Delayed Viscosity Well Treatment Methods and Fluids

Abstract

A well treatment method includes forming a well treatment fluid by combining ingredients including a polymer, a crosslinker, an acidifying substance, and a base fluid. Crosslinking increases viscosity of the fluid during a development time. A pH decrease is controlled during the development time using the acidifying substance. The method also includes delaying the development time of the viscosity increase by controlling the pH decrease. A well treatment method includes forming a well treatment fluid by combining ingredients including a hydratable polymer, a crosslinker, an acidifying substance, and a base fluid. The method includes delaying development time of a viscosity increase by controlling a pH decrease without adding further acidifying substance after combining the polymer, crosslinker, acidifying substance, and base fluid. A well treatment fluid formulated with ingredients include a base fluid, a polymer, a crosslinker, and an acidifying substance. The acidifying substance is configured to delay development time.

What is claimed is: 
     
         1 . A well treatment fluid formulated with ingredients comprising:
 a base fluid, a polymer, a crosslinker, and an acidifying substance;   the polymer and crosslinker being configured, in combination, to crosslink the polymer in the base fluid and thereby to increase viscosity of the well treatment fluid during a development time of a viscosity increase after combining the polymer, crosslinker, acidifying substance, and base fluid; and   the acidifying substance being configured to decrease pH, to control a pH decrease during the development time of the viscosity increase in the well treatment fluid, and to delay the development time of the viscosity increase, the pH decrease facilitating the crosslinking that uses the crosslinker.   
     
     
         2 . The fluid of  claim 1  wherein the polymer comprises hydratable, derivatized guar or cellulose, CMG, HPG, CMHPG, CMC, CMHEC, or synthetic polymer. 
     
     
         3 . The fluid of  claim 1  wherein the polymer comprises CMG, HPG, CMHPG, CMC, or CMHEC. 
     
     
         4 . The fluid of  claim 1  wherein the acidifying substance comprises a water-soluble solid acid, a water-soluble liquid acid, a latent acid, or an acid-generating compound. 
     
     
         5 . The fluid of  claim 1  wherein the acidifying substance comprises a water-soluble solid acid slurried in a hydrocarbon liquid. 
     
     
         6 . The fluid of  claim 1  wherein the acidifying substance exhibits increased solubility in water at increasing temperatures above 75° F. 
     
     
         7 . The fluid of  claim 1  wherein the acidifying substance comprises solid fumaric acid. 
     
     
         8 . The fluid of  claim 1  wherein the development time is at least one minute. 
     
     
         9 . The fluid of  claim 1  further comprising one or more ingredients selected from the group consisting of proppant and clay control agents. 
     
     
         10 . The fluid of  claim 1  wherein the crosslinking occurs at a pH no more than 6.8. 
     
     
         11 . The fluid of  claim 1  wherein the viscosity is greater than 100 cP after the development time. 
     
     
         12 . A well treatment fluid formulated with ingredients comprising:
 an aqueous-based fluid, a polymer containing CMG, HPG, CMHPG, CMC, or CMHEC, a crosslinker, and an acidifying substance containing a water-soluble solid acid, a water-soluble liquid acid, a latent acid, or an acid-generating compound and exhibiting increased solubility in water at increasing temperatures above 75° F.;   the polymer and crosslinker being configured, in combination, to crosslink the polymer in the base fluid and thereby to increase viscosity of the well treatment fluid during a development time of a viscosity increase after combining the polymer, crosslinker, acidifying substance, and base fluid; and   the acidifying substance being configured to decrease pH, to control a pH decrease during the development time of the viscosity increase in the well treatment fluid, and to delay the development time of the viscosity increase, the pH decrease facilitating the crosslinking that uses the crosslinker.   
     
     
         13 . The fluid of  claim 12  wherein the acidifying substance comprises a water-soluble solid acid slurried in a hydrocarbon liquid. 
     
     
         14 . The fluid of  claim 12  wherein the acidifying substance comprises solid fumaric acid. 
     
     
         15 . The fluid of  claim 12  wherein the development time is at least one minute. 
     
     
         16 . The fluid of  claim 12  further comprising one or more ingredients selected from the group consisting of proppant and clay control agents. 
     
     
         17 . The fluid of  claim 12  wherein the crosslinking occurs at a pH no more than 6.8. 
     
     
         18 . The fluid of  claim 12  wherein the viscosity is greater than 100 cP after the development time. 
     
     
         19 . A well treatment fluid formulated with ingredients comprising:
 an aqueous-based fluid;   a polymer containing CMG, HPG, CMHPG, CMC, or CMHEC;   a crosslinker; and   a water-soluble solid acid slurried in a hydrocarbon liquid, the solid acid exhibiting increased solubility in water at increasing temperatures above 75° F.   
     
     
         20 . The fluid of  claim 19  wherein the water-soluble solid acid comprises solid fumaric acid.