Spherical organic nano boron crosslinker with PAMAM core and preparation method thereof, and gel fracturing fluid

Abstract

A spherical organic nano boron crosslinker with a PAMAM core and a preparation method thereof, and a gel fracturing fluid. A chemical structure of the spherical organic nano boron crosslinker is shown as follows: ##STR00001##
In the formula, n=0, 1, 2 or 3; and ##STR00002##

Claims

1. A spherical organic nano boron crosslinker with a polyamidoamine (PAMAM) core, wherein a chemical structure of the spherical organic nano boron crosslinker is shown as follows: ##STR00009## wherein n=0, 1, 2 or 3; and ##STR00010##

2. A method of preparing the spherical organic nano boron crosslinker of claim 1, comprising: (S1) mixing a boride with ethylene glycol followed by refluxing under stirring until no water is generated to obtain a reaction mixture, wherein a molar ratio of the boride to ethylene glycol is 1:(2-10); and cooling the reaction mixture to room temperature to obtain an intermediate A; (S2) subjecting ethylenediamine or a first whole-generation PAMAM as a central core to Michael addition reaction with methyl acrylate to prepare a half-generation PAMAM; (S3) subjecting the half-generation PAMAM and ethylenediamine to an amidation reaction to prepare a second whole-generation PAMAM; and (S4) reacting the second whole-generation PAMAM with the intermediate A followed by treatment with sodium hydroxide to prepare the spherical organic nano boron crosslinker.

3. The method of claim 2, wherein in step (S1), the boride is boric acid or borax.

4. The method of claim 2, wherein in step (S2), a molar ratio of the ethylenediamine or the first whole-generation PAMAM to the methyl acrylate is 1:(8-64).

5. The method of claim 2, wherein in step (S3), a molar ratio of the half-generation PAMAM to the ethylenediamine is 1:(20-50).

6. The method of claim 2, wherein in step (S4), a molar ratio of the second whole-generation PAMAM to the intermediate A is 1:(4-32).

7. The method of claim 2, wherein in step (S4), the second whole-generation PAMAM is reacted with the intermediate A at 140° C.-150° C. for 3-5 h.

8. The method of claim 7, wherein in step (S4), the second whole-generation PAMAM is reacted with the intermediate A at 150° C. for 4 h.

9. A gel fracturing fluid, comprising: the spherical organic nano boron crosslinker of claim 1.

10. The gel fracturing fluid of claim 9, comprising: 0.4 wt %-0.8 wt % of the spherical organic nano boron crosslinker.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to clearly explain the technical solutions in the embodiments of the present disclosure or the prior art, the drawings that need to be used in the description of the embodiments of the disclosure or the prior art will be briefly described below. Obviously, illustrated in the drawings are merely some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without paying creative effort.

(2) FIG. 1 shows a grain size distribution of PAMAM-1, PAMAM-2, PAMAM-3 and PAMAM-4 spherical organic nano boron crosslinkers;

(3) FIG. 2 shows an infrared spectrum of the PAMAM-1, PAMAM-2, PAMAM-3 and PAMAM-4 spherical organic nano boron crosslinkers;

(4) FIG. 3 shows a rheological curve of a gel fracturing fluid prepared according to Example 1 of the present disclosure;

(5) FIG. 4 shows a rheological curve of a gel fracturing fluid prepared according to Example 2 of the present disclosure;

(6) FIG. 5 shows a rheological curve of a gel fracturing fluid prepared according to Example 3 of the present disclosure;

(7) FIG. 6 shows a rheological curve of a gel fracturing fluid prepared according to Example 4 of the present disclosure;

(8) FIG. 7 shows a rheological curve of a conventional boron-crosslinked guar gum fracturing fluid according to Comparative Example 1 of the present disclosure;

(9) FIG. 8 shows a rheological curve of a conventional boron-crosslinked guar gum fracturing fluid according to Comparative Example 2 of the present disclosure;

(10) FIG. 9 shows a rheological curve of a conventional boron-crosslinked guar gum fracturing fluid according to Comparative Example 3 of the present disclosure; and

