US 4,068,720 A · Method for acidizing subterranean formations

Abstract

Gelled acidic compositions suitable for either matrix acidizing or fracture-acidizing of subterranean formations, and methods of using said compositions in acidizing operations, are provided. Said compositions comprise water, a water-soluble cellulose ether, an acid, a water soluble compound of a polyvalent metal wherein the metal can be reduced to a lower polyvalent valence state and cause gelation of the water containing said cellulose ether and said acid, and a reducing agent capable of reducing said metal and causing said gelation.

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Claims21

Dependent claims

A method for acid treating a porous subterranean formation susceptible of attack by an acid and penetrated by a well bore, which method comprises:

injecting into said formation via said well bore a gelled acidic composition comprising
water;
an amount of a water-soluble cellulose ether which is sufficient to thicken said water;
an amount of a water-soluble compound of a polyvalent metal wherein the metal present is capable of being reduced to a lower polyvalent valence state and which is sufficient to cause gelation of an aqueous dispersion of the components of said composition when the valence of at least a portion of said metal is reduced to said lower valence state;
an amount of a water-soluble reducing agent which is effective to reduce at least a portion of said metal to said lower valence state and cause said gelation;
an amount of a non-oxidizing acid which is capable of reacting with a significant amount of the acid-soluble components of said formation;
said cellulose ether, said polyvalent metal compound, said reducing agent, and said acid, in the amounts used, being sufficiently compatible with each other in an aqueous dispersion thereof to permit said gelation and thus form a said composition having sufficient stability to degeneration by the heat of said formation to permit good penetration of said composition into said formation;
and
maintaining said composition in said formation in contact therewith for a period of time usually sufficient for the acid in said composition to significantly react with the acid-soluble components of said formation and stimulate the production of fluids therefrom.

6 more elements

A method for acid treating a porous subterranean formation susceptible of attack by an acid and pentrated by a well bore, which method comprises:

injecting into said formation via said well bore a gelled acidic composition comprising
water;
an amount of a water-soluble cellulose ether which is sufficient to thicken said water;
an amount of a water-soluble compound of a polyvalent metal wherein the metal present is capable of being reduced to a lower polyvalent valence state and which is sufficient to cause gelation of an aqueous dispersion of the components of said composition when the valence of at least a portion of said metal is reduced to said lower valence state;
an amount of a water-soluble reducing agent which is effective to reduce at least a portion of said metal to said lower valence state and cause said gelation;
an amount of a non-oxidizing acid which is capable of reacting with a significant amount of the acid-soluble components of said formation;
said cellulose ether, said polyvalent metal compound, said reducing agent, and said acid, in the amounts used, being sufficiently compatible with each other in an aqueous dispersion thereof to permit said gelation and thus form a said composition having sufficient stability to degeneration by the heat of said formation to permit good penetration of said composition into said formation;
and
maintaining said composition in said formation in contact therewith for a period of time usually sufficient for the acid in said composition to significantly react with the acid-soluble components of said formation and stimulate the production of fluids therefrom;
said gelled acidic composition being prepared and injected into said formation by the following combination of steps:
a. dispersing said cellulose ether in said water;
b. pumping said water containing said cellulose ether into said well via a suitable conduit;
c. then introducing one of said polyvalent metal compound component and said acid component into said conduit during said pumping;
d. then during said pumping, introducing the other of said polyvalent metal compound component and said acid component, which was not introduced in said step (c), into said conduit downstream from the point of introduction in said step (c);
and
e. then during said pumping, introducing said reducing agent into said conduit downstream from the point of introduction in said step (d).

13 more elements

A method for acid treating a porous subterranean formation susceptible of attack by an acid and penetrated by a well bore, which method comprises:

