SELF-HYDRATING, SELF-CROSSLINKING GUAR COMPOSITIONS AND METHODS

Abstract

A self-hydrating, self-crosslinking dry composition is used to prepare a hydrated, crosslinked fracturing fluid upon addition of water, the composition comprising (A) guar powder or a guar derivative powder; (B) crosslinker selected from the group consisting of boric acid, borax, borate ore, boron ore, antimony compounds, aluminum compounds, zirconium compounds, and titanium compounds; and (C) slow dissolving alkaline buffer, wherein the crosslinker (B) is non-encapsulated.

Description

EXAMPLES

The following examples illustrate a few embodiments of the invention and compare the invention to other formulations. All parts and percentages are by weight unless otherwise indicated.

Example 1

A single self-hydrating, self-crosslinking dry package of formulated guar was made by mixing 100 parts guar, 20 parts reagent grade magnesium oxide as slow dissolving high pH buffer, 8 parts orthoboric acid as non-encapsulated crosslinker, and 2.8 parts sulfamic acid as low pH hydration buffer. The dry package hydrated rapidly when added to water and crosslinked to form a gel without the addition of any further ingredients. The guar, referred to herein as Guar 1, was prepared by jetmilling underivatized guar with a final D50% (μm) particle size of 15 and D90% (μm) particle size of 30. The resultant Guar 1 reached a viscosity of 26.8 cP in 1 minute and % hydration of 85 in 1 minute. The viscosities after 1, 2, 3, 4, 5, 10 and 60 minutes are 26.8, 29, 29.8, 30.2, 30.4, 31 and 31.4 cP. Then 1.5 gm of this Guar 1 formulation was added to 250 ml of deionized water in a Waring blender (500 ml jar) and the speed was adjusted to about 2800 rpm. 1.5 gm of formulated guar 1 is added to the blender. A crosslinked gel was successfully formed in about 30 seconds.

Example 2

Example 1 was repeated, except that Guar 2 was used instead of Guar 1. Guar 2 was also an underivatized guar having a molecular weight of 2.32×10⁶, D_50% (μm) particle size 34.77, D_90% (μm) particle size 69.96, viscosity cP at 17.0, 22.4, 25.0, 27.0 28.0, 30.0, and 33.0, respectively, after 1, 2, 3, 4, 5, 10, and 60 minutes, and % hydration of 52, 68, 76, 82, 85, 91, and 100, respectively, after the same time intervals. A weak, but acceptable, gel was formed in about 30 seconds.

Example 3

Four dry formulations, A, B, C, and D, as set forth in Table I, were prepared by mixing the dry components, using either Guar1, Guar2, Guar3, or HPG, respectively. Guar1 and Guar2 were fast acting as described in Examples 1 and 2. HPG was a derivatized guar powder. Guar3 was an underivatized guar with a D_50% (μm) particle size of 48.77, D_90% (μm) particle size 91.44, viscosity cP at 16.4, 26.6, 33.6, 36.4, 39.4, 45.6, & 48.2, respectively, after 1, 2, 3, 4, 5, 10, & 60 minutes, and % hydration of 34, 55, 70, 76, 82, 95 & 100, respectively, after the same time intervals. The crosslinker was unencapsulated orthoboric acid. No encapsulated crosslinker was included. Magchem 30, a technical grade of magnesium oxide from Martin Marietta Magnesia specialties and was used as the slow dissolving high pH buffer in formulations A-D. Formulations A-D were dry blended.

	TABLE I
	Formulation A	Formulation B	Formulation C	Formulation D
Polymer	12 gm of guar1	12 gm of guar2	12 gm of guar3	1.2 gm of HPG
				(d50~55 microns,
				d90~99 microns)
Crosslinker	1 gm of	1 gm of	1 gm of	0.1 gm of
	orthoboric acid	orthoboric acid	orthoboric acid	orthoboric acid
Slow	0.5 gm of	0.5 gm of	0.5 gm of	0.05 gm of
dissolving	Magchem 30	Magchem 30	Magchem 30	Magchem 30
high pH buffer
Low pH acid	0.1 gm of	0.1 gm of	0.1 gm of	0.01 gm of
	fumaric acid	fumaric acid	fumaric acid	fumaric acid

Example 4

1.25 gm of formulation A was added to 250 gm of deionized water in a blender and mixed for 30 seconds at 2800 rpm. This fluid formed a crosslinked gel in about 3 minutes. The pH of the sample was monitored as a function of time with the results set forth in Table II.