(11) FIG. 10 shows a rheological curve of a conventional boron-crosslinked guar gum fracturing fluid according to Comparative Example 4 of the present disclosure;

DETAILED DESCRIPTION OF EMBODIMENTS

(12) This application will be described in detail below with reference to the accompanying drawings and embodiments to describe the technical solutions of this application more clearly and completely. Obviously, provided below are merely some embodiments of the present disclosure, which are not intended to limit the disclosure. Other embodiments obtained by those of the ordinary skill in the art based on the embodiments provided herein without paying any creative effort shall fall within the scope of the present disclosure.

(13) As used herein, the term “PAMAM (polyamidoamine)” refers to a polyamide-amine dendrimer, which not only possesses the common characteristics of dendrimers, but also has desirable thermal stability, water solubility, special viscosity and surface tension.

(14) Unless otherwise specified, the test materials and reagents used in the following embodiments are all commercially available. The experimental methods in the following embodiments are conventional methods unless otherwise specified. For example, the raw materials used in the following embodiments include the following components, but is not limited thereto: boride: boric acid and borax; alkali: 20 wt % sodium hydroxide aqueous solution; clay stabilizer: potassium chloride; bactericide: glutaraldehyde; pH regulator: sodium bicarbonate; guar gum: hydroxypropyl guar gum (guar gums containing a cis-ortho-hydroxyl, such as carboxyl methyl guar gum and carboxylmethyl hydroxypropyl guar gum, and derivatives thereof are also feasible); and gel breaker: ammonium persulfate.

(15) In the following embodiments, the rheological curve of the gel fracturing fluid is measured by a high-temperature and high-pressure HAAKE RS600 rheometer. The viscosity of the gel fracturing fluid after gel breaking and the content of the broken gel residue are measured by the method mentioned in SY/T 5107-2016 “The evaluation measurement for properties of water-based fracturing fluid”.

EXAMPLE 1

Preparation of PAMAM-1 Spherical Organic Nano Boron Crosslinker and Gel Fracturing Fluid Containing the Same

(16) 1. Preparation of PAMAM-1 Spherical Organic Nano Boron Crosslinker

(17) (S1) Preparation of Intermediate A

(18) Boric acid and ethylene glycol were added to a three-necked round-bottomed flask equipped with a water separator and a condensing reflux device and refluxed under magnetic stirring until no water was generated to obtain a reaction mixture, where a molar ratio of boric acid to ethylene glycol was 1:4. The reaction mixture was cooled to room temperature to obtain an intermediate A.

(19) (S2) Preparation of Half-Generation PAMAM

(20) Ethylenediamine and methyl acrylate were slowly added to methanol in an ice-water bath under nitrogen protection and then reacted at room temperature for 24 h, where a molar ratio of ethylenediamine to methyl acrylate was 1:8. After that, the reaction mixture was evaporated under reduced pressure to remove the excess methyl acrylate and solvent to obtain a G0.5 PAMAM with an ester group as the terminal group.

(21) (S3) Preparation of Whole-Generation PAMAM

(22) The G0.5 PAMAM and ethylenediamine were slowly added to methanol in an ice-water bath under nitrogen protection and reacted at room temperature for 24 h, where a molar ratio of the G0.5 PAMAM to ethylenediamine was 1:20. After that, the reaction mixture was evaporated under reduced pressure to remove the excess ethylenediamine and solvent to obtain a G1.0 PAMAM (denoted as PAMAM-1).

(23) (S4) Preparation of Spherical Organic Nano Boron Crosslinker

(24) The PAMAM-1 was reacted with the intermediate A at 150° C. for 4 h, where a molar ratio of the PAMAM-1 to the intermediate A was 1:4, and then the reaction product was treated with a 20 wt % sodium hydroxide solution to produce the PAMAM-1 spherical organic nano boron crosslinker, which was structurally shown as follows:

(25) ##STR00005##

(26) Referring to FIG. 1, it can be observed that the PAMAM-1 spherical organic nano boron crosslinker was nano-sized.

