of treating low temperature subterranean forma-tions using novel gelled aqueous compositions wherein the treating composition is introduced into the formation and maintained therein until the composition reverts to a thin fluid. The composition comprises an aqueous liquid, a water soluble organic gelling agent, a free radical generating agent, and a reducing agent.
Description
1060~4~
Gelled aqueous fluids have been developed and used extensively in the treatment of subterranean formations.
For example, such fluids are commonly utilized as frac-turing fluids for creating fractures in formations and for placing particulated solid propping agent therein. Following such treatments, the gelled fluid is caused to break or revert to a thin fluid so that it can either be pumped or produced back from the treated formation.
The breaking of aqueous gelled treating fluids has heretofore been accomplised using a variety of techniques such as by the degradative action of acids, enzymes or mild oxidizing agents. However, the use of prior gelled compositions and techniques for causing the compositions to revert to thin fluids has been limited to oper..ting temperatures greater than about 120 F. That is, the use of gelled aqueous solutions in subterranean well forma-tions existing at temperatures below about 120 F has heretofore been severely restricted due to the lack of effective techniques or breaking such gels at temperatures ~ -below about 120F.
By the present invention gelled aqueous compositions and methods of using such compositions for treating sub-terranean formations below 120F are provided. The gelled compositions of this invention readily break or revert to thin fluids at temperatures as low as 70F and are particularly suitable as treating fluids for fracturing and propping low temperature formations. -
Gelled aqueous fluids have been developed and used extensively in the treatment of subterranean formations.
For example, such fluids are commonly utilized as frac-turing fluids for creating fractures in formations and for placing particulated solid propping agent therein. Following such treatments, the gelled fluid is caused to break or revert to a thin fluid so that it can either be pumped or produced back from the treated formation.
The breaking of aqueous gelled treating fluids has heretofore been accomplised using a variety of techniques such as by the degradative action of acids, enzymes or mild oxidizing agents. However, the use of prior gelled compositions and techniques for causing the compositions to revert to thin fluids has been limited to oper..ting temperatures greater than about 120 F. That is, the use of gelled aqueous solutions in subterranean well forma-tions existing at temperatures below about 120 F has heretofore been severely restricted due to the lack of effective techniques or breaking such gels at temperatures ~ -below about 120F.
By the present invention gelled aqueous compositions and methods of using such compositions for treating sub-terranean formations below 120F are provided. The gelled compositions of this invention readily break or revert to thin fluids at temperatures as low as 70F and are particularly suitable as treating fluids for fracturing and propping low temperature formations. -
-2-.. .. . . . . . .
10~0640 Broadly described, the novel gelled aqueous composi-tions of the present invention are comprised of an aqueous liquid, a water soluble organic gelling agent, a water soluble free radical generating agent for generating free radicals to degrade the gelling agent, and a water soluble reducing agent for accel-erating the generation of free radicals at low temperatures.
The invention relates to an aqueous composition for treating subterranean formations having temperatures of up to about 120 F comprising: an aqueous liquid, a water soluble organic gelling agent present in said aqueous liquid in an amount of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid sufficient to increase the viscosity thereof, a water soluble oxidizing agent having the property of generating free radicals, and a water soluble :
reducing agent to accelerate the generation of said free :-radicals: wherein said reducing agent is a water soluble metal salt, selected from the group consisting of cuprous, ferrous, stannous, cobaltous, chromous", nickelous, titanous, manganous :~
and arsenous salts of the halides, sulfates and nitrates and mixtures thereof,, and said reducing agent is present in said composition in an amount in the range of from about O.l~to about 7.5 parts by weight per 100 parts by weight aqueous liquid; and wherein said oxidizing agent is selected from the group consist-ing of water soluble peroxide compounds, water soluble persulfate compounds and mixtures thereof and said oxidizing agent is present in an amount of about 0.0001 to about 2 parts by weight free radical generating agent per 100 parts by weight aqueous liquid; and further wherein said organic gelling ag~t is selected from the group consisting of sodium polyacrylate, polyacrylic acid, polysodium-2-acrylamide-3-propylsulfonate, polyacrylamides and polymethacrylamides hydrolyzed to convert from 0 o about 70 percent of amide groups to carboxyl groups which are then '~ -3 ~ .
., ,,.. ~
,.. . : ~, ,. ~ . . .. . . .
~06069t0 neutralized with ammonium or an alkali metal hydro~ide, guar gum, locust bean gum, gum tragacanth, hydroxyethyl guar gum, hydroxy-propyl guar gum, carboxymethyl guar gum and mixtures thereof.
Suitable aqueous liquids are the aqueous liquids commonly used for treating subterranean formations. of these aqueous liquids, potable water is preferred because it does not contain dissolved salts which can interfere with the formation of viscous gels with water soluble organic gelling agents.
However, brine produced from subterranean formations and sea water are often available for treating subterranean formations and form viscous gels with water soluble organic gelling agents.
It has also been found desirable to include certain salts such as potassium and sodium chloride in the gelled aqueous compo-sitions to prevent the composition from swelling clay or damaging shale contained in subterranean formations. In other gelled aqueous compositions it has been found desirable to mix the aqueous liquid with lower alkyl alcohols such as methanol, ethanol or isopropanol. The use of salts and alcohol, as well as other additives for the gelled aqueous composition, are often desirable and are useful when they do not interfere with the formation of viscous gels when water soluble organic gelling agents are mixed with aqueous liquids containing these materials.
