PRODUCED WATER BORATE CROSSLINKING COMPOSITIONS AND METHOD OF USE

Abstract

A composition and method for treating a fracturing fluid comprising produced water with high levels of dissolved solids using a polymer crosslinked with a boron compound and a high pH alkylamine buffer. The composition improves the viscosity stability of the fracturing fluid at elevated bottom-hole temperatures, particularly when the fluid has high levels of calcium and magnesium. The composition is particularly useful with polysaccharides, including galactomannan gums, such as guar gum, locust bean gum, and karaya gum, and allows for the use of the preferred boron compound crosslinkers in high total dissolved solids fracturing fluids without the pH destabilization problems encountered with the prior art.

Claims

1. A treatment composition for increasing the viscosity of a fracturing fluid, the composition comprising: a galactomannan polymer; a boron compound capable of crosslinking with the polymer; a pH buffer comprising an amine, wherein the pH buffer capable of maintaining the pH of the composition in the fracturing fluid above 9.0 at temperatures greater than 80° F.; wherein the concentration of pH buffer is between 1 to 20 gpt.

2. The treatment composition of claim 1, wherein said boron compound is a delayed boron crosslinker; wherein said temperature is greater than 220° F.; and wherein said concentration of pH buffer is 8-9 gpt.

3. The treatment composition of claim 1, wherein said boron compound is a delayed boron crosslinker; and wherein the pH buffer is capable of maintaining the pH of the composition in the fracturing fluid above 9.0 at temperatures greater than 240° F.

4. The treatment composition of claim 1, wherein the amount of pH buffer comprising an amine is at least about 3 times the amount of boron compound, by weight.

5. The treatment composition of claim 4, wherein the amount of galactomannan polymer is at least about 3 times the amount of boron compound, by weight.

6. The treatment composition of claim 1, wherein the polymer is guar gum or its derivatives and the boron compound is selected from the group consisting of boric acid, borax, sodium borate, disodium tetraborate, sodium tetraborate, sodium tetraborate decahydrate, amino boric acid, elluite, ulexite, colemanite, probertite, and mixtures thereof.

7. The treatment composition of claim 6, wherein the pH buffer is selected from the group consisting of n-butylamine, diethylenetriamine, diaminobutane, diethyldiamine, diisopropylamine, dodecylamine, ethylamine, ethylenediamine, di-(gamma-aminopropylether), methyleneamine, piperazine, triethylenetetramine, tetraethylenepentamine, triethylamine, amino diols, glycols poly glycols, and mixtures thereof.

8. The treatment composition of claim 1, wherein the fracturing fluid comprises produced water.

9. The treatment composition of claim 8, wherein the fracturing fluid comprises greater than 1,500 ppm total dissolved solids.

10. The treatment composition of claim 8, wherein the fracturing fluid comprises greater than 10,000 ppm total dissolved solids.

11. The treatment composition of claim 8, wherein the fracturing fluid comprises greater than 100,000 ppm total dissolved solids.

12. The treatment composition of claim 8, wherein the fracturing fluid water comprises calcium levels greater than about 500 ppm or magnesium levels greater than about 150 ppm.

13. The treatment composition of claim 12, wherein the polymer is guar gum and the pH buffer is DETA.

14. A fracturing fluid comprising: a liquid comprising greater than 1000 ppm total dissolved solids; a polymer soluble in the liquid; a boron crosslinking agent capable of increasing the viscosity of the fracturing fluid by crosslinking with the polymer; a pH buffer comprising an amine, the pH buffer capable of maintaining the pH of the fracturing fluid above 9.0 at temperatures greater than 80° F.

15. The fracturing fluid of claim 14, wherein said boron crosslinking agent is a delayed boron crosslinker; and wherein the pH buffer is capable of maintaining the pH of the fracturing fluid above 9.0 at temperatures greater than 220° F.

16. The fracturing fluid of claim 14, wherein said boron compound is a delayed boron crosslinker; wherein the pH buffer is capable of maintaining the pH of the fracturing fluid above 9.0 at temperatures greater than 240° F.

