CA1186883A

CA1186883A - Breaker system for hydraulic fracturing fluids

Info

Publication number: CA1186883A
Application number: CA000418104A
Authority: CA
Inventors: Clare H. Kucera; Richard B. Connell
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1982-12-20
Filing date: 1982-12-20
Publication date: 1985-05-14

Abstract

ABSTRACT OF THE DISCLOSURE

Aqueous compositions having properties making them suitable for use as hydraulic fracturing fluids are disclosed. These compositions comprise (a) an uncrosslinked aqueous polysaccharide solution, and (b) a 4,4'-thiodiphenol. Ingredient (b) acts as a "breaker" and causes the composition to lose viscosity at a controlled rate.

Description

BREAKER SYSTEM FOR
HYDRAULIC FRACTURING FLUIDS

This invention pertains to novel aqueous compositions comprising an uncrosslinked a~ueous poly-saccharide solution, and a 4,4'-thiodiphenol. The a~ueous compositions have properties making the compo-sition suitable for use as a hydraulic fracturingfluid.

The use of aqueous solutions of polysaccha-rides as hydraulic fracturing fluids is well known.
The polysaccharides add desirable viscosity properties to the aqueous hydraulic fluids and give such fluids better proppant carrying capacity. Various chemical and en~yme breakers have been added to such hydraulic fluids to reduce the viscosity of the fluids after they have served their purpose. It is thought that these breakers work by degrading the polymer structure.

Typical polysaccharides tha-t have been used in preparing hydraulic fluids include guar, hydroxy-propyl guar, carboxymethylcellulose, hydroxyethyl-cellulose, and the like. Such polysaccharides and 29,125-F -1-polysaccharide derivatives form a known class of compounds.

The polysaccharides were added in amounts to give the desired viscosity. Typically the polysaccharide was added in amounts of up to about 80 pounds of polymer, dry weight basis, per 1000 gallons of formulated fluid.
The most common range is from 20 to 80 pounds of polymer per thousand gallons.

The breakers used in such hydraulic frac-turing systems also form a known class of compounds.Examples include the alkali metal persulfa-tes (e.g., sodium persulfate, potassium persulfate, etc.~ and ammonium persulfate, and the like. Of these, the most commonly used compounds are sodium persulfate and ammonium persulfate.

These persulfate breakers were added in amounts sufficient to "break" the viscosity of the viscous liquid under the downhole conditions of temperature and pressure. The persulfate breakers are exceedingly effective, and that is their drawback as well as their benefit. From time to kime, it would be advantageous to have a slower or more controlled rate of reaction during this thinning process. This would extend the "pot life" or workability time during which the fluids could be utilized as the hydraulic frac-turing fluid before the viscosity became too low to be usable.

This invention resides in a composition having properties making it suitable for use as a hydraulic fracturing fluid, said composition comprising:

29,125-F -2-(a) an uncrosslinked aqueous polysaccharide solution, and (b) 4,4'--thiodiphenol or an inertly sub-stituted 4,4 7 -thiodlphenol.

The novel aqueous composition has desirable initial viscosities and a rate of "break" under down-hole conditions that is considered to be highly desirable.

By the term "breaker" is meant a chemical compound that will reduce the viscosity of an agueous fluid thickened with a polysaccharide or polysaccharide derivative. The term "breaking" is applied to the process in which the viscosity of such a hydraulic fluid is lowered. This is the customary usage of such terms in the industry.

The novel a~ueous compositions, as noted above, comprise an uncrosslinked agueous polysaccharide solution. Any of the known class of polysaccharides can be suitably used herein at conventional loadings.
However, the subgenus of compounds referred to in the industry as galactomannans are preferred, and hydroxy-propyl guar is most preferred. Loading levels of from 20 to 80 pounds of polysaccharide are customarily preferred.