:
- 3a -1016~640 Water soluble organic gelling agents which readily form viscous gels with aqueous liquids and which are suitable for use in accordance with the present invention are water soluble synthetic polymers, water soluble derivatives of cellulose, water soluble polysaccharides, water soluble deriva-tives of polysaccharide, and mixtures of the foregoing compounds.
Examples of suitable water soluble synthetic polymers include, but are not limited to, polymethacrylamide, polyacryl-a~ide, sodium polyacrylate, polyacrylic acid and polysodium-2-acrylamide-3-propylsulfonate. Particularly preferred such polymers are polyacrylamides and polymethacrylamides which have been hydrolyzed such that from about O to about 70 per-cent of the amide groups have been converted to carboxyl groups and then neutralized with ammonium or an alkali metal hydroxide.
The most preferred water soluble synthetic polymer for use as a gelling agent in accordance with the present invention is a polyacrylamide polymer which has been hydrolyzed such that about O to 30 percent of the amide groups have been converted to car-boxyl groups and the carboxyl groups neutralized with an alkali ~0 metal or ammonium hydroxide.
Water soluble derivative~ of cellulose suitable for use as gelling agents in accordance with the present inven-tion include, but are not limited to, hydroxyethylcellulose, carboxymethylhydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, propylcellulose and sulfo-propylcellulose. Of these, hydroxyethylcellulose and carboxy-methylhydroxyethylcellulose are preferred.
..
.
Suitable water soluble polysaccharides are guar gum, locust bean gum, and gum tragacanth. Water soluble deriva-tives of the ~oregoing polysaccharide compounds can also be utilized as gelling agents, e.g., hydroxyethyl guar gum, hydroxypropyl guar gum and carboxymethyl guar gum. Of the various polysaccharides which can be used, guar gum i9 pre-ferred.
The preferred gelling agents mentioned above, i.e., polyacrylamide polymers which have been hydrolyzed and neutral-ized, hydroxyethylcellulose, carboxymethylhydroxyethylcellu-lose and guar gum are readily commercially available and form stable gels of desired viscosity when added to aqueous liquids at relatively low concentrations.
Gelling agent concentrations of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid are generally required. At concentrations below about 0.1 part hy weight gelling agent per 100 parts by weight aqueou~ liquid, the resulting gel does not have sufficient viscosity to achieve desired objectives, e.g., to adequately maintain propping agents in suspension. At concentrations above about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid, the resulti~g com-position is generally of such a high viscoty that excessive ~ -friction losses are encountered when displacing the composi-tion through a conduit at high velocities. When using the preferred gelling agents mentioned above, they ~0~0~40 are preferably added to the aqueous liquid in an amount of about 0.25 to about 1.5 parts by weight gelling agent per 100 parts by weight aqueous liquid.
The free radical generating agents useful in accordance with the present invention are water soluble oxidizing agents having the property of generating free radicals for degrading ~ -the gelling agent. Such oxidizing agents include water soluble perixide compounds, persulfate compounds, or mixtures thereof. Examples of preferred and particularly suitable water soluble peroxide compounds include, but are not limited to, hydrogen peroxide, tertiary butyl hydroperoxide and di-tertiary butyl peroxide. Preferred water soluble persulfates include ammonium persulfate and the alkali metal persulfates.
The foregoing free radical generating agents are utilized in the compositions of the present invention in an amount of about 0.0001 to about 2 parts by weight free radical generator per 100 parts by weight aqueous liquid.
At a concentration below about 0.0001 part free radical generator per 100 parts aqueous liquid, the rate of degra-dation of the gelling agent is low and the time required for breaking the gel is generally too long. Above a con-centration of about 2 parts by weight free radical generator per 100 parts by weight aqueous liquid) excess free radicals are generated. When utilizing the preferred free radical generating agents mentioned above, they are combined with the aqueous liquid and gelling agent in an amount of about 0.001 to about 0.75 parts by weight free radical generator per 100 parts by weight aqueous liquid.
10~ 4(~
Reducing agents which are suitable for use in accordance with the present invention and which function to accelerate the generation of free radicals over an extended period of time at low temperatures are water soluble metal salts wherein the oxidation number of the metal ion is less than -the highest possible oxidation number for that ion. Examples of such salts are the cuprous, ferrous, stannous, cobaltous, chromous, nickelous, titanous, manganous and arsenous salts of the halides, sulfates and nitrates. Of these, cuprous chloride, ferrous chloride and cobaltous chloride are preferred in that they have a limited solubility in aqueous fluids, and as a result the aqueous treating compositions of the present invention including these salts remain gelled for periods of time long enough to place and utilize the compositions in subterranean well formations. That is~
the reducing agent dissolves slowly so that the reactivity of the free radical generating agent is not accelerated too quickly. The metal salt used is preferably included in the treating composition in an amount at least equal to the amount required to stoichiometrically react with the free radical generating agent present in the composition. This concentration is generally about 0.1 to about 7.5 parts by weight metal salt per 100 parts by weight aqueous liquid.
While the novel gelled aqueous compositions of the present invention have a variety of uses in treating low temperature subterranean well formations, the compositions ~ -are particularly suitable as fracturing fluids. That is, the gelled aqueous compositions can be formed with a ~ ~
': ' .: ~:: .