17. A treatment composition for increasing the viscosity of a fracturing fluid, the composition comprising: a polysaccharide polymer; a delayed boron compound capable of crosslinking with the polymer; an alkylamine pH buffer capable of maintaining the pH of the composition in the fracturing fluid above 9.0 at temperatures greater than 220° F.; wherein the amount of alkylamine is at least about 3 times the amount of boron compound and the amount of polymer is at least about 3 times the amount of boron compound, by weight.

18. The treatment composition of claim 17, wherein the alkylamine pH buffer is capable of maintaining the pH of the composition in the fracturing fluid above 9.0 at temperatures greater than 240° F.

19. A method of treating a fracturing fluid to maintain a stable crosslink viscosity, the method comprising: providing a fracturing fluid comprising produced waters and having a total dissolved solids level greater than 1,500 ppm; adding a polysaccharide to the fracturing fluid to hydrate the polysaccharide; adding an alkylamine pH buffer to the fracturing the fluid, the alkylamine pH buffer being capable of maintaining the fracturing fluid at a pH level greater than 9.0 at temperatures greater than about 220° F.; adding a delayerd boron crosslinking compound to the fracturing fluid; wherein the alkylamine pH buffer is not added until after the polysaccharide has had sufficient time to hydrate in the fracturing fluid.

20. The method of claim 16, wherein the alkylamine pH buffer is capable of maintaining the fracturing fluid at a pH level greater than 9.0 at temperatures greater than about 240° F.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The composition of the invention is further described and explained in relation to the following drawings wherein:

[0016] FIG. 1 is a graphical representation of the viscosity over time for several compositions tested under the temperature at an elevated temperature of 146° F.

[0017] FIG. 2 is a graphical representation of the viscosity over time for several compositions tested at an elevated temperature of 196° F.

[0018] FIG. 3 is a graphical representation of the viscosity over time for several compositions tested at an elevated temperature of 246° F.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] One preferred treatment composition according to the invention comprises a boron-crosslinkable polysaccharide as the polymer, a boron compound crosslinker, and an amine high pH buffer. This preferred composition comprises about 5 to about 100 ppt (pounds per thousand gallons of total fluid, including the fracturing fluid) polysaccharide, between about 0.41 ppt to about 65.22 ppt, and most preferably about 3 ppt to about 11 ppt, of the crosslinking agent, and about 0.25 gpt to 30 gpt amine pH buffer.

[0020] The polysaccharide is preferably in a slurry with a hydrocarbon base, containing about 3-5 pounds of polysaccharide per one gallon of the slurry. The preferred polymer is a galactomannan gum, with guar gum being the most preferred polymer, but other hydratable water-soluble polymer solutions suitable for use in creating a crosslinked fracturing fluids, and particularly any of the hydratable polysaccharides that are capable of gelling water based fluids may be used. Suitable polymers are galactomannan gums, guars, locust bean gum, tara gum, karaya gum, cassia gum, hydroxypropyl guar, carboxymethyl guar, carboxymethylhydroxypropyl guar, carboxymethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylhydroxyethyl cellulose and hydroxyethyl cellulose, and other derivatized guars and cellulose derivatives, and polyvinyl alcohol. The polymer is hydrated with water in the fracturing fluid to form a viscosified or gelled fluid.