The novel compositions contain a 4,4'-thiodi-phenol. This compound corresponds to the structural formula A J~~\
I HO ~ S ~ OH
~)1 or 2 (R)l or 2 29,125-F -3-each R independently is an inert substituen-t, such as hydro~en, hydroxyl, carbo~yl, hydroxymethyl, halomethyl (e.g., chlorome-thyl, bromoethyl, etc.) bis(C1-C4 alkyl) aminomethyl, aminomethyl, (C1-C4) alkylthiomethyl, mercaptomethyl, alkyl (e.g., methyl, ethyl, propyl, isobutyl, etc.), -CH2SO3 M where M is an alkali metal, and the like. The 4,4'-thiodiphenols form a known class of compounds with known methods of preparation. It is added in amounts sufficient to break the viscosity of the compositions. Normally, amounts of up to 5 pounds per 1000 gallons of formulated fluid are used and, in many instances, from 0.75 to 1.5 pounds per 1000 gallons is sufficient.

The actual amounts of the 4,4'-thiodiphenol that will be added will vary depending upon the poly-saccharides chosen, the loading level of the poly-saccharide, and the desired rate of break. Fortunately, the viscosity measurements and optimization of propor-tion of ingredients is easily within the skill of the art and does not require any undue experimentation.
Thus, the skilled artisan can tailor the composition to fulfill a particular need.

Conventional additives for hydraulic fracturing fluids can be included in the present aqueous compositions, if desired. For example, in many instances it is desirable to add a proppant to the composition if it is to be used as a hydraulic fracturing fluid. Typical proppants include sand (usually 20/40 mesh sand), sintered bauxite, glass beads, etc. In other instances it is desirable to add a gas to the fracturing fluid to "energize" the fluid.

29,125-F -4-For e~ample, it is conventional to add gaseous carbon dioxide or nitrogen to hydraulic fracturing fluids.
These materials as well as other conventional additives are well known or obvious to the skilled artisan, as are other uses for the novel compositions.

Experimental:
In a series of experiments, a solution was prepared by blending hydroxypropyl guar (HPG) in fresh water at a loading level of 40 pounds of HPG per 1000 gallons of water (lbs/1000 gal). 4,4'-Thiodiphenol (TDP) was then added with stirring and the viscosity of the resulting solution was measured over a period of time using a Fann 50 C model rotational viscometer at 170 reciprocal seconds. The data are summarized in Table I.

TABLE I
Viscoslty (cps) Run Additive(s)lbs/1000 gal 1 hr 2 hr 3 hr 4 hr 1 Control None 14.1 11.7 9.6 7.9

2 (NH4)2S2O8 5 l.0 0.9 0.6 0.6

3 Na2S2O8 5 1.0 0.8 0.6 0.6

4 TDP 1 12.4 7.0 4.0 2.4 TDP 5 7.6 4.6 3.6 2.0 These data show that 4,4'-thiodiphenol is useful as a breaker and that the rate of break is more controlled and much slower than the persulfate breakers.
This provides a longer period of workability for the present compositions.

29,125-F -5-

Claims

CLAIMS:

1. A composition having properties making it suitable for use as a hydraulic fracturing fluid, said composition comprising:
(a) an uncrosslinked aqueous polysaccharide solution, and (b) 4,4'-thiodiphenol or an inertly sub-stituted 4,4'-thiodiphenol.

2. The composition defined by Claim 1 wherein said polysaccharide is a galactomannan.

3. The composition defined by Claim 1 wherein said polysaccharide is guar, hydroxypropylguar, carboxyl-methylcellulose or hydroxyethylcellulose.

4. The composition defined by Claim 3 wherein said polysaccharide is hydroxypropylguar.

5. The composition defined by Claim 2 wherein (b) is present in amounts of up to 5 pounds per 1000 gallons of the composition.

6. In a process of fracturing a subterranean earth formation by injecting a hydraulic fracturing fluid into a wellbore under elevated pressure, the improvement comprising using the composition of Claim 1 as the hydraulic fracturing fluid.