10~0640 viscosity sufficient to bring about the fracturing of a well formation using conventional techniques. Further, the gelled aqueous compositions are able to maintain solid particulated propping agents in suspension so that the propping agent can be placed in the fractures thereby preventing them from closing.
In carrying out the methods of the present invention for treating a low temperature subterranean formation penetrated by a well bore, an aqueous ~elled composition of the present in-vention can be prepared on the surface by mixing the gelling agent and the reducing agent with a quantity of aqueous liquid at atmospheric temperatures. The free radical generating agent is then added to the aqueous liquid and the resulting gelled aqueous composition is introduced into the formation, usually by pumping the gelled aqueous composition through a string of pipe disposed in the well bore. Once the treatment of the formation is completed, a sufficient time period is allowed for the gelled aqueous composition to break or revert to a thin fluid. As stated previously, even at well formations existing at temperatures as~low as 70F~-,) only a relatively short period of time is required for the gelled aqueous com-positions to break. Once broken, the aqueous liquid returns to the well bore, along with fluids produced from the subterran- -ean formation.
The invention relates to a method for reducing the viscosity of an aqueous gel, said method consisting essentially of: mixing with said aqueous gel a water soluble oxidizing agent having the property of generating free radicals, and a water soluble reducing agent to accelerate the generation of said free radicals, and subjecting said aqueous gel containing said ox~dizing agent and said reducing agent to temperatures of up to about 120bF for a time sufficient to reduce the viscosity of said aqueous gel;
~ -8-A~. ,.
.,.. ,,, . , . .. , . - ~ .
106C)640 wherein said reducing agent is a water soluble metal salt, selected from the group consisting of cuprous, ferrous, stannous, cobaltous, chromous, nickelous, titanous, manganous and arsenous salts of the halides, sulfates and nitrates and mixtures thereof: and said reducing agent is present in said composition in an amount in the range of from about 0.1 to about 7.5 parts by weight per 100 parts by weight aqueous liquid, and wherein said oxidizing agent is selected from the group consist-ing of water soluble peroxide compounds, water soluble persulfate compounds and mixtures thereof and said oxidizing agent is pre-sent in an amount of about 0.0001 to about 2 parts by weight free radical generating agent per 100 parts by weight aqueous liquid:
and wherein said aqueous gel is comprised of an aqueous liquid and a water soluble organic gelling agent present in an amount of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid sufficient to increase viscosity :
of said aquous gel to a desired level; and further wherein said -:;
organic gelling agent is selected from the group consisting of sodium polyacrylate, polyacrylic acid, polysodium-2-acrylamide-3-propylsulfonate, polyacrylamides and polymethacrylamides hydrolyzed to convert from 0 to about 70 percent of amide groups -to carboxyl groups which are then neutralized with ammonium or an alkali metal hydroxide, guar gum, locust bean gum, gum traga- :
canth, hydroxyethyl guar gum, hydroxypropyl guar gum, carboxy-methyl guar gum and mixtures thereof. :
In fracturing a low temperature subterranean formationaccording to the method of the present invention, a gelled aqueous composition o~ the invention can be - 8a -1~60640 prepared with a quantity of solid particulated propping agent suspended therein. In preparing the composition, the propping agent i9 preferably added to a quantity of aqueous liquid prior to or simultaneously with the gelling agent and reduc-ing aqent and the mixture vigorously agitated to form the gel with propping agent uniformly distributed therein. The free radical generating agent is added to the composition while being agitated, and the composition is then introduced into the formation and forced into fractures created therein BO
that the propping agent is placed in the fractures. After the propping agent has been placed, the composition is allowed to revert to a thin 1uid and recovered leaving the propping agent in the fractures so that they are held open. A~ will be understood by those skilled in the art, the recovery of the treating composition can be accomplished in a variety of way~, but generally simply involves placing the treated well formation on production so that the fluids are produced back-along with natural fluids from the formation.
In order to present a clear understanding of the present invention the following examples are given:
Example 1 A gelled a~ueous composition is prepared in the labor-atory by dissolving a mixture of 4.8 grams (the equivalent of 80 ~ounds per 1000 gallons) of guar gum and 0.3 grams of ferrous sulfate in 500 milliliters of tap water. A highly viscous aqueou~ composition i~ formed at a temperature of 70F. 0.3 1060~40 grams of potassium persulfate are then added to the aqueous composition and the mixt~e is viyorously agitated with the result that the composition reverts to a thin fluid having a viscosity of less than 2 centipoises.
Example 2 A gelled aqueous composition is prepared in the laboratory by dissolving 4.8 grams of hydroxyethylcellulose and 0.3 grams of ferrous sulfate in 500 milliliter.s of tap water.
A highly viscous aqueous composition is formed at a tempera-ture of 70F. 0.3 grams of potassium persulfate are added to the composition and upon vigorous agitation the composi-tion reverts to a thin fluid having a low Vlscosity.
Example 3 A polyacrylamide polymer mixture,hydrolyzed such that from about 0 to about 30 percent of the amide groups are Y
converted to carboxyl groups and then neutralized with sodium hydroxide, is added to 500 milliliters of tap water in an amount of 4.8 grams, along with 0.3 grams of ferrous ~ -sulfate. A gelled aqueous composition at a temperature of 70F is formed. 0O3 grams of potassium persulfate are added to the aqueous composition and after vigorous agi-tation the composition reverts to a thin fluid having a viscosity of less than 2 centipoises.