[0021] The preferred boron compound crosslinker is boric acid, but other boron containing compounds such as borax, sodium borate, disodium tetraborate, sodium tetraborate, sodium tetraborate decahydrate, amino boric acid, elluite, ulexite, colemanite, probertite, and mixes thereof may be used. Additionally, other non-boron crosslinking agents may be used, but the combination of sufficient viscosity and improved stability achieved with boron compound crosslinkers makes them particularly suitable for use in compositions according to the invention. DETA is the preferred amine pH buffer, but other alkylamines may also be used alone or may be used in combination with DETA. Other basic organic compounds comprising amines (including akyl amines, aryl amines, poly amines, and cyclo amines, and may be primary, secondary, or tertiary amines) may also be used as an amine high pH buffer. These basic compounds yield a pH greater than about 8.0 when dissolved in water, preferably greater than about 10.0, and most preferably yield a pH in the range of 12-13. Examples of such compounds include n-butylamine, diethylenetriamine (DETA), diaminobutane, diethyldiamine, diisopropylamine, dodecylamine, ethylamine, ethylenediamine, di-(gamma-aminopropylether), methyleneamine, piperazine, triethylenetetramine, tetraethylenepentamine, triethylamine, and amino diols, glycols and poly glycols. These basic compounds comprising amines do not have the hydroxide or carbonate radicals common in most high pH buffers (such as sodium hydroxide or potassium carbonate) which precipitate with high levels of hardness (such as calcium and magnesium), thereby reducing the buffering effect. The reaction of the preferred amine pH buffer, DETA, with magnesium and calcium is minimal. As such, the use of these amine pH buffers, such as DETA, are useful in mitigating precipitating reactions with water hardness, such as calcium and magnesium, and are more effective in maintaining a stable pH in high hardness or high TDS waters such as hard fresh waters, produced waters and mixtures thereof.

[0022] According to another embodiment, the composition also comprises a secondary alkaline pH buffer or pH modifier. The secondary pH buffer or modifier is preferably a strongly alkaline hydroxide and/or carbonate compound, such as potassium hydroxide, sodium hydroxide, ammonium hydroxide, potassium carbonate, or mixtures thereof. Although some precipitation may occur when using such secondary pH buffers with high TDS, and particularly high calcium and magnesium levels, the addition of the amine pH buffer may inhibit the reaction that results in the precipitation. The addition of a secondary pH buffer is optional and is not required. When added to the fracturing fluid, the composition according to this embodiment preferably comprises about 4.0 to about 6.0 gpt polysaccharide slurry (containing about 3-5 lbs. of polymer per gallon of slurry), about 1.5 to about 4.0 gpt crosslinking agent-secondary pH buffer solution, and about 0.5 to about 5.0 gpt amine pH buffer.

[0023] Other additives typically used in fracturing fluids, such as biocides, breakers, clay control additives, scale inhibitors, surfactants, water recovery agents, polymer hydration enhancers, high temperature gel stabilizers such as sodium and or ammonium thiosulfate, etc., and proppants may also be used. It is preferred to use 0.1-2.0 gpt biocide and 0.04 to 0.06 gpt low pH buffer (an 80% acetic acid solution is preferred) with the compositions according to the invention. The addition of an acidic low pH buffer may aid in hydration of the polymer, which occurs best at neutral to acidic conditions, so it is preferred to add the low pH buffer with, or near the same time as, the polymer. Although the amount of low pH buffer added is typically not enough to significantly drop the pH level of the fluid, in the tests discussed below, the 80% acetic acid solution was added with the biocide, polymer (a guar and oil slurry), and produced water, which resulted in a pH of 7.05. Prior to addition of the 80% acetic acid solution, the pH of the other components was 7.42.