(27) Referring to FIG. 2, it demonstrated that boric acid ester was successfully bound to the PAMAM-1 spherical organic nano boron crosslinker.

(28) 2. Preparation of Gel Fracturing Fluid

(29) (S1) Preparation of 0.2 wt % Guar Gum Base Fluid

(30) 0.2 part by weight of guar gum was slowly added into 99.8 parts by weight of water followed by stirring for 30 min to obtain a guar gum base fluid, which was allowed to stand for swelling.

(31) (S2) After the guar gum was completely swollen, the guar gum base fluid was added with 0.8 wt % of a clay stabilizer, 0.1 wt % of a bactericide and 0.1 wt % of a pH regulator, and then added with 0.4 wt % of the PAMAM-1 spherical organic nano boron crosslinker and evenly mixed to prepare a gel fracturing fluid.

(32) Referring to FIG. 3, it showed that the viscosity of the gel fracturing fluid prepared herein was maintained above 100 mPa.Math.s after sheared at 90° C. and 170 s.sup.−1 for 120 min, indicating that the gel fracturing fluid can be applied to the site construction.

(33) After the gel breaking at 70° C. in the presence of a gel breaker for 4 h, the viscosity of the fracturing fluid and the residue content were measured, and the results were shown in Table 1.

EXAMPLE 2

Preparation of PAMAM-2 Spherical Organic Nano Boron Crosslinker and Gel Fracturing Fluid Containing the Same

(34) 1. Preparation of PAMAM-2 Spherical Organic Nano Boron Crosslinker

(35) (S1) Preparation of Intermediate A

(36) Boric acid and ethylene glycol were added to a three-necked round-bottomed flask equipped with a water separator and a condensing reflux device and refluxed under magnetic stirring until no water was generated to obtain a reaction mixture, where a molar ratio of boric acid to ethylene glycol was 1:4. The reaction mixture was cooled to room temperature to obtain an intermediate A.

(37) (S2) Preparation of Half-Generation PAMAM

(38) The PAMAM-1 prepared in Example 1 and methyl acrylate were slowly added to methanol in an ice-water bath under nitrogen protection and then reacted at room temperature for 36 h, where a molar ratio of the PAMAM-1 to methyl acrylate was 1:16. After that, the reaction mixture was evaporated under reduced pressure to remove the excess methyl acrylate and solvent to obtain a G1.5 PAMAM with an ester group as the terminal group.

(39) (S3) Preparation of Whole-Generation PAMAM

(40) The G1.5 PAMAM and ethylenediamine were slowly added to methanol in an ice-water bath under nitrogen protection and reacted at room temperature for 36 h, where a molar ratio of the G1.5 PAMAM to ethylenediamine was 1:30. After that, the reaction mixture was evaporated under reduced pressure to remove the excess ethylenediamine and solvent to obtain a G2.0 PAMAM (denoted as PAMAM-2).

(41) (S4) Preparation of Spherical Organic Nano Boron Crosslinker

(42) The PAMAM-2 was reacted with the intermediate A at 150° C. for 4 h, where a molar ratio of the PAMAM-2 to the intermediate A was 1:8, and then the reaction product was treated with a 20 wt % sodium hydroxide solution to produce the PAMAM-2 spherical organic nano boron crosslinker, which was structurally shown as follows:

(43) ##STR00006##

(44) Referring to FIG. 1, it can be observed that the PAMAM-2 spherical organic nano boron crosslinker was nano-sized.

(45) Referring to FIG. 2, it demonstrated that boric acid ester was successfully bound to the PAMAM-2 spherical organic nano boron crosslinker.

(46) 2. Preparation of Gel Fracturing Fluid

(47) (S1) Preparation of 0.25 wt % Guar Gum Base Fluid

(48) 0.25 part by weight of guar gum was slowly added into 99.75 parts by weight of water followed by stirring for 30 min to obtain a guar gum base fluid, which was allowed to stand for swelling.