While the gelled aqueous compositions of the present --invention are particularly suitable for carrying out frac-turing and fracture propping operations in low temperature subterranean well formations, the compositions are not so limited in that they can be utilized for carrying out ' -: . , . . . . ~ . ... .. ; .
~0~;0~i40 numerous other operations. As will be understood by those skilled in the art, many variations, both as to methods of utilizing the compositions and in the relative propor-tions of components of the compositions can be made without departing from the scope of this invention. Furthermore, additional components and/or additives can be incorporated with the compositions to bring about desired properties such as the reduction of fluid loss, etc. The invention should be limited only by the lawful scope of the appended claims.
.. .. . . .
10~0640 Broadly described, the novel gelled aqueous composi-tions of the present invention are comprised of an aqueous liquid, a water soluble organic gelling agent, a water soluble free radical generating agent for generating free radicals to degrade the gelling agent, and a water soluble reducing agent for accel-erating the generation of free radicals at low temperatures.
The invention relates to an aqueous composition for treating subterranean formations having temperatures of up to about 120 F comprising: an aqueous liquid, a water soluble organic gelling agent present in said aqueous liquid in an amount of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid sufficient to increase the viscosity thereof, a water soluble oxidizing agent having the property of generating free radicals, and a water soluble :
reducing agent to accelerate the generation of said free :-radicals: wherein said reducing agent is a water soluble metal salt, selected from the group consisting of cuprous, ferrous, stannous, cobaltous, chromous", nickelous, titanous, manganous :~
and arsenous salts of the halides, sulfates and nitrates and mixtures thereof,, and said reducing agent is present in said composition in an amount in the range of from about O.l~to about 7.5 parts by weight per 100 parts by weight aqueous liquid; and wherein said oxidizing agent is selected from the group consist-ing of water soluble peroxide compounds, water soluble persulfate compounds and mixtures thereof and said oxidizing agent is present in an amount of about 0.0001 to about 2 parts by weight free radical generating agent per 100 parts by weight aqueous liquid; and further wherein said organic gelling ag~t is selected from the group consisting of sodium polyacrylate, polyacrylic acid, polysodium-2-acrylamide-3-propylsulfonate, polyacrylamides and polymethacrylamides hydrolyzed to convert from 0 o about 70 percent of amide groups to carboxyl groups which are then '~ -3 ~ .
., ,,.. ~
,.. . : ~, ,. ~ . . .. . . .
~06069t0 neutralized with ammonium or an alkali metal hydro~ide, guar gum, locust bean gum, gum tragacanth, hydroxyethyl guar gum, hydroxy-propyl guar gum, carboxymethyl guar gum and mixtures thereof.
Suitable aqueous liquids are the aqueous liquids commonly used for treating subterranean formations. of these aqueous liquids, potable water is preferred because it does not contain dissolved salts which can interfere with the formation of viscous gels with water soluble organic gelling agents.
However, brine produced from subterranean formations and sea water are often available for treating subterranean formations and form viscous gels with water soluble organic gelling agents.
It has also been found desirable to include certain salts such as potassium and sodium chloride in the gelled aqueous compo-sitions to prevent the composition from swelling clay or damaging shale contained in subterranean formations. In other gelled aqueous compositions it has been found desirable to mix the aqueous liquid with lower alkyl alcohols such as methanol, ethanol or isopropanol. The use of salts and alcohol, as well as other additives for the gelled aqueous composition, are often desirable and are useful when they do not interfere with the formation of viscous gels when water soluble organic gelling agents are mixed with aqueous liquids containing these materials.
:
- 3a -1016~640 Water soluble organic gelling agents which readily form viscous gels with aqueous liquids and which are suitable for use in accordance with the present invention are water soluble synthetic polymers, water soluble derivatives of cellulose, water soluble polysaccharides, water soluble deriva-tives of polysaccharide, and mixtures of the foregoing compounds.
Examples of suitable water soluble synthetic polymers include, but are not limited to, polymethacrylamide, polyacryl-a~ide, sodium polyacrylate, polyacrylic acid and polysodium-2-acrylamide-3-propylsulfonate. Particularly preferred such polymers are polyacrylamides and polymethacrylamides which have been hydrolyzed such that from about O to about 70 per-cent of the amide groups have been converted to carboxyl groups and then neutralized with ammonium or an alkali metal hydroxide.
The most preferred water soluble synthetic polymer for use as a gelling agent in accordance with the present invention is a polyacrylamide polymer which has been hydrolyzed such that about O to 30 percent of the amide groups have been converted to car-boxyl groups and the carboxyl groups neutralized with an alkali ~0 metal or ammonium hydroxide.
Water soluble derivative~ of cellulose suitable for use as gelling agents in accordance with the present inven-tion include, but are not limited to, hydroxyethylcellulose, carboxymethylhydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, propylcellulose and sulfo-propylcellulose. Of these, hydroxyethylcellulose and carboxy-methylhydroxyethylcellulose are preferred.
..
.
Suitable water soluble polysaccharides are guar gum, locust bean gum, and gum tragacanth. Water soluble deriva-tives of the ~oregoing polysaccharide compounds can also be utilized as gelling agents, e.g., hydroxyethyl guar gum, hydroxypropyl guar gum and carboxymethyl guar gum. Of the various polysaccharides which can be used, guar gum i9 pre-ferred.