[0024] These embodiments are preferably used with fracturing fluids having TDS levels in the range of about 1,500 ppm to 400,000 ppm and most preferably in the range of about 5,000 ppm to 200,000 ppm or in waters where the precipitation of water hardness (such as from calcium or magnesium) significantly reduce the stability of the boron crosslink due to the precipitation of commonly used high pH buffers such as hydroxide and/or carbonate based buffers. Such fracturing fluids preferably contain calcium levels in excess of about 500 ppm and/or magnesium levels in excess of about 150 ppm. The required pH level to maintain a stable crosslink between the preferred guar gum polymer and boron crosslinker can vary depending on the temperature, level of TDS, and other factors, but a pH of between 9.0 and 12.0 is preferred. To achieve these pH levels and maintain a stable level at elevated bottom hole temperatures with high TDS fluids, it is preferred that about 0.41 ppt to about 65.22 ppt, and most preferably about 3 ppt to about 11 ppt, of the crosslinking agent is used. When boric acid is used as the crosslinking agent, the preferred amount of boric acid used is about 4 ppt to about 11 ppt, and most preferably from about 4.4 ppt to about 10 ppt. Most preferably, the concentration of amine pH buffer used is about 0.5 gpt to about 10 gpt. It is also preferred that about 5 ppt to about 100 ppt polymer is used. Most preferably, the concentration of polymer used is about 10 ppt to about 50 ppt. The compositions of the invention preferably have certain ratios of amine pH buffer to crosslinker and of polymer to crosslinker to achieve stable crosslinking in high TDS/hardness conditions at elevated bottom-hole temperatures. Preferably, around 0.5 to 300 times as much amine pH buffer (by weight) is used relative to the amount of crosslinking agent used. Most preferably, the amount of amine pH buffer (by weight) used is around 3 to 10 times the amount of the crosslinking agent. It is also preferred that 0.15 to 200 times as much polymer (by weight) is used relative to the amount of crosslinking agent used. Most preferably, the amount of polymer (by weight) used is around 1 to 10 times the amount of crosslinking agents.

[0025] According to a preferred embodiment for using the preferred composition according to the invention, the polymer is first added to the fracturing fluid, which contains water sources with high levels of TDS, such as produced waters or mixtures of produced waters and fresh waters, to hydrate the polymer and form a gel. The preferred polymer is guar gum. Preferably, the fracturing fluid has a TDS level greater than 1,500 ppm and most preferably greater than 10,000 ppm, with calcium levels greater than 500 ppm and/or magnesium levels greater than 150 ppm. The compositions according to the invention are particularly well suited for use with such fracturing fluids, but the compositions may also be used with fracturing fluids containing other levels of TDS, and specifically calcium and/or magnesium levels which precipitate with conventional hydroxide and/or carbonate buffers. Then a crosslinking agent, amine pH buffer, and optionally a secondary pH buffer are added to the fracturing fluid containing the hydrated polymer. The crosslinking agent and amine pH buffer may be pre-mixed in a solution prior to adding to the fracturing fluid, with a secondary pH buffer and/or additional amine pH buffer (which may further stabilize the crosslinked fluid) optionally added separately. Alternatively, the crosslinking agent and secondary pH buffer may be pre-mixed in a solution prior to adding to the fracturing fluid, with the amine pH buffer added separately. As another alternative, the crosslinking agent, amine pH buffer, and secondary pH buffer (if used) may all be added to the fracturing fluid separately. Water and other agents, such as freeze point depressors, may also be mixed with any of these components or may added to these solutions prior to adding to the fracturing fluid.

[0026] When pre-mixed, the crosslinker-amine buffer solution preferably comprises between 2% to 50% by weight of a crosslinking agent, which is preferably a boron compound such as boric acid, and between 1% to 70% by weight of an amine high pH buffer, although this percentage could be as high as 95% by weight when a pure form of an amine high pH buffer (such as pure DETA) is used. Most preferably, the crosslinker-buffer solution comprises between 8%-10% by weight of a cross-linking agent and around 48% to 52% by weight of an amine pH buffer. The amounts of crosslinker and high pH buffer(s) used to achieve the desired crosslinked viscosity in the resulting fracturing fluid will vary depending on the hardness of the water and bottom-hole temperature, as will be apparent to those of skill in the art.

[0027] When a secondary pH buffer or modifier, such as potassium hydroxide, sodium hydroxide, ammonium hydroxide, potassium carbonate, or mixtures thereof is used, the crosslinker-buffer solution preferably has between 2% to 30% by weight of a crosslinking agent, 1% to 70% by weight of an amine pH buffer (although this percentage be as high as 90% by weight when a pure form of an amine high pH buffer, such as pure DETA, is used), and 0.1% to 50% by weight (total) of one or more secondary pH buffers or modifiers. Alternatively, the crosslinking agent and the secondary pH buffer may be mixed into a solution that is subsequently mixed with the alkylamine buffer either prior to addition to the fracturing fluid containing the hydrated polymer or as components added separately to the fracturing fluid containing the hydrated polymer. Plexbor 101, commercially available from Solvay USA Inc. (formerly Chemplex Advanced Materials, LLC), is a preferred crosslinking agent-secondary buffer solution, containing boric acid pre-mixed with potassium hydroxide, and water. When using Plexbor or a similar pre-mixed crosslinker-secondary buffer solution, preferably about 0.25 gpt to about 20 gpt, and more preferably about 0.25 gpt to about 10 gpt is used. The amounts of crosslinker, amine pH buffer(s), and secondary pH buffer(s) (if any) used to achieve the desired crosslinked viscosity in the resulting fracturing fluid will vary depending on the hardness of the water and bottom-hole temperature, as will be apparent to those of skill in the art.