	TABLE II
	Time(min)
	1	2	3	4	5
	pH	6.1	7.1	7.9	8.1	8.25

The results of this experiment show that the slow dissolving high pH buffer, Magchem 30, is effective in keeping the pH initially low to allow sufficient hydration and then slowly increases the pH, which activates the crosslinker to form a gel.

Example 5

0.75 gm of formulation A was added to 250 gm of deionized water in a blender and mixed for 30 seconds at 2800 rpm. This fluid formed a crosslinked gel in about 8 minutes, with the results shown in Table III.

	TABLE III
	Time(min)
	1	2	3	4	5	8
pH	5.75	6.8	7.8	8.05	8.25	8.6

Example 6

1.25 gm of formulation B was added to 250 gm of deionized water in a blender and mixed for 30 seconds at 2800 rpm. This fluid formed a crosslinked gel in about 4 minutes. The pH of the sample was monitored as a function of time with the results shown in Table IV.

	TABLE IV
	Time(min)
	1	2	3	4	5
	pH	5.9	6.95	7.7	8	8.15

Example 7

0.75 gm of formulation b was added to 250 gm of deionized water in a blender and mixed for 30 seconds at 2800 rpm. This fluid formed a crosslinked gel in about 8 minutes with the results shown in Table V.

	TABLE V
	Time(min)
	1	2	3	4	5	8
pH	6.25	7.2	7.65	8.05	8.2	8.5

Example 8

1.25 gm of formulation C was added to 250 gm of deionized water in a blender and mixed for 30 seconds at 2800 rpm. This fluid formed a crosslinked gel in about 4 minutes. The pH of the sample was monitored as a function of time, with the results shown in Table VI.

	TABLE VI
	Time(min)
	1	2	3	4	5
	pH	6.25	7.6	8.05	8.35	8.5

Example 9

0.75 gm of formulation C was added to 250 gm of deionized water in a blender and mixed for 30 seconds at 2800 rpm. This fluid formed a crosslinked gel in about 7-8 minutes, with the results shown in Table VII.

	TABLE VII
	Time(min)
	1	2	3	4	5	8
pH	5.8	6.6	7.5	7.8	8.1	8.3

Example 10

1.36 gm of formulation D was added to 250 gm of deionized water in a blender and mixed for 30 seconds at 2800 rpm. This fluid formed a crosslinked gel in about 3-4 minutes. The pH of the sample is monitored as a function of time with the results set forth in Table VIII.

	TABLE VIII
	Time(min)
	1	2	3	4
pH	7	7.4	7.9	8.1

Example 11

1.25 gm of formulation C was added to 250 gm of deionized water in a blender and mixed for 30 seconds at 2800 rpm. The fluid was then placed in a beaker and then the viscosity measured at 5.11/sec using an OFITE Model 900 viscometer. The development of the viscosity was monitored as a function of time. The rapid development of viscosity is an indication of gel formation. The pH at the end of the test is about 9. The viscosity achieved at various time at 75 F. at various intervals was measured with the results set forth in Table IX.

TABLE IX
Viscosity vs. Time
time(min)	Viscosity, cP @5.11/sec	T(F.)
1	6.4	75
1.5	16	75
2	22.3	75
2.5	31.4	75
3	67	75
3.5	106	75
4	136	75
4.5	207	75
5	282	75
5.5	386	75
6	577	75
7	1892	75
8	2287	75
9	2720	75
10	3100	75

Example 12

This example shows that a successful crosslinked gel can be obtained by adding the ingredients separately. 1.2 gm of guar3 and 0.01 gm of fumaric acid are added to 250 gm of deionized water and mixed at 2800 rpm. After 15 sec, 0.05 gm of boric acid and 0.1 gm of magchem 30 were added. The solution is mixed for another 30 sec. The fluid formed a crosslinked gel in about 3.5 to 4 minutes. The pH of the sample was monitored as a function of time with the results set forth in Table X.