The preferred gelling agents mentioned above, i.e., polyacrylamide polymers which have been hydrolyzed and neutral-ized, hydroxyethylcellulose, carboxymethylhydroxyethylcellu-lose and guar gum are readily commercially available and form stable gels of desired viscosity when added to aqueous liquids at relatively low concentrations.
Gelling agent concentrations of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid are generally required. At concentrations below about 0.1 part hy weight gelling agent per 100 parts by weight aqueou~ liquid, the resulting gel does not have sufficient viscosity to achieve desired objectives, e.g., to adequately maintain propping agents in suspension. At concentrations above about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid, the resulti~g com-position is generally of such a high viscoty that excessive ~ -friction losses are encountered when displacing the composi-tion through a conduit at high velocities. When using the preferred gelling agents mentioned above, they ~0~0~40 are preferably added to the aqueous liquid in an amount of about 0.25 to about 1.5 parts by weight gelling agent per 100 parts by weight aqueous liquid.
The free radical generating agents useful in accordance with the present invention are water soluble oxidizing agents having the property of generating free radicals for degrading ~ -the gelling agent. Such oxidizing agents include water soluble perixide compounds, persulfate compounds, or mixtures thereof. Examples of preferred and particularly suitable water soluble peroxide compounds include, but are not limited to, hydrogen peroxide, tertiary butyl hydroperoxide and di-tertiary butyl peroxide. Preferred water soluble persulfates include ammonium persulfate and the alkali metal persulfates.
The foregoing free radical generating agents are utilized in the compositions of the present invention in an amount of about 0.0001 to about 2 parts by weight free radical generator per 100 parts by weight aqueous liquid.
At a concentration below about 0.0001 part free radical generator per 100 parts aqueous liquid, the rate of degra-dation of the gelling agent is low and the time required for breaking the gel is generally too long. Above a con-centration of about 2 parts by weight free radical generator per 100 parts by weight aqueous liquid) excess free radicals are generated. When utilizing the preferred free radical generating agents mentioned above, they are combined with the aqueous liquid and gelling agent in an amount of about 0.001 to about 0.75 parts by weight free radical generator per 100 parts by weight aqueous liquid.
10~ 4(~
Reducing agents which are suitable for use in accordance with the present invention and which function to accelerate the generation of free radicals over an extended period of time at low temperatures are water soluble metal salts wherein the oxidation number of the metal ion is less than -the highest possible oxidation number for that ion. Examples of such salts are the cuprous, ferrous, stannous, cobaltous, chromous, nickelous, titanous, manganous and arsenous salts of the halides, sulfates and nitrates. Of these, cuprous chloride, ferrous chloride and cobaltous chloride are preferred in that they have a limited solubility in aqueous fluids, and as a result the aqueous treating compositions of the present invention including these salts remain gelled for periods of time long enough to place and utilize the compositions in subterranean well formations. That is~
the reducing agent dissolves slowly so that the reactivity of the free radical generating agent is not accelerated too quickly. The metal salt used is preferably included in the treating composition in an amount at least equal to the amount required to stoichiometrically react with the free radical generating agent present in the composition. This concentration is generally about 0.1 to about 7.5 parts by weight metal salt per 100 parts by weight aqueous liquid.
While the novel gelled aqueous compositions of the present invention have a variety of uses in treating low temperature subterranean well formations, the compositions ~ -are particularly suitable as fracturing fluids. That is, the gelled aqueous compositions can be formed with a ~ ~
': ' .: ~:: .
10~0640 viscosity sufficient to bring about the fracturing of a well formation using conventional techniques. Further, the gelled aqueous compositions are able to maintain solid particulated propping agents in suspension so that the propping agent can be placed in the fractures thereby preventing them from closing.
In carrying out the methods of the present invention for treating a low temperature subterranean formation penetrated by a well bore, an aqueous ~elled composition of the present in-vention can be prepared on the surface by mixing the gelling agent and the reducing agent with a quantity of aqueous liquid at atmospheric temperatures. The free radical generating agent is then added to the aqueous liquid and the resulting gelled aqueous composition is introduced into the formation, usually by pumping the gelled aqueous composition through a string of pipe disposed in the well bore. Once the treatment of the formation is completed, a sufficient time period is allowed for the gelled aqueous composition to break or revert to a thin fluid. As stated previously, even at well formations existing at temperatures as~low as 70F~-,) only a relatively short period of time is required for the gelled aqueous com-positions to break. Once broken, the aqueous liquid returns to the well bore, along with fluids produced from the subterran- -ean formation.
The invention relates to a method for reducing the viscosity of an aqueous gel, said method consisting essentially of: mixing with said aqueous gel a water soluble oxidizing agent having the property of generating free radicals, and a water soluble reducing agent to accelerate the generation of said free radicals, and subjecting said aqueous gel containing said ox~dizing agent and said reducing agent to temperatures of up to about 120bF for a time sufficient to reduce the viscosity of said aqueous gel;
~ -8-A~. ,.
.,.. ,,, . , . .. , . - ~ .