[0028] Adding the polymer to the fracturing fluid first and then adding the crosslinker-buffer solution (either with or without a second pH buffer) has the advantage of allowing the polymer to be hydrated by the fracturing fluid to form a gel. The polymer will not hydrate or will be delayed in hydration in the presence of a boron crosslinking agent at an alkaline pH, so it is best to avoid adding the alkylamine pH buffer (and any secondary high pH buffer or modifier) until after the polymer has hydrated. Although it is preferred to pre-mix the crosslinker-buffer solution and add it to the fracturing fluid after the polymer has hydrated, a crosslinking agent that crosslinks at an alkaline pH could be added to the fracturing fluid at the same time as the polymer, provided the overall pH of the fluid is near neutral or acidic to promote hydration, and the amine buffer and any optional secondary pH buffer or modifier added later. The order of addition of the components to the fracturing fluid is not critical provided that the polymer is hydrated before being introduced to the crosslinker at a pH level that would hinder hydration.

[0029] Several treatment compositions containing various concentrations of the preferred components (guar, boric acid, and DETA) were prepared and tested for viscosity in timed intervals over 60 minutes. Table 1 below shows the components in the compositions tested in gpt (gallons per thousand gallons of fluid, including the fracturing fluid). A produced water sample was used as the fracturing fluid in each test. Water analysis of the produced water indicated it had a specific gravity of 1.080, a pH of 7.12, no H.sub.2S was detected, and a total dissolved solids of 109,534 mg/l. The water analysis data for specific dissolved minerals in the produced water are shown in Table 2.

TABLE-US-00001 TABLE 1 Guar Boric Acid Low pH Test Slurry & Secondary pH DETA Biocide Hydration No. (gpt) Buffer Solution (gpt) (gpt) (gpt) Enhancer (gpt) 1 5 2 1 0.5 0.05 2 5 2 2 0.5 0.05 3 5 2.5 2 0.5 0.05 4 5 2.5 2.5 0.5 0.05 5 5 3 2.5 0.5 0.05 6 5 2.5 3 0.5 0.05

TABLE-US-00002 TABLE 2 Mineral Component Amount Measured (mg/L) Sodium (calculated) 38,269 Calcium 2,800 Magnesium 972 Iron 10 Chloride 66,310 Sulfate 320 Bicarbonate 854 TDS (Total Dissolved Solids) 109,534

[0030] In these tests, a guar slurry was first added to the produced waters and was blended for 60 minutes to allow the guar to hydrate and form a gel. Then the boric acid and secondary pH buffer solution and DETA were simultaneously added to the produced waters containing the hydrated guar and the entire mixture blended for 30 seconds or until the fluid crosslinked. Once all the components were added, the fluid was then placed in a high temperature high pressure (HTHP) viscometer and the temperature increased from ambient temperature to 146° F. in the first fifteen minutes and held constant at 146° F. for the remainder of the test. This simulates use of the composition in a typical downhole environment, although the compositions according to the invention are useful over a wider temperature range from about 80° F. to about 250° F., e.g., greater than about 220° F. or even greater than about 240° F. The biocide and hydration enhancer were added to the produced waters with the guar slurry, as it is generally preferred to add these additives to the fracturing fluid at an early stage of the process, but the timing and sequence of addition of these optional additives is not critical to the functioning of the compositions according to the invention.