(49) (S2) After the guar gum was completely swollen, the guar gum base fluid was added with 0.8 wt % of a clay stabilizer, 0.1 wt % of a bactericide and 0.1 wt % of a pH regulator, and then added with 0.5 wt % of the PAMAM-2 spherical organic nano boron crosslinker and evenly mixed to prepare a gel fracturing fluid.

(50) Referring to FIG. 4, it showed that the viscosity of the gel fracturing fluid prepared herein was maintained above 100 mPa.Math.s after sheared at 120° C. and 170 s.sup.−1 for 120 min, indicating that the gel fracturing fluid can be applied to the site construction.

(51) After the gel breaking at 70° C. in the presence of a gel breaker for 4 h, the viscosity of the fracturing fluid and the residue content were measured, and the results were shown in Table 1.

EXAMPLE 3

Preparation of PAMAM-3 Spherical Organic Nano Boron Crosslinker and Gel Fracturing Fluid Containing the Same

(52) 1. Preparation of PAMAM-3 Spherical Organic Nano Boron Crosslinker

(53) (S1) Preparation of Intermediate A

(54) Boric acid and ethylene glycol were added to a three-necked round-bottomed flask equipped with a water separator and a condensing reflux device and refluxed under magnetic stirring until no water was generated to obtain a reaction mixture, where a molar ratio of boric acid to ethylene glycol was 1:4. The reaction mixture was cooled to room temperature to obtain an intermediate A.

(55) (S2) Preparation of Half-Generation PAMAM

(56) The PAMAM-2 prepared in Example 2 and methyl acrylate were slowly added to methanol in an ice-water bath under nitrogen protection and then reacted at room temperature for 48 h, where a molar ratio of the PAMAM-2 to methyl acrylate was 1:32. After that, the reaction mixture was evaporated under reduced pressure to remove the excess methyl acrylate and solvent to obtain a G2.5 PAMAM with an ester group as the terminal group.

(57) (S3) Preparation of Whole-Generation PAMAM

(58) The G2.5 PAMAM and ethylenediamine were slowly added to methanol in an ice-water bath under nitrogen protection and reacted at room temperature for 48 h, where a molar ratio of the G2.5 PAMAM to ethylenediamine was 1:40. After that, the reaction mixture was evaporated under reduced pressure to remove the excess ethylenediamine and solvent to obtain a G3.0 PAMAM (denoted as PAMAM-3).

(59) (S4) Preparation of Spherical Organic Nano Boron Crosslinker

(60) The PAMAM-3 was reacted with the intermediate A at 150° C. for 4 h, where a molar ratio of the PAMAM-3 to the intermediate A was 1:4, and then the reaction product was treated with a 20 wt % sodium hydroxide solution to produce the PAMAM-3 spherical organic nano boron crosslinker, which was structurally shown as follows:

(61) ##STR00007##

(62) Referring to FIG. 1, it can be observed that the PAMAM-3 spherical organic nano boron crosslinker is nano-sized.

(63) Referring to FIG. 2, it demonstrated that boric acid ester was successfully bound to the PAMAM-3 spherical organic nano boron crosslinker.

(64) 2. Preparation of Gel Fracturing Fluid

(65) (S1) Preparation of 0.36 wt % Guar Gum Base Fluid

(66) 0.36 part by weight of guar gum was slowly added into 99.64 parts by weight of water followed by stirring for 30 min to obtain a guar gum base fluid, which was allowed to stand for swelling.

(67) (S2) After the guar gum base fluid was completely swollen, the guar gum base fluid was added with 0.8 wt % of a clay stabilizer, 0.1 wt % of a bactericide and 0.1 wt % of a pH regulator, and then added with 0.6 wt % of a PAMAM-3 spherical organic nano boron crosslinker and evenly mixed to prepare a gel fracturing fluid.

(68) Referring to FIG. 5, it showed that the viscosity of the gel fracturing fluid prepared herein is maintained above 70 mPa.Math.s after sheared at 150° C. and 170 s.sup.−1 for 120 min, indicating that the gel fracturing fluid can be applied to the site construction.