injecting into said formation via said well bore a gelled acidic composition comprising
water;
an amount of a water-soluble cellulose ether which is sufficient to thicken said water;
an amount of a water-soluble compound of a polyvalent metal wherein the metal present is capable of being reduced to a lower polyvalent valence state and which is sufficient to cause gelation of an aqueous dispersion of the components of said composition when the valence of at least a portion of said metal is reduced to said lower valence state;
an amount of a water-soluble reducing agent which is effective to reduce at least a portion of said metal to said lower valence state and cause said gelation;
an amount of a non-oxidizing acid which is capable of reacting with a significant amount of the acid-soluble components of said formation;
said cellulose ether, said polyvalent metal compound, said reducing agent, and said acid, in the amounts used, being sufficiently compatible with each other in an aqueous dispersion thereof to permit said gelation and thus form a said composition having sufficient stability to degeneration by the heat of said formation to permit good penetration of said composition into said formation;
and
maintaining said composition in said formation in contact therewith for a period of time usually sufficient for the acid in said composition to significantly react with the acid-soluble components of said formation and stimulate the production of fluids therefrom;
said gelled acidic composition being prepared and injected into said formation by the following combination of steps:
a. dispersing said cellulose ether in said water;
b. then initiating pumping of said water containing said cellulose ether into said well via a suitable conduit;
c. then introducing said polyvalent metal compound into said conduit;
d. then introducing said reducing agent into said conduit downstream from the point of introduction of said polyvalent metal compound;
and
e. then introducing said acid into said conduit downstream from the point of introduction of said reducing agent.

13 more elements

Dependencies are inferred from the claim text.

Description8,057 words

Summary4,717 words

#This invention relates to acid treating or acidizing of subterranean formations.

#Acid treating or acidizing of porous subterranean formations penetrated by a well bore has been widely employed for increasing the production of fluids, e.g., crude oil, natural gas, etc., from said formations. The usual technique of acidizing a formation comprises introducing a non-oxidizing acid into the well under sufficient pressure to force the acid out into the formation where it reacts with the acid-soluble components of the formation. The technique is not limited to formations of high acid solubility such as limestone, dolomite, etc. The technique is also applicable to other types of formations such as a sandstone containing streaks or striations of acid soluble components such as the various carbonates.

#Durng the acid treating operation, passageways for fluid flow are created in the formation, or existing passageways therein are enlarged, thus stimulating the production of fluids from the formation. This action of the acid on the formation is often called etching. Acid treating or acidizing operations wherein the acid is injected into the formation at a pressure or rate insufficient to create cracks or fractures in the formation is usually referred to as matrix acidizing.

Detailed description3,340 words

#The following examples will serve to further illustrate the invention, but should not be considered as unduly limiting on the invention.

#An aqueous solution containing 5000 ppm of sodium carboxymethylcellulose (CMC9H) having a degree of substitution of about 0.9 was treated to contain 1000 ppm Na.sub.2 Cr.sub.2 O.sub.7.2H.sub.2 O and 800 ppm NaHSO.sub.3. After stirring two minutes, the solution was diluted with an equal volume of 20 percent acetic acid to give a solution containing about 10 weight percent acid. Thirty minutes later sufficient gelation had taken place to result in an apparent viscosity (Model 35 Fann V-G Meter) of 400 cp at 10 sec.sup.-1.

#In a manner similar to that of Example I, a 10,000 ppm aqueous solution of that same soluble cellulose ether was treated to contain 1500 ppm Na.sub.2 Cr.sub.2 O.sub.7.2H.sub.2 O and 7500 ppm potassium iodide. After stirring 2 minutes, the solution was diluted with an equal volume of 98 percent acetic acid to give a solution containing about 49 weight percent acetic acid. After 25 to 30 minutes sufficient gelation had taken place to result in an apparent viscosity (Model 35 Fann V-G Meter) of 750 cp at 10 sec.sup.-1.

Facts

Application

05/643,985Filed 24 Dec 1975

Granted

17 Jan 1978

Term ended

17 Jan 1995

Estimated · how

Pre-1995 term; greater of 17 years from grant or 20 years from filing when eligible. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification7 codes

E21B 43/24
Enhanced recovery methods for obtaining hydrocarbons: using heat, e.g. steam injection
C09K 8/76
Combined with additives added for specific purposes: for preventing or reducing fluid loss
C09K 8/90
Macromolecular compounds: of natural origin, e.g. polysaccharides, cellulose
Y10S 507/903
Earth boring, well treating, and oil field chemistry: crosslinked resin or polymer

Method for acidizing subterranean formations

Life of this patent

Method for acidizing subterranean formations

Life of this patent

Life of this patent

Abstract

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Drawings

Claims21

Description8,057 words

Drawings

Classification7 codes

Life of this patent

Description8,057 words