[0031] The guar slurry used in these tests comprises guar suspended in a semi-synthetic oil at a concentration of four pounds of guar per gallon of slurry. This slurry is commercially available as Plexgel 907LEB from Solvay USA Inc. (formerly Chemplex Advanced Materials, LLC). When the slurry is added to the produced water, it is hydrated and forms a viscous gel. The crosslinking agent used in these tests is a boric acid pre-mixed with a secondary pH buffer, potassium hydroxide, and water. This solution is commercially available as Plexbor 101 from Solvay USA Inc. (formerly Chemplex Advanced Materials, LLC). The biocide and hydration enhancer used are commercially available as Plexicide 24L and Acetiplex 80 (and 80% acetic acid solution), respectively, from Solvay USA Inc. (formerly Chemplex Advanced Materials, LLC). The biocide and hydration enhancer are usually helpful additives for fracturing operations, but are not necessary to achieve stable crosslinking in the presence of high TDS levels at bottom hole temperatures.

[0032] Table 3 below shows the viscosity in centipoise at 40/sec for each of the compositions tested at five minute intervals over the 60 minute period. FIG. 1 shows the viscosity over the 60 minute test period in graphical form.

TABLE-US-00003 TABLE 3 Test Test Test Test Test Test Time Temp. 1 2 3 4 5 6 (min.) (° F.) (cp) (cp) (cp) (cp) (cp) (cp) 5 120 547 609 622 669 618 495 10 143 394 490 495 676 595 600 15 146 391 544 513 637 528 611 20 146 348 516 495 648 489 547 25 146 316 505 513 588 432 515 30 146 287 487 507 661 427 552 35 146 251 480 515 618 419 566 40 146 224 471 507 611 425 536 45 146 217 465 495 627 438 555 50 146 196 468 483 606 436 566 55 146 168 465 489 621 463 587 60 146 163 465 521 613 430 560

[0033] The viscosity measurements indicate the stability of the crosslink between the guar and boron from the boric acid in the presence of high TDS, including high levels of both calcium and magnesium, at an elevated temperature of 146° F. with the use of DETA as a high pH amine buffer. Whereas if the pH does not remain greater than about 9.0 at a bottom-hole test temperature of 146° F., the crosslinking would be reversed (uncrosslink) and the viscosity would drop to less than 50 cp. If the pH remains greater than about 9.0 under the same conditions, the crosslinking is stable and the viscosity will remain at an acceptably high level. It is preferred that at a given polymer loading, the crosslink viscosity be optimized with respect to viscosity which results when proper dosages of boron crosslinkers and stable high pH levels are achieved and maintained through the duration of the test and fracture treatment at the bottom-hole temperature. Typical optimized crosslink viscosity levels from Table 3 ranged from about 430 cp to about 560 cp at 60 minutes at 146 F and are considered acceptable for fracturing operations, while levels less than 200 cp are not generally considered ideal. There are some fluctuations in the viscosity readings, which are to be expected as the composition continues to be mixed together in the produced water as it was blended. As demonstrated by the results in Table 3 and as illustrated in FIG. 1, the readings for Examples 2-6 show stable viscosity levels indicating stable crosslinking and range from an initial viscosity of 669 cp to 430 cp at 60 minutes. Only Test 1 indicated unstable crosslinking by a significant decline in viscosity level from an initial reading of 547 cp to a final 60 minute reading of 163 cp. The composition used in Test 1 had the least amount of DETA, only 1 gpt, compared to 2 to 3 gpt in the other test compositions.

