WO2014151284A1

WO2014151284A1 - Method and composition for hydraulic fracturing

Info

Publication number: WO2014151284A1
Application number: PCT/US2014/025372
Authority: WO
Inventors: Kimberley D. MAC EWAN; Reinaldo C. NAVARRETE
Original assignee: Meadwestvaco Corporation
Priority date: 2013-03-15
Filing date: 2014-03-13
Publication date: 2014-09-25

Abstract

A method of fracturing a subterranean formation wherein: (a) a hydraulic fracturing fluid is injected into said subterranean formation, (b) the fracturing fluid includes a traceable polymer, and (c) the fluid produced from the well is analyzed to determine if the traceable polymer is present in the fluid. The traceable polymer also preferably operates as a friction reducing polymer or as a viscosifying polymer in the hydraulic fracturing fluid.

Description

METHOD AND COMPOSITION FOR

HYDRAULIC FRACTURING

Related Case

[0001] This application claims the benefit of U.S. Provisional Patent Application

Serial No. 61/786,650 filed on March 15, 2013 and incorporates said provisional application by reference into this document as if fully set out at this point.

Field of the Invention

[0002] The present invention relates to methods and compositions for hydraulic fracturing using traceable polymers.

Background of the Invention

[0003] In conducting hydraulic fracturing operations, microseismic analyses or other techniques can be used to determine the position, length, and height of each fracture. However, when, for example, a horizontal well extending through a shale formation is fractured in multiple stages, the microseismic analysis techniques are essentially unable to determine which of the fractured stages are successfully producing oil and/or gas products and which are not. Nor does this analysis provide an indication of either (a) the quantitative production rate from any given stage or (b) the relative/comparative rates of production from multiple stages. Consequently, a need exists for a method for reliably obtaining such information for each stage of either a single or a multiple stage hydraulic fracturing operation.

Summary of the Invention

[0004] The present invention provides a method and composition for fracturing a subterranean formation which satisfy the needs and alleviate the problems discussed above.

[0005] In one aspect, there is provided a method of fracturing a subterranean formation comprising the steps of: (a) injecting a novel hydraulic fracturing fluid into the formation, the fracturing fluid including a traceable polymer and (b) analyzing a fluid produced from a well to determine if the traceable polymer is present in the fluid.

[0006] In another aspect, the traceable polymer used in the inventive hydraulic fracturing fluid preferably has a weight average molecular weight ( M_w ) in the range of from about 100,000 Da to about 50 million Da and is also preferably from about 10% to about 30% hydrolyzed polyacrylamide. In addition, the molecular weight of the traceable polymer is preferably sufficient such that the traceable polymer also operates as either a friction reducing polymer or a viscosifying polymer in the hydraulic fracturing fluid.

[0007] Further aspects, features, and advantages of the present invention will be apparent to those of ordinary skill in the art upon reading the following Detailed Description of the Preferred Embodiments.

Brief Description of the Drawings

[0008] Fig. 1 is a chart showing the particle size distributions of the traceable polymers produced as described herein in Examples 1 -4.

[0009] Fig. 2 is a chart showing the molecular weight distributions of the traceable polymers produced as described herein in Examples 1 -4.

Detailed Description of the Preferred Embodiments

[0010] The present invention provides a method and hydraulic fracturing composition for fracturing a subterranean formation. The inventive method and hydraulic fracturing composition can be used for performing either single or multistage hydraulic fracturing operations.

[0011] The inventive hydraulic fracturing composition comprises one or more traceable polymers. In the inventive fracturing method, the inventive fracturing fluid is injected into a subterranean formation and, subsequently, the fluid produced from a well associated with the formation is analyzed to determine if the traceable polymer(s) is/are present in the production fluid. The well can be any well associated with the formation in question but will preferably be the same well via which the hydraulic fracturing fluid was delivered into the formation.

[0012] The traceable polymer used in the inventive fracturing composition will preferably have a weight average molecular weight ( M_w ) in the range of from about 500 Da to about 50 million Da, or from about 500 to about 5 million Da and more preferably from about 100,000 to about 50 million Da. In addition, the traceable polymer will preferably be from about 0% to about 30% (more preferably from about 10% to about 30% and most preferably from about 15% to about 30%) hydrolyzed polyacrylamide. Moreover, the weight average molecular weight of the traceable polymer within the ranges stated above will preferably be sufficiently high so as to allow the traceable polymer to also optionally operate as either a friction reducing polymer or as a viscosifying polymer in the inventive hydraulic fracturing composition. [0013] In addition to the traceable polymer(s), the inventive hydraulic fracturing composition can also include generally any or all of the other components and materials used in the industry in fracturing fluids. Examples include, but are not limited to, one or more polysaccharide or polyacrylamide viscosifiers (typically 10 - 30 lb/lOOOgal), one or more cross-linkers (typically 1/2 - 1.5 gal/lOOOgal), salt, one or more shale inhibitors (clay stabilizers) (typically 0.2-0.5% by weight), one or more non-emulsifying surfactants, one or more breakers (typically ½ - 10 lb/lOOOgal), a biocidal agent (typically 0.05 - 0.2% by weight), and/or sand or other proppant material.