(69) After the gel breaking at 70° C. in the presence of a gel breaker for 4 h, the viscosity of the fracturing fluid and the residue content were measured, and the results were shown in Table 1.

EXAMPLE 4

Preparation of PAMAM-4 Spherical Organic Nano Boron Crosslinker and Gel Fracturing Fluid Containing the Same

(70) 1 Preparation of PAMAM-4 Spherical Organic Nano Boron Crosslinker

(71) (S1) Preparation of Intermediate A

(72) Borax and ethylene glycol were added to a three-necked round-bottomed flask equipped with a water separator and a condensing reflux device and refluxed under magnetic stirring until no water was generated to obtain a reaction mixture, where a molar ratio of borax to ethylene glycol was 1:4. The reaction mixture was cooled to room temperature to obtain an intermediate A.

(73) (S2) Preparation of Half-Generation PAMAM

(74) The PAMAM-3 prepared in Example 3 and methyl acrylate were slowly added to methanol in an ice-water bath under nitrogen protection and then reacted at room temperature for 72 h, where a molar ratio of the PAMAM-3 to methyl acrylate was 1:64. After that, the reaction mixture was evaporated under reduced pressure to remove the excess methyl acrylate and solvent to obtain a G3.5 PAMAM with an ester group as the terminal group.

(75) (S3) Preparation of Whole-Generation PAMAM

(76) The G3.5 PAMAM and ethylenediamine were slowly added to methanol in an ice-water bath under nitrogen protection, and reacted at room temperature for 72 h where a molar ratio of the G3.5 PAMAM central cores to ethylenediamine was 1:50. After that, the reaction mixture was evaporated under reduced pressure to remove the excess ethylenediamine and solvent to obtain a G4.0 PAMAM (denoted as PAMAM-4).

(77) (S4) Preparation of Spherical Organic Nano Boron Crosslinker

(78) The PAMAM-4 was reacted with the intermediate A at 150° C. for 4 h, where a molar ratio of the PAMAM-4 to the intermediate A was 1:4, and then the reaction product was treated with a 20 wt % sodium hydroxide solution to produce the PAMAM-4 spherical organic nano boron crosslinker, which was structurally shown as follows:

(79) ##STR00008##

(80) Referring to FIG. 1, it can be observed that the PAMAM-4 spherical organic nano boron crosslinker is nano-sized.

(81) Referring to FIG. 2, it demonstrated that boric acid ester was successfully bound to the PAMAM-4 spherical organic nano boron crosslinker.

(82) 2. Preparation of Gel Fracturing Fluid

(83) (S1) Preparation of 0.5 wt % Guar Gum Base Fluid 0.5 part by weight of guar gum was slowly added into 99.5 parts by weight of water followed by stirring for 30 min to obtain a guar gum base fluid, which was allowed to stand for swelling.

(84) (S2) After the guar gum was completely swollen, the guar gum base fluid was added with 0.8 wt % of a clay stabilizer, 0.1 wt % of a bactericide and 0.1 wt % of a pH regulator, and then added with 0.8 wt % of the PAMAM-4 spherical organic nano boron crosslinker and evenly mixed to prepare a gel fracturing fluid.

(85) Referring to FIG. 6, it showed that the viscosity of the gel fracturing fluid prepared herein was maintained above 60 mPa.Math.s after sheared at 180° C. and 170 s.sup.−1 for 120 min, indicating that the gel fracturing fluid can be applied to the site construction.

(86) After the gel breaking at 70° C. in the presence of a gel breaker for 4 h, the viscosity of the fracturing fluid and the residue content were measured, and the results were shown in Table 1.