[0034] The concentrations of DETA and boric acid in Test 1 were 1 gpt and 2 gpt of the overall fluid (including the produced water), respectively, which is below the preferred ratio of the amount of DETA which is 3 times (or more) than the boric acid (by weight) for compositions according to the invention. The amounts of DETA and boric acid in each of Tests 2-6 are within the preferred ratio for an optimized and stable boron crosslink at 146° F. according to the invention. Tests 4 and 6 had the highest viscosity readings. The amounts of DETA and Plexbor 101 in Test 4 were 2.5 gpt and 2.5 gpt of the overall fluid (including the produced water), respectively. Additionally, the amount of Plexgel 907LEB in Test 4 was 5 gpt or 20 ppt guar polymer. The amounts of DETA and Plexbor 101 in Test 6 were 3 gpt and 2.5 gpt of the overall fluid (including the produced water), respectively. Additionally, the amount of Plexgel 907LEB in Test 6 was 5 gpt or 20 ppt guar polymer. These tests demonstrate that compositions having the preferred relative amounts of polymer, crosslinking agent, and pH buffer according to the invention are capable of maintaining a stable pH level, and stable viscosity level, at elevated temperatures in the presence high total dissolved solids in the fracturing fluid.

[0035] Another set of tests were run with a different produced water sample and at a temperature of 196° F. Table 4 below shows the components in the compositions tested in gpt (gallons per thousand gallons of fluid, including the fracturing fluid). Water analysis of the produced water used in these tests indicated it had a specific gravity of 1.080, a pH of 6.17, no H.sub.2S was detected, and a total dissolved solids of 112,682 mg/l. The water analysis data for specific dissolved minerals in the produced water are shown in Table 5.

TABLE-US-00004 TABLE 4 Guar Boric Acid Test Slurry & secondary pH DETA Biocide Low pH Hydration No. (gpt) Buffer Solution (gpt) (gpt) (gpt) Enhancer (gpt) 7 7.5 4 5 0.5 0.05 8 7.5 4 4 0.5 0.05 9 7.5 4 3.5 0.5 0.05 10 7.5 4 3 0.5 0.05 11 7.5 3.5 3.5 0.5 0.05

TABLE-US-00005 TABLE 5 Mineral Component Amount Measured (mg/L) Sodium (calculated) 39,629 Calcium 1,920 Magnesium 1,567 Iron 25 Chloride 68,792 Sulfate 468 Bicarbonate 305 TDS (Total Dissolved Solids) 112,682

[0036] The guar slurry, biocide, hydration enhancer, crosslinker-buffer solution and amine pH buffer used in these tests are the same as those used for Test Nos. 1-6. The mixing procedures were also the same and the temperature increased from ambient temperature to 196° F. within the first 15 minutes to simulate bottom-hole temperatures. Table 6 below shows the viscosity in centipoise at 40/sec for each of the compositions tested at five minute intervals over the 60 minute period as measured on a high temperature high pressure (HTHP) viscometer. FIG. 2 shows the viscosity over the 60 minute test period in graphical form.

TABLE-US-00006 TABLE 6 Test Test Test Test Test Time Temp. 7 8 9 10 11 (min.) (° F.) (cp) (cp) (cp) (cp) (cp) 5 165 1120 961 862 837 818 10 192 850 780 821 677 718 15 196 733 740 735 675 711 20 196 718 760 708 630 696 25 196 695 708 679 609 684 30 196 662 708 707 609 660 35 196 695 704 679 600 656 40 196 678 701 664 606 675 45 196 669 701 643 660 660 50 196 660 698 671 629 672 55 196 654 692 678 587 665 60 196 683 682 701 635 638

[0037] The viscosity measurements indicate the stability of the crosslink between the guar and boron from the boric acid in the presence of high TDS, including high levels of both calcium and magnesium, at an elevated temperature of 196° F. with the use of DETA as a high pH amine buffer. The concentration of DETA used in each of these tests was at least 3.0 gpt and resulted in stable crosslinking, demonstrated by stable viscosity, at 196° F.

[0038] Further set of tests were run with a different produced water sample and at a temperature of 246° F. Table 7 below shows the components in the compositions tested in gpt (gallons per thousand gallons of fluid, including the fracturing fluid). Water analysis of the produced water used in these tests indicated it had a specific gravity of 1.080, a pH of 6.71, no H.sub.2S was detected, and a total dissolved solids of 112,688 mg/l. The water analysis data for specific dissolved minerals in the produced water are shown in Table 8.