106C)640 wherein said reducing agent is a water soluble metal salt, selected from the group consisting of cuprous, ferrous, stannous, cobaltous, chromous, nickelous, titanous, manganous and arsenous salts of the halides, sulfates and nitrates and mixtures thereof: and said reducing agent is present in said composition in an amount in the range of from about 0.1 to about 7.5 parts by weight per 100 parts by weight aqueous liquid, and wherein said oxidizing agent is selected from the group consist-ing of water soluble peroxide compounds, water soluble persulfate compounds and mixtures thereof and said oxidizing agent is pre-sent in an amount of about 0.0001 to about 2 parts by weight free radical generating agent per 100 parts by weight aqueous liquid:
and wherein said aqueous gel is comprised of an aqueous liquid and a water soluble organic gelling agent present in an amount of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid sufficient to increase viscosity :
of said aquous gel to a desired level; and further wherein said -:;
organic gelling agent is selected from the group consisting of sodium polyacrylate, polyacrylic acid, polysodium-2-acrylamide-3-propylsulfonate, polyacrylamides and polymethacrylamides hydrolyzed to convert from 0 to about 70 percent of amide groups -to carboxyl groups which are then neutralized with ammonium or an alkali metal hydroxide, guar gum, locust bean gum, gum traga- :
canth, hydroxyethyl guar gum, hydroxypropyl guar gum, carboxy-methyl guar gum and mixtures thereof. :
In fracturing a low temperature subterranean formationaccording to the method of the present invention, a gelled aqueous composition o~ the invention can be - 8a -1~60640 prepared with a quantity of solid particulated propping agent suspended therein. In preparing the composition, the propping agent i9 preferably added to a quantity of aqueous liquid prior to or simultaneously with the gelling agent and reduc-ing aqent and the mixture vigorously agitated to form the gel with propping agent uniformly distributed therein. The free radical generating agent is added to the composition while being agitated, and the composition is then introduced into the formation and forced into fractures created therein BO
that the propping agent is placed in the fractures. After the propping agent has been placed, the composition is allowed to revert to a thin 1uid and recovered leaving the propping agent in the fractures so that they are held open. A~ will be understood by those skilled in the art, the recovery of the treating composition can be accomplished in a variety of way~, but generally simply involves placing the treated well formation on production so that the fluids are produced back-along with natural fluids from the formation.
In order to present a clear understanding of the present invention the following examples are given:
Example 1 A gelled a~ueous composition is prepared in the labor-atory by dissolving a mixture of 4.8 grams (the equivalent of 80 ~ounds per 1000 gallons) of guar gum and 0.3 grams of ferrous sulfate in 500 milliliters of tap water. A highly viscous aqueou~ composition i~ formed at a temperature of 70F. 0.3 1060~40 grams of potassium persulfate are then added to the aqueous composition and the mixt~e is viyorously agitated with the result that the composition reverts to a thin fluid having a viscosity of less than 2 centipoises.
Example 2 A gelled aqueous composition is prepared in the laboratory by dissolving 4.8 grams of hydroxyethylcellulose and 0.3 grams of ferrous sulfate in 500 milliliter.s of tap water.
A highly viscous aqueous composition is formed at a tempera-ture of 70F. 0.3 grams of potassium persulfate are added to the composition and upon vigorous agitation the composi-tion reverts to a thin fluid having a low Vlscosity.
Example 3 A polyacrylamide polymer mixture,hydrolyzed such that from about 0 to about 30 percent of the amide groups are Y
converted to carboxyl groups and then neutralized with sodium hydroxide, is added to 500 milliliters of tap water in an amount of 4.8 grams, along with 0.3 grams of ferrous ~ -sulfate. A gelled aqueous composition at a temperature of 70F is formed. 0O3 grams of potassium persulfate are added to the aqueous composition and after vigorous agi-tation the composition reverts to a thin fluid having a viscosity of less than 2 centipoises.
While the gelled aqueous compositions of the present --invention are particularly suitable for carrying out frac-turing and fracture propping operations in low temperature subterranean well formations, the compositions are not so limited in that they can be utilized for carrying out ' -: . , . . . . ~ . ... .. ; .
~0~;0~i40 numerous other operations. As will be understood by those skilled in the art, many variations, both as to methods of utilizing the compositions and in the relative propor-tions of components of the compositions can be made without departing from the scope of this invention. Furthermore, additional components and/or additives can be incorporated with the compositions to bring about desired properties such as the reduction of fluid loss, etc. The invention should be limited only by the lawful scope of the appended claims.
.. .. . . .
Claims (22)
1. An aqueous composition for treating subterranean formations having temperatures of up to about 120°F comprising:
- an aqueous liquid, a water soluble organic gelling agent present in said aqueous liquid in an amount of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid sufficient to increase the viscosity thereof, a water soluble oxidizing agent having the property of generating free radicals, and a water soluble reducing agent to accelerate the generation of said free radicals;
- wherein said reducing agent is a water soluble metal salt, selected from the group consisting of cuprous, ferrous, stannous, cobaltous, chromous, nickelous, titanous, manganous and arsenous salts of the halides, sulfates and nitrates and mixtures thereof; and said reducing agent is present in said composition in an amount in the range of from about 0.1 to about 7.5 parts by weight per 100 parts by weight aqueous liquid; and - wherein said oxidizing agent is selected from the group consisting of water soluble peroxide compounds, water soluble persulfate compounds and mixtures thereof and said oxidizing agent is present in an amount of about 0.0001 to about 2 parts by weight free radical generating agent per 100 parts by weight aqueous liquid; and further - wherein said organic gelling agent is selected from the group consisting of sodium polyacrylate, polyacrylic acid, polysodium-2-acrylamide-3-propylsulfonate, polyacrylamides and polymethacrylamides hydrolyzed to convert from 0 to about 70 percent of amide groups to carboxyl groups which are then neutralized with ammonium or an alkali metal hydroxide; guar gum, locust bean gum, gum tragacanth, hydroxyethyl guar gum, hydroxy-propyl guar gum, carboxymethyl guar gum and mixtures thereof.