[0014] By way of example, but not by way of limitation, each traceable polymer used in the inventive hydraulic fracturing fluid can be a homo-polymer, copolymer, or terpolymer of: acrylamide; acrylic acid; 2-acrylamido-2-methylpropane sulfonate (AMPS); vinyl sulfonate; allyl vinyl sulfonate; maleic anhydride; tumeric acid; diallyl dimethyl ammonium chloride (DADMAC); vinyl benzyl chloride; vinyl benzyl boronate; vinyl imidazole; vinyl trialkyl silane; 4-acetocy styrene; 9-vinyl anthracene; sodium styrene sulphonate; (3-Acrylamidopropyl) trimethylammonium chloride solution (APTAC); 3-Methacrylamido-N, N, N-trimethlpropane-l-aminium chloride (MAPTAC); 2-Dimethylaminoethyl acrylate (ADAME); N, N, Dimethylaminoethyl methacrylate (MADAME); or a combination thereof.

[0015] Also by way of example, but not by way of limitation, the traceable polymer will further preferably include one or more traceable tag constituents selected from: hypophosphite; phosphonates of acrylamide; at least one boron atom; borax; at least one phosphorus atom; at least one silicone atom; at least one germanium atom; vinyl imidazole; a group comprising at least 2 conjugated aromatic rings, boronate groups, or boric groups; 8-aminopyrene-l,3,6-trisulfonic acid; Rhodamine 6G; or (C-21 10 Celltracker blue CMA.

[0016] An example of one procedure for adding a traceable tag to a base polymer involves reacting phosphorous acid with the base polymer to add a phosphonate moiety to at least one side chain group of the base polymer. In this procedure, the phosphorous acid will most preferably be reacted with the base polymer at a temperature of about 65° C.

[0017] The following reaction formula illustrates the production of a preferred base polymer from acrylamide, as well as the addition of a traceable tag to a side chain of the base polymer in accordance with the procedure just described:

wherein n is a value in the range of from about 7 to about 69,000. In the polymeric structure, "m" is associated with the degree of hydrolysis (preferably 15 - 30%). For example, if the degree of hydrolysis is 20% then, preferably, m is a value of from 1.4 to 13800 and n is a value of from 5.6 to 55200.

[0018] In contrast, the following reaction formula illustrates the preparation of a preferred polymer wherein the traceable tag is incorporated in the polymer backbone structure

[0019] In addition to allowing the traceable polymers employed in the inventive hydraulic fracturing composition to be detected, quantified, and analyzed, the traceable tag constituents added to these polymers also provide increased shear resistance. Thus, as compared to other friction reducing or viscosifying polymers used in hydraulic fracturing compositions, the traceable polymers used in the inventive composition are less susceptible to shearing and degradation during high-pressure fracture injection procedures.

[0020] In performing the second step of the inventive hydraulic fracturing procedure wherein the fluid produced from the well is analyzed to determine if the traceable polymer(s) is/are present in the fluid, the tags included in the traceable polymers of the present invention allow the use of simple, yet accurate, analytical techniques, some of which can be readily implemented in the field.

[0021] Examples of procedures preferred for use in analyzing the produced fluid for the presence of the traceable polymer(s) include but are not limited to titration, fluorescence, UV-visible spectroscopy, or inductively coupled plasma mass spectrometry. Such techniques will indicate both the presence and the concentration of the traceable polymer in the produced fluid.

[0022] The inventive method and composition for hydraulic fracturing can be used alone or in combination with microseismic tests and/or other analytical procedures to determine whether production is occurring from one or multiple fractured zones in a subterranean formation. In addition, by using different traceable polymers in the various individual stages of a staged fracturing procedure, and/or by using traceable polymers in some stages but not in others, the inventive fracturing procedure allows the operator to determine (a) which of the fracturing stages are producing and which are not and (b) the quantitative and comparative rates of production from the various fractured stages.