TABLE-US-00007 TABLE 7 Delayed High Low pH Guar Boron Temp Gel Hydration Test Slurry Crosslinker DETA Stabilizer Biocide Enhancer No. (gpt) (gpt) (gpt) (gpt) (gpt) (gpt) 12 10 8 8 0 0.5 0.05 13 10 8 9 0 0.5 0.05 14 10 8 9 2.5 0.5 0.05 15 10 8 9 5 0.5 0.05 16 10 8 9 10 0.5 0.05

TABLE-US-00008 TABLE 8 Mineral Component Amount Measured (mg/L) Sodium (calculated) 39609 Calcium 1920 Magnesium 1567 Iron 25 Chloride 68792 Sulfate 469 Bicarbonate 305 TDS (Total Dissolved Solids) 112688

[0039] The guar slurry, biocide, hydration enhancer, and amine pH buffer used in these tests are the same as those used for Test Nos. 1-11. In addition a delayed boron crosslinker (boron salt suspension) and high temperature gel stabilizer (thiosulfate base) were also used. The mixing procedures were also the same and the temperature increased from ambient temperature to 246° F. within the first 15 minutes to simulate bottom-hole temperatures. Table 9 below shows the viscosity in centipoise at 40/sec for each of the compositions tested at five minute intervals over the 60 minute period as measured on a high temperature high pressure (HTHP) viscometer. FIG. 3 shows the viscosity over the 60 minute test period in graphical form.

TABLE-US-00009 TABLE 9 Test Test Test Test Test TIME TEMP 12 13 14 15 16 (min) (° F.) (cp) (cp) (cp) (cp) (cp) 5 210 930 1248 478 556 841 10 245 872 833 1025 750 550 15 246 699 717 781 702 501 20 246 762 789 683 913 523 25 246 712 671 532 1070 482 30 246 308 564 453 804 648 35 246 278 492 404 933 611 40 246 242 497 333 601 430 45 246 229 453 296 548 416 50 246 217 418 285 610 428 55 246 214 395 270 535 380 60 246 205 363 262 553 335

[0040] The viscosity measurements indicate the stability of the crosslink between the guar and boron from the delayed boron crosslinker with and without the high temperature gel stabilizer in the presence of high TDS, including high levels of both calcium and magnesium, at an elevated temperature of 246° F. with the use of DETA as a high pH amine buffer. The concentration of DETA used in each of these tests was at least 8.0 gpt and resulted in stable crosslinking, demonstrated by stable viscosity, at 246° F. Further, optimization can be achieved by varying the levels of the delayed crosslinked boron and amine buffer. It is understood by those skilled in the art that the temperature will affect the relative concentration of the amine buffer and boron crosslinker.

[0041] Additional tests were conducted using Plexbor 101 (boric acid and potassium hydroxide pH buffer), the same guar slurry as the other tests, and high TDS produced water (containing high levels of calcium and magnesium) as the fracturing fluid, but this time the DETA was omitted. The produced water samples used in these tests were the same as those used in previous sets of tests. The polymer did not crosslink in these tests, demonstrating that boron crosslinkers and common buffers are not suitable for use with high TDS fracturing fluids without the addition of an amine pH buffer.

[0042] Likewise, additional tests were also conducted using the delayed boron crosslinker and a potassium hydroxide/potassium carbonate pH buffer, the same guar slurry as the other tests, and high TDS produced water (containing high levels of calcium and magnesium) as the fracturing fluid, but this time the DETA was omitted. The produced water samples used in these tests were the same as those used in previous sets of tests. The polymer did not crosslink in these tests, demonstrating that boron crosslinkers and common buffers are not suitable for use with high TDS fracturing fluids without the addition of an amine pH buffer.

[0043] Although test compositions for Test Nos. 2-16 are preferred compositions according to the invention, other compositions may be used within the scope of the invention. Those of ordinary skill in the art will appreciate upon reading this specification, including the examples contained herein, that modifications and alterations to the composition and methodology for using the composition may be made within the scope of the invention and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventor is legally entitled.