- an aqueous liquid, a water soluble organic gelling agent present in said aqueous liquid in an amount of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid sufficient to increase the viscosity thereof, a water soluble oxidizing agent having the property of generating free radicals, and a water soluble reducing agent to accelerate the generation of said free radicals;
- wherein said reducing agent is a water soluble metal salt, selected from the group consisting of cuprous, ferrous, stannous, cobaltous, chromous, nickelous, titanous, manganous and arsenous salts of the halides, sulfates and nitrates and mixtures thereof; and said reducing agent is present in said composition in an amount in the range of from about 0.1 to about 7.5 parts by weight per 100 parts by weight aqueous liquid; and - wherein said oxidizing agent is selected from the group consisting of water soluble peroxide compounds, water soluble persulfate compounds and mixtures thereof and said oxidizing agent is present in an amount of about 0.0001 to about 2 parts by weight free radical generating agent per 100 parts by weight aqueous liquid; and further - wherein said organic gelling agent is selected from the group consisting of sodium polyacrylate, polyacrylic acid, polysodium-2-acrylamide-3-propylsulfonate, polyacrylamides and polymethacrylamides hydrolyzed to convert from 0 to about 70 percent of amide groups to carboxyl groups which are then neutralized with ammonium or an alkali metal hydroxide; guar gum, locust bean gum, gum tragacanth, hydroxyethyl guar gum, hydroxy-propyl guar gum, carboxymethyl guar gum and mixtures thereof.
2. The composition of claim 1 wherein said oxidizing agent is selected from the group consisting of hydrogen peroxide, tertiary butyl hydroperoxide, di-tertiary butyl peroxide, ammonium persulfate, and alkali metal persulfate, and mixtures thereof.
3. The composition of claim 2 wherein said reducing agent is selected from the group consisting of cuprous chloride, ferrous chloride, cobaltous chloride, and mixtures thereof.
4. The composition of claim 3 wherein said oxidizing agent is present in an amount of about 0.001 to about 0.75 parts by weight per 100 parts by weight aqueous liquid.
5. The composition of claim 4 wherein said gelling agent is polyacrylamide which has been hydrolyzed such that from about 0 to about 30 percent of the amide groups have been converted to carboxyl groups and then neutralized with an ammonium or alkali metal hydroxide, said polyacrylamide being present in said composition in an amount of about 0.25 to about 1.5 parts by weight gelling agent per 100 parts by weight aqueous liquid.
6. The composition of claim 4 wherein said gelling agent is guar gum present in said composition in an amount of about 0.25 to about 1.5 parts by weight guar gum per 100 parts by weight aqueous liquid.
7. The composition of claim 1 wherein said gelling agent is selected from the group consisting of polymethacrylamide, polyacrylamide, sodium polyacrylate, polyacrylic acid, poly-sodium-2-acrylamide-3-propyl-sulfonate and mixtures thereof.
8. The composition of claim 1 wherein said gelling agent is selected from the group consisting of guar gum, locust bean gum, gum tragacanth, and mixtures thereof.
9. The composition of claim 1 wherein said gelling agent is selected from the group consisting of hydroxyethyl guar gum, hydroxypropyl guar gum, carboxymethyl guar gum and mixtures thereof.
10. The composition of claim 1 wherein said oxidizing agent is a water soluble peroxide selected from the group consisting of hydrogen peroxide, tertiary butyl hydroperoxide, di-tertiary butyl peroxide, and mixtures thereof, said water*
11. The composition of claim 1 wherein said oxidizing agent is a water soluble persulfate selected from the group consisting of ammonium persulfate, alkali metal persulfates, and mixtures thereof, said water soluble persulfate compound being present in said composition in an amount of about 0.001 to about 0.75 parts by weight persulfate compound per 100 parts by weight aqueous liquid.
12. The composition of claim 1 wherein the reducing agent is selected from the group consisting of cuprous chloride, ferrous chloride, cobaltous chloride, and mixtures thereof.
13. A method for reducing the viscosity of an aqueous gel, said method consisting essentially of:
- mixing with said aqueous gel a water soluble oxidizing agent having the property of generating free radicals, and a water soluble reducing agent to accelerate the generation of said free radicals, and - subjecting said aqueous gel containing said oxidizing agent and said reducing agent to temperatures of up * soluble peroxide compound being present in said composition in an amount of about 0.001 to about 0.75 parts by weight peroxide compound per 100 parts by weight aqueous liquid to about 120°F for a time sufficient to reduce the viscosity of said aqueous gel, - wherein said reducing agent is a water soluble metal salt, selected from the group consisting of cuprous, ferrous, stannous, cobaltous, chromous, nickelous, titanous, manganous and arsenous salts of the halides, sulfates and nitrates and mixtures thereof; and said reducing agent is present in said composition in an amount in the range of from about 0.1 to about 7.5 parts by weight per 100 parts by weight aqueous liquid, and - wherein said oxidizing agent is selected from the group consisting of water soluble peroxide compounds, water soluble persulfate compounds and mixtures thereof and said oxidizing agent is present in an amount of about 0.0001 to about 2 parts by weight free radical generating agent per 100 parts by weight aqueous liquid, and - wherein said aqueous gel is comprised of an aqueous liquid and a water soluble organic gelling agent present in an amount of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid sufficient to increase viscosity of said aqueous gel to a desired level;
and further - wherein said organic gelling agent is selected from the group consisting of sodium polyacrylate, polyacrylic acid, polysodium-2-acrylamide-3-propyl-sulfonate, polyacrylamides and polymethacrylamides hydrolyzed to convert from 0 to about 70 percent of amide groups to carboxyl groups which are then neutralized with ammonium or an alkali metal hydroxide, guar gum, locust bean gum, gum tragacanth, hydroxyethyl guar gum, hydroxypropyl guar gum, carboxymethyl guar gum and mix-tures thereof.