Comparative Example 1

Preparation of Conventional Organic Boron Crosslinker and Boron Crosslinked Guar Gum Gel Containing the Same

(87) 1. Preparation of Conventional Organic Boron Crosslinker

(88) Boric acid and ethylene glycol were added to a three-necked round-bottomed flask equipped with a water separator and a condensing reflux device refluxed under magnetic stirring until no water was generated to obtain a reaction mixture, where a molar ratio of boric acid to ethylene glycol was 1:4. The reaction mixture was cooled to room temperature and then treated with a 20 wt % sodium hydroxide solution to obtain a conventional organic boron crosslinker.

(89) 2. Preparation of Conventional Boron Crosslinked Guar Gum Gel

(90) (S1) Preparation of 0.2 wt % Guar Gum Base Fluid

(91) 0.2 part by weight of guar gum was slowly added into 99.8 parts by weight of water followed by stirring for 30 min to obtain a guar gum base fluid, which was allowed to stand for swelling.

(92) (S2) After the guar gum was completely swollen, the guar gum base fluid was added with 0.8 wt % of a clay stabilizer, 0.1 wt % of a bactericide and 0.1 wt % of a pH regulator, and then added with 0.4 wt % of the conventional organic boron crosslinker and evenly mixed to prepare a boron crosslinked guar gum gel.

(93) Referring to FIG. 7, it showed that the viscosity of the boron crosslinked guar gum gel prepared herein was reduced below 50 mPa.Math.s after sheared at 90° C. and 170 s.sup.−1 for 40 min, indicating that the boron crosslinked guar gum gel fails to be applied to the site construction.

(94) After the gel breaking at 70° C. in the presence of a gel breaker for 4 h, the viscosity of the fracturing fluid and the residue content were measured, and the results were shown in Table 1.

Comparative Example 2

Preparation of Conventional Organic Boron Crosslinker and Boron Crosslinked Guar Gum Gel Containing the Same

(95) 1. Preparation of Conventional Organic Boron Crosslinker

(96) Boric acid and ethylene glycol were added to a three-necked round-bottomed flask equipped with a water separator and a condensing reflux device and refluxed under magnetic stirring until no water was generated to obtain a reaction mixture, where a molar ratio of boric acid to ethylene glycol was 1:4. The reaction mixture was cooled to room temperature, and then treated with a 20 wt % of sodium hydroxide solution to obtain a conventional organic boron crosslinker.

(97) 2. Preparation of Conventional Boron Crosslinked Guar Gum Gel

(98) (S1) Preparation of 0.25 wt % Guar Gum Base Fluid

(99) 0.25 part by weight of guar gum was slowly added into 99.75 parts by weight of water followed by stirring for 30 min to obtain a guar gum base fluid, which was allowed to stand for swelling.

(100) (S2) After the guar gum was completely swollen, the guar gum base fluid was added with 0.8 wt % of a clay stabilizer, 0.1 wt % of a bactericide and 0.1 wt % of a pH regulator, and then added with 0.5 wt % of the conventional organic boron crosslinker, and evenly mixed to prepare the boron crosslinked guar gum gel.

(101) Referring to FIG. 8, it showed that the viscosity of the boron crosslinked guar gum gel prepared herein was reduced below 50 mPa.Math.s after sheared at 120° C. and 170 s.sup.−1 for 80 min, indicating that the boron crosslinked guar gum gel fails to be applied to the site construction.

(102) After the gel breaking at 70° C. in the presence of a gel breaker for 4 h, the viscosity of the fracturing fluid and the residue content were measured, and the results were shown in Table 1.

Comparative Example 3

Preparation of Conventional Organic Boron Crosslinker and Boron Crosslinked Guar Gum Gel Containing the Same

(103) 1. Preparation of Conventional Organic Boron Crosslinker

(104) Boric acid and ethylene glycol were added to a three-necked round-bottomed flask equipped with a water separator and a condensing reflux device and refluxed under magnetic stirring until no water was generated to obtain a reaction mixture, where a molar ratio of boric acid to ethylene glycol was 1:4. The reaction mixture was cooled to room temperature, and then treated with a 20 wt % of a sodium hydroxide solution to obtain a conventional organic boron crosslinker.