[0023] Also, as an additional benefit of the inventive hydraulic fracturing method, the traceable polymers used in the inventive fracturing composition can aid in the identification of the source of any leakage which may find its way into an aquifer in the vicinity of the well or which may cause other contamination problems.

[0024] The following Examples are intended to illustrate, but in no way limit, the present invention.

EXAMPLE 1

[0025] Into a round bottomed flask equipped with reflux condenser, nitrogen inlet, temperature probe, and stirrer, there were charged 199.3 g of deionized water and 2.07 g of high molecular weight polyacrylamide (PAM) (Kemira Superfloc A- 130 PWG). While introducing nitrogen into the flask, the temperature was increased to 68°C. Then, 20.0 ml of a 1.00% phosphorous acid solution was added. The mixture was stirred for two hours at this temperature. The resulting polymer solution was then cooled to room temperature, dried and collected.

EXAMPLE 2

[0026] Into a round bottomed flask equipped with an addition funnel, nitrogen inlet, temperature probe, and stirrer, there were charged 340 g deionized water, 8.2g acrylic acid, 24.4g acrylamide, and 6mg of iron(II)sulfate heptahydrate. This mixture was stirred and degassed for 1 hour at room temperature. A 0.03wt % solution of sodium persulfate was added dropwise. When a change in temperature of 6°C was observed 16mg of sodium hypophosphite was added. The reaction was allowed to proceed for two hours upon which time 9. l g of 50% sodium hydroxide was added. EXAMPLE 3

[0027] Into a round bottomed flask equipped with an addition funnel, nitrogen inlet, temperature probe, and stirrer, there were charged 180 g deionized water, 4.0g acrylic acid, 16.0g acrylamide, 0.21 g styrene-4-sulfonic acid sodium salt, and 3mg of iron(II)sulfate heptahydrate. This mixture was stirred and degassed for 1 hour at room temperature. 10.0 ml of a 0.10 wt % solution of sodium persulfate was added dropwise. The reaction was allowed to proceed for three hours upon which time 4.4g of 50% sodium hydroxide was added.

EXAMPLE 4

[0028] Into a round bottomed flask equipped with an addition funnel, nitrogen inlet, temperature probe, and stirrer, there were charged 160 g deionized water, 6.0g acrylic acid, 18.0g acrylamide, 0.24g 4-vinylphenyl boronic acid, and 6mg of iron(II)sulfate heptahydrate. This mixture was stirred and degassed for 1 hour at room temperature. 15.0 ml of a 0.10 wt % solution of sodium persulfate was added dropwise. The reaction was allowed to proceed for three hours upon which time 7. lg of 50% sodium hydroxide was added.

EXAMPLE 5

Molecular Weight Determination

[0029] All polymer samples were dried via lipholizer prior to use. Deionized (DI) water was filtered through a 0.45 μιη membrane, and used to wash 50-mL centrifuge tubes. Next, each tube was filled with 30 g of filtered DI water, and 0.09 g polymer was added. The tubes were sealed and agitated with a shaker table for 3 days, upon which time the polymers had dissolved.

[0030] Cuvettes were rinsed with filtered DI water, filled with the polymer solutions, and analyzed with a Malvern Zetasizer to determine the molecular size distribution. The hydrodynamic diameters of the polymers were used to calculate approximate number average ( M_n ) and weight average (M_w ) molecular weights. The size distributions are shown in Figure 1 , the molecular weight distributions in Figure 2, and the results are summarized in Table 1. Table 1. Molecular wei ht avera es for the ol mers in examples 1-4

EXAMPLE 6

[0031] A first zone of a horizontal oil well is isolated and fractured by injecting into the first zone, under pressure, a hydraulic fracturing fluid comprised of water, a shale stabilizer, a scale inhibitor, and a biocide, and 100-5000 ppm of the traceable polymer produced in Example 1.

[0032] A second zone of the horizontal well is then isolated and fractured by injecting into the second zone, under pressure, a hydraulic fracturing fluid comprised of water, a shale stabilizer, a scale inhibitor, and a biocide, and 100-5000 ppm of the traceable polymer produced in Example 2.

[0033] A third zone of the horizontal well is then isolated and fractured by injecting into the third zone, under pressure, a hydraulic fracturing fluid comprised of water, a shale stabilizer, a scale inhibitor, and a biocide, and 100-5000 ppm of the traceable polymer produced in Example 3.