- mixing with said aqueous gel a water soluble oxidizing agent having the property of generating free radicals, and a water soluble reducing agent to accelerate the generation of said free radicals, and - subjecting said aqueous gel containing said oxidizing agent and said reducing agent to temperatures of up * soluble peroxide compound being present in said composition in an amount of about 0.001 to about 0.75 parts by weight peroxide compound per 100 parts by weight aqueous liquid to about 120°F for a time sufficient to reduce the viscosity of said aqueous gel, - wherein said reducing agent is a water soluble metal salt, selected from the group consisting of cuprous, ferrous, stannous, cobaltous, chromous, nickelous, titanous, manganous and arsenous salts of the halides, sulfates and nitrates and mixtures thereof; and said reducing agent is present in said composition in an amount in the range of from about 0.1 to about 7.5 parts by weight per 100 parts by weight aqueous liquid, and - wherein said oxidizing agent is selected from the group consisting of water soluble peroxide compounds, water soluble persulfate compounds and mixtures thereof and said oxidizing agent is present in an amount of about 0.0001 to about 2 parts by weight free radical generating agent per 100 parts by weight aqueous liquid, and - wherein said aqueous gel is comprised of an aqueous liquid and a water soluble organic gelling agent present in an amount of about 0.1 to about 10 parts by weight gelling agent per 100 parts by weight aqueous liquid sufficient to increase viscosity of said aqueous gel to a desired level;
and further - wherein said organic gelling agent is selected from the group consisting of sodium polyacrylate, polyacrylic acid, polysodium-2-acrylamide-3-propyl-sulfonate, polyacrylamides and polymethacrylamides hydrolyzed to convert from 0 to about 70 percent of amide groups to carboxyl groups which are then neutralized with ammonium or an alkali metal hydroxide, guar gum, locust bean gum, gum tragacanth, hydroxyethyl guar gum, hydroxypropyl guar gum, carboxymethyl guar gum and mix-tures thereof.
14. The method of claim 13 wherein said oxidizing agent is selected from the group consisting of hydrogen peroxide, tertiary butyl hydroperoxide, di-tertiary butyl peroxide, ammonium persulfate, an alkali metal persulfate, and mixtures thereof.
15. The method of claim 14 wherein said reducing agent is selected from the group consisting of cuprous chloride, ferrous chloride, cobaltous chloride, and mixtures thereof.
16. The method of claim 15 wherein said oxidizing agent is present in an amount of about 0.001 to about 0.75 parts by weight per 100 parts by weight aqueous liquid.
17. The method of claim 16 wherein said gelling agent is polyacrylamide which has been hydrolyzed such that from about 0 to about 30 percent of the amide groups have been converted to carboxyl groups and then neutralized with an ammonium or alkali metal hydroxide, said polyacrylamide being present in said composition in an amount of about 0.25 to about 1.5 parts by weight gelling agent per 100 parts by weight aqueous liquid.
18. The method of claim 16 wherein said gelling agent is guar gum present in said composition in an amount of about 0.25 to about 1.5 parts by weight guar gum per 100 parts by weight aqueous liquid.
19. The method of claim 13 wherein said gelling agent is selected from the group consisting of polyacrylamide, which has been hydrolyzed such that from about 0 to about 30 percent of the amide groups have been converted to carboxyl groups and then neutralized with an ammonium or alkali metal hydroxyde, hydroxyethylcellulose, carboxymethylhydroxyethylcellulose, guar gum, and mixtures thereof.
20. The method of claim 13 wherein said oxidizing agent is a water soluble peroxide selected from the group consisting of hydrogen peroxide, tertiary butyl hydroperoxide, di-tertiary butyl peroxide, and mixtures thereof, said water soluble peroxide compound being present in said composition in an amount of about 0.001 to about 0.75 parts by weight peroxide compound per 100 parts by weight aqueous liquid.
21. The method of claim 13 wherein said oxidizing agent is a water soluble persulfate selected from the group consist-ing of ammonium persulfate, alkali metal persulfates, and mixtures thereof, said water soluble persulfate compound being present in said composition in an amount of about 0.001 to about parts by weight persulfate compound per 100 parts by weight aqueous liquid.
22. The method of claim 13 wherein the reducing agent is selected from the group consisting of cuprous chloride, ferrous chloride, cobaltous chloride, and mixtures thereof.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US44687074A | 1974-02-28 | 1974-02-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1060640A true CA1060640A (en) | 1979-08-21 |
Family
ID=23774127
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA210,087A Expired CA1060640A (en) | 1974-02-28 | 1974-09-25 | Methods and compositions for treating low temperature subterranean well formations |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1060640A (en) |
-
1974
- 1974-09-25 CA CA210,087A patent/CA1060640A/en not_active Expired
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