	TABLE X
	Time(min)
	1	2	3	4	5	15
pH	5	6.6	7.4	7.9	8	8.7

This indicates that the different components can be added separately and even if the guar has not fully hydrated when the crosslinker is added, a crosslinked gel is formed if the pH of the system can be adjusted higher by using a slow dissolving high pH buffer.

Example 13 (Comparative)

This comparative example shows that if the pH is increased rapidly before hydration, a good crosslinked gel will not be formed. The difference between Example 12 and Example 13 was the use of slow dissolving high pH buffer, Magchem 30 in Example 12 vs. an immediately acting high pH buffer, potassium carbonate solution, in Example 13. 1.2 gm of guar3 and 0.01 gm of fumaric acid are added to 250 gm of deionized water and mixed at 2800 rpm. After 15 sec, 0.05 gm of boric acid and 0.5 ml of 25% by weight potassium carbonate solution were added. The solution is mixed for another 30 sec. The fluid did not form a crosslinked gel. The pH of the sample was monitored as a function of time with the results set forth in Table XI.

	TABLE XI
	Time(min)
	1	2	3	4	5	15
pH	9	9.02	9	9	9	9

This indicates that if the pH is increased very rapidly in the presence of the crosslinker, hydration is prevented and a good crosslinked gel cannot be formed.

While the invention has been described and illustrated in detail herein, various alternative embodiments should become apparent to those skilled in this art without departing from the spirit and scope of the invention.

Claims

1. A self-hydrating, self-crosslinking dry composition useful in preparing a fracturing fluid upon addition of water, the composition comprising (A) guar powder or a guar derivative powder; (B) crosslinker selected from the group consisting of boric acid, borax, borate ore, boron ore, antimony compounds, aluminum compounds, zirconium compounds, and titanium compounds; and (C) slow dissolving alkaline buffer, wherein the crosslinker (B) is non-encapsulated.

2. The composition of claim 1 wherein (B) is borate ore selected from the group consisting of colemanite and ulexite.

3. The composition of claim 1 wherein the guar or guar derivative powder has a D50 particle size of less than 40μ and upon addition of water reaches at least 50% hydration within 60 seconds at about 21° C.

4. The composition of claim 1 wherein the guar or guar derivative achieves about 70% hydration within 60 seconds at about 21° C.

5. The composition of claim 1 further including (D) hydration buffer selected from the group consisting of fumaric acid, sulfamic acid, adipic acid, citric acid, and acetic acid.

6. The composition of claim 1 wherein the slow dissolving alkaline buffer (C) is selected from the group consisting of magnesium oxide, calcium oxide, and strontium oxide.

7. The composition of claim 1 wherein the slow dissolving alkaline buffer (C) is magnesium oxide.

8. The composition of claim 1 comprising, per 100 parts by weight (A) guar, 1 to 20 parts by weight (B) non-encapsulated crosslinker, 1 to 25 parts by weight (C) slow dissolving alkaline buffer, 0 to 20 parts by weight (D) hydration buffer.

9. The composition of claim 1 comprising, per 100 parts by weight (A) guar, 1 to 20 parts by weight (B) non-encapsulated crosslinker, 1 to 25 parts by weight (C) slow dissolving alkaline buffer, 0.1 to 10 parts by weight (D) hydration buffer.

10. A method of preparing a hydrated, crosslinked fracturing fluid comprising combining water or completion brine with a dry composition according to claim 1.

11. A method of preparing a hydrated, crosslinked fracturing fluid comprising combining water or completion brine in any sequence with (A) guar powder or a guar derivative powder; (B) crosslinker selected from the group consisting of boric acid, borax, borate ore, boron ore, antimony compounds, aluminum compounds, zirconium compounds, and titanium compounds; and (C) slow dissolving alkaline buffer, wherein the crosslinker (B) is non-encapsulated.

12. A method of fracturing an oil or gas containing subterranean formation comprising preparing a hydrated, crosslinked fracturing fluid by adding water or completion brine to the composition of claim 1 without use of a hydrating tank, adding propants, and introducing the resultant hydrated, crosslinked fluid into an oil or gas well.