(105) 2. Preparation of Conventional Boron Crosslinked Guar Gum Gel

(106) (S1) Preparation of 0.36 wt % Guar Gum Base Fluid

(107) 0.36 part by weight of guar gum was slowly added into 99.64 parts by weight of water followed by stirring for 30 min to obtain a guar gum base fluid, which was allowed to stand for swelling.

(108) (S2) After the guar gum was completely swollen, the guar gum base fluid was added with 0.8 wt % of a clay stabilizer, 0.1 wt % of a bactericide and 0.1 wt % of a pH regulator, and then added with 0.6 wt % of the conventional organic boron crosslinker, and evenly mixed to prepare the boron crosslinked guar gum gel.

(109) Referring to FIG. 9, it showed that the viscosity of the boron crosslinked guar gum gel prepared herein is reduced below 50 mPa.Math.s after sheared at 150° C. and 170 s.sup.−1 for 70 min, indicating that the boron crosslinked guar gum gel fails to be applied to the site construction.

(110) After the gel breaking at 70° C. in the presence of a gel breaker for 4 h, the viscosity of the fracturing fluid and the residue content were measured, and the results were shown in Table 1.

Comparative Example 4

Preparation of Conventional Organic Boron Crosslinker and Boron Crosslinked Guar Gum Gel Containing the Same

(111) 1. Preparation of Conventional Organic Boron Crosslinker

(112) Boric acid and ethylene glycol were added to a three-necked round-bottomed flask equipped with a water separator and a condensing reflux device and refluxed under magnetic stirring until no water was generated to obtain a reaction mixture, where a molar ratio of boric acid to ethylene glycol was 1:4. The reaction mixture was cooled to room temperature, and then treated with a 20 wt % of a sodium hydroxide solution to obtain a conventional organic boron crosslinker.

(113) 2. Preparation of Conventional Boron Crosslinked Guar Gum Gel

(114) (S1) Preparation of 0.5 wt % of a Guar Gum Base Fluid

(115) 0.5 part by weight of guar gum was slowly added into 99.5 parts by weight of water followed by stirring for 30 min to obtain a guar gum base fluid, which was allowed to stand for swelling.

(116) (S2) After the guar gum was completely swollen, the guar gum base fluid was added with 0.8 wt % of a clay stabilizer, 0.1 wt % of a bactericide and 0.1 wt % of a pH regulator, and then added with 0.8 wt % of the conventional organic boron crosslinker, and evenly mixed to prepare a boron crosslinked guar gum gel.

(117) Referring to FIG. 10, it showed that the viscosity of the boron crosslinked guar gum gel prepared herein was reduced below 50 mPa.Math.s after sheared at 180° C. and 170 s.sup.−1 for 70 min, indicating that the boron crosslinked guar gum gel fails to be applied to the site construction.

(118) After the gel breaking at 70° C. in the presence of a gel breaker for 4 h, the viscosity of the fracturing fluid and the residue content were measured, and the results were shown in Table 1.

(119) TABLE-US-00001 TABLE 1 Test results of properties of gel fracturing fluid Viscosity after Residue content in Gel fracturing gel breaking gel-breaking fluid fluid (mPa .Math. s) (mg/L) Example 1 1.96 188 Example 2 2.20 250 Example 3 2.21 374 Example 4 3.45 514 Comparative 1.85 184 Example 1 Comparative 2.03 242 Example 2 Comparative 2.25 398 Example 3 Comparative 3.78 496 Example 4

(120) It can be concluded from the data in Table 1 that compared with Comparative Examples 1-4, the gel fracturing fluid prepared in each of Examples 1-4 has similar viscosity and residue content in the gel-breaking fluid after gel breaking. The amount of guar gum is the main factor affecting the viscosity and residue content of the gel-breaking fluid. Under the same amount of guar gum, the temperature resistance of the gel fracturing fluid prepared in each of Examples 1-4 is significantly improved, while the viscosity and residue content of the gel-breaking fluid will not be significantly improved, so as to facilitate the flowback of the gel-breaking fluid.