CARBOXYLATED CELLULOSE POLYMERS FOR USE IN HYDRAULIC FRACTURING OPERATIONS
A low residue fracturing fluid comprises water, an acidified carboxylated gelling agent in an amount in the range of from about 0.06% to about 0.48% by weight. The fracturing fluid can further include a stabilizer agent, a cross-linker, and a buffer.
1 . A method of preparing a low residue fracturing fluid, the method comprising in the following order:
(a) hydrating a carboxylated gelling agent in an aqueous dispersion to form a hydrated carboxylated gelling agent;
(b) adjusting the pH of the aqueous dispersion including the hydrated carboxylated gelling agent to less than 6 to form an acidified carboxylated gelling agent; and
(c) mixing an oxygen scavenger and a cross-linking agent in the aqueous dispersion having a pH less than 6 and containing the acidified carboxylated gelling agent.
2 . The method of claim 1 , wherein an amount of the hydrated gelling agent is in the range from 0.06 wt % to 0.48 wt % based on a total weight of the fracturing fluid.
3 . The method of claim 2 , wherein the amount of the hydrated gelling agent is in the range from 0.06 wt % to 0.25 wt % based on a total weight of the fracturing fluid.
4 . The method of claim 1 , wherein the low residue fracturing fluid has a peak viscosity at 175° F. of at least 2000 cP at 0.25 wt % amount of acidified carboxylated gelling agent.
5 . The method of claim 1 , wherein mixing of the oxygen scavenger and the cross-linking agent with the acidified carboxylated gelling agent is conducted at least 15 minutes after adjusting the pH to less than 6.
6 . The method of claim 1 , wherein the pH of the aqueous dispersion including the hydrated carboxylated gelling agent is adjusted to a pH of at least 3 and less than 5.5.
7 . The method of claim 1 , wherein the acidified carboxylated gelling agent includes an acidity degree from 30% to 99%.
8 . The method of claim 1 , wherein a viscosity 20 minutes after adding the oxygen scavenger and cross-linking agent increases by a factor f i (T20) of at least 1.3 in comparison to a viscosity obtained by employing a non-acidified hydrated carboxylated gelling agent.
9 . The method of claim 1 , wherein the carboxylated gelling agent includes a carboxylated cellulose, a carboxylated galactomannan, a carboxylated glucomannan, or any combination thereof.
10 . The method of claim 9 , wherein the carboxylated gelling agent includes carboxymethyl cellulose.
11 . The method of claim 1 , further comprising adding at least one non-carboxylated gelling agent.
12 . The method of claim 11 , wherein the non-carboxylated gelling agent includes a galactomannan, a glucomannan, a cellulose, or any combination thereof.
13 . The method of claim 1 , wherein the cross-linking agent includes metal salt, the metal salt including boron, aluminum, zirconium, iron, antimony, titanium, or any combination thereof.
14 . The method of claim 13 , wherein the cross-linking agent is present in an amount of at least 0.1 gpt.
15 . The method of claim 1 , wherein the fracturing fluid further includes a chelating agent, the chelating agent including a diol, a diamine, a dicarboxylic acid, a carboxylic acid, an alkanol amine, a hydroxycarboxylic acid, an aminocarboxylic acid, or any combination thereof.
16 . The method of claim 1 , wherein the oxygen scavenger includes a thiosulfate, a sulfite, a bisulfite, or any combination thereof.
17 . The method of claim 16 , wherein the oxygen scavenger is sodium thiosulfate.
18 . The method of claim 16 , wherein an amount of the oxygen scavenger is at least 1 wt % and not greater than 10 wt % based on a total weight of the fracturing fluid.
19 . A method of treating a subterranean zone penetrated by a well bore comprising:
(a) preparing a low residue fracturing fluid comprising water, an acidified carboxylated gelling agent, a cross-linking agent, an oxygen scavenger, and a delayed gel breaker;
(b) pumping the low residue fracturing fluid into the subterranean zone by way of said well bore at a rate and a pressure sufficient to treat the subterranean zone during which the acidified carboxylated gelling agent is cross-linked by the cross-linking agent in the low residue fracturing fluid, wherein the fracturing fluid has a peak viscosity at 175° F. of at least 2000 cP at 0.25 wt % amount of acidified carboxylated gelling agent; and
(c) allowing the fracturing fluid to break into a thin fluid.
20 . The method of claim 19 , wherein the acidified carboxylated gelling agent is an acidified carboxylated cellulose in an amount from 0.06 wt % to 0.48 wt % based on a total weight of the fracturing fluid.