[0034] A fourth zone of the horizontal well is then isolated and fractured by injecting into the fourth zone, under pressure, a hydraulic fracturing fluid comprised of water, a shale stabilizer, a scale inhibitor, and a biocide, and 100-5000 of the traceable polymer produced in Example 4.

[0035] After the fracturing operations are completed and fluid production from the well begins, samples of the fluid produced from the well are obtained periodically and analyzed using an ICP-OES. This analysis provides a positive indication for each of the traceable polymers which is present in the sample and provides the concentration of the traceable polymer in the sample.

[0036] A positive result for any one of the traceable polymers indicates that fluid is being produced from the zone into which the polymer was injected.

* * * *

[0037] Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within this invention as defined by the claims.

Claims

Claims What is claimed is:

1. A method of fracturing a subterranean formation comprising the steps of:

(a) injecting a hydraulic fracturing fluid into said subterranean formation, said fracturing fluid including a traceable polymer and

(b) analyzing a fluid produced from a well to determine if said traceable polymer is present in said fluid.

2. The method of claim 1 wherein said hydraulic fracturing fluid is injected into said subterranean formation via said well.

3. The method of claim 1 wherein said traceable polymer has a weight average molecular weight in a range of from about 100,000 Da to about 50 million Da.

4. The method of claim 1 wherein said traceable polymer is from about 15% to about 30% hydrolyzed polyacrylaide.

5. The method of claim 1 wherein said traceable polymer operates as a friction reducing polymer in said hydraulic fracturing fluid.

6. The method of claim 1 wherein said traceable polymer operates as viscosifying polymer in said hydraulic fracturing fluid.

7. The method of claim 1 wherein said traceable polymer is a homo-polymer, copolymer, or terpolymer of: acrylamide; acrylic acid; 2-acrylamido-2-methylpropane sulfonate (AMPS) ; vinyl sulfonate; vinyl allyl sulfonate; maleic anhydride; fumeric acid; diallyl dimethyl ammonium chloride (DADMAC); vinyl benzyl chloride; vinyl benzyl boronate; vinyl imidazole; vinyl trialkyl silane; 4-acetocy styrene; 9-vinyl anthracene; sodium styrene sulphonate; (3-Acrylamidopropyl) trimethylammonium chloride solution (APTAC); 3-Methacrylamido-N, N, N-trimethlpropane-l-aminium chloride (MAPTAC); 2-Dimethylaminoethyl acrylate (ADAME); N, N, Dimethylaminoethyl methacrylate (MADAME); or a combination thereof.

8. The method of claim 7 wherein said traceable polymer further includes one or more traceable tag constituents selected from: hypophosphite; phosphonates of acrylamide; at least one boron atom; borax; at least one phosphorus atom; at least one silicone atom; at least one germanium atom; vinyl imidazole; a group comprising at least 2 conjugated aromatic rings, boronate groups, or boric groups; 8-aminopyrene-l,3,6- trisulfonic acid; Rhodamine 6G or C-2110 Celltracker blue CMA.

9. The method of claim 1 wherein said traceable polymer is formed by reacting phosphorous acid with a base polymer to add a phosphonate moiety to at least one side chain group of said base polymer.

10. The method of claim 9 wherein said phosphorous acid is reacted with said base polymer at a temperature of about 65° C.

11. The method of claim 1 wherein said traceable polymer comprises one or more compounds having a formula

wherein: said traceable polymer has a degree of hydrolysis of from 0% to about 30%, n is a value in a range of from about 7 to about 69,000, and "m" is related to said degree of hydrolysis of said traceable polymer such that when said degree of hydrolysis is 20%, then m will be a value of from 1.4 to 13800 and n will be a value of from 5.6 to 55200.

12. The method of claim 1 1 wherein said traceable polymer is formed in accordance with the reaction formula

= 1 - 2 million o

13. The method of claim 1 wherein said traceable polymer comprises one or more compounds having a formula

wherein: said traceable polymer has a degree of hydrolysis of from 0% to 30%, n is a value in a range of from about 7 to about 69,000, and "m" is related to said degree of hydrolysis of said traceable polymer such that when said degree of hydrolysis is 20%, then m will be a value of from 1.4 to 13800 and n will be a value of from 5.6 to 55200.

14. The method of claim 13 wherein said traceable polymer is formed in accordance with the following reaction formula

15. The method of claim 1 wherein said fluid is analyzed in step (b) by titration, fluorescence, UV-visible spectroscopy, or inductively coupled plasma mass spectrometry.

16. The method of claim 15 wherein step (b) of analyzing said fluid produced from said well also provides a concentration of said traceable polymer in said fluid.