Methods of using a higher-quality water with an unhydrated hydratable additive allowing the use of a lower-quality water as some of the water in the forming and delivering of a treatment fluid into a wellbore

Abstract

The inventions are for methods of forming and delivering a treatment fluid into a wellbore. In one aspect, methods are provided of using higher-quality water for one portion of the water for a treatment fluid and lower-quality water for another portion of the water for a treatment fluid, and merging the two portions to form the treatment fluid after pumping the fluid portions toward the wellbore. This allows the use of lower-quality water for some of the water required for making up the treatment fluid.

1 . A method of forming and delivering a treatment fluid into a wellbore, the method comprising the steps of:
 (a) forming a premix fluid comprising:
 (i) an unhydrated hydratable additive; and 
 (ii) a first aqueous solution; 
   (b) subsequently forming a treatment fluid comprising:
 (i) the premix fluid; and 
 (ii) a second aqueous solution; and 
   (c) simultaneously with or subsequently to the step of forming the treatment fluid, delivering the treatment fluid into the wellbore;   wherein:
 (i) the first aqueous solution has a concentration of at least one ion that is substantially lower than the concentration of the at least one ion in the second aqueous solution; and 
 (ii) the treatment fluid has a merged viscosity of less than 100 cP at 40 l/s and at 25° C. (77° F.). 
   
   
   
       2 . The method according to  claim 1 , wherein the at least one ion is selected from the group consisting of calcium, magnesium, sulfate, iron, and borate. 
   
   
       3 . The method according to  claim 1 , wherein the step of forming the premix fluid is under conditions sufficient to form a premix fluid comprised of at least 50% by weight of the first aqueous solution. 
   
   
       4 . The method according to  claim 1 , wherein the step of forming a treatment fluid is under sufficient conditions to form the treatment fluid to comprise at least 10% by weight of the first aqueous solution and at least 10% by weight of the second aqueous solution. 
   
   
       5 . The method according to  claim 1 , wherein the step of forming the premix fluid further comprises mixing under at least sufficient conditions of concentration of the unhydrated hydratable polymer in the first aqueous solution, shear, time, temperature, and pH for the hydratable polymer to hydrate greater than 50% when measured by viscosity prior to the step of forming a treatment fluid, whereby the mixing conditions help avoid the formation of gel balls. 
   
   
       6 . The method according to  claim 1 , wherein the step of delivering the treatment fluid is immediately after the step of forming a treatment fluid. 
   
   
       7 . The method according to  claim 6 , wherein the steps of forming the premix fluid, forming the treatment fluid, and delivery the treatment fluid are performed continuously. 
   
   
       8 . The method according to  claim 1 , further comprising a step of treating a base aqueous solution to obtain the first aqueous solution having a substantially reduced concentration of at least one ion relative to the concentration of the at least one ion in the base aqueous solution. 
   
   
       9 . The method according to  claim 8 , wherein the base aqueous solution is selected to be the same as the second aqueous solution. 
   
   
       10 . The method according to  claim 1 , wherein the step of delivering comprises:
 (a) pumping the premix fluid with a first positive displacement pump;   (b) pumping a second fluid comprising the second aqueous solution with a second positive displacement pump;   (c) merging at least the premix and second fluids to form a treatment fluid; and   (d) directing the treatment fluid into a wellbore;    wherein:
 (i) the treatment fluid comprises a merged concentration of a particulate; 
 (ii) the premix fluid comprises a first concentration of the particulate that is substantially higher than the merged concentration of the particulate; 
 (iii) the second fluid comprises a second concentration of the particulate that is substantially lower than the merged concentration of the particulate; and 
 (iv) the premix fluid is pumped at a substantially lower average bulk fluid velocity than the average bulk fluid velocity at which the second fluid is pumped. 
   
   
   
       11 . The method according to  claim 1 , wherein the step of delivering comprises:
 (a) pumping the premix fluid with a first positive-displacement pump;   (b) pumping a second fluid comprising the second aqueous solution with a second positive-displacement pump;   (c) merging at least the premix and second fluids to form a treatment fluid; and   (d) directing the treatment fluid into a wellbore;    wherein:
 (i) the treatment fluid comprises a merged concentration of a particulate and a merged concentration of the hydratable additive; 
 (ii) the premix fluid comprises a first concentration of the particulate that is substantially higher than the merged concentration of the particulate and a first concentration of the additive that is substantially higher than the merged concentration of the additive; 
 (iii) the second fluid comprises a second concentration of the particulate that is substantially lower than the merged concentration of the particulate and a second concentration of the additive that is substantially lower than the merged concentration of the additive. 
   
   
   
       12 . A method of forming and delivering a treatment fluid into a wellbore, the method comprising the steps of:
 (a) forming a premix fluid comprising:
 (i) an unhydrated hydratable additive; and 
 (ii) a first aqueous solution; 
   (b) subsequently forming a treatment fluid comprising:
 (i) the premix fluid; and 
 (ii) a second aqueous solution; and 
   (c) simultaneously with or subsequently to the step of forming the treatment fluid, delivering the treatment fluid into the wellbore;   wherein:
 (i) the first aqueous solution has combined dissolved calcium and magnesium ions of less than 10,000 ppm; and 
 (ii) the second aqueous solution has combined dissolved calcium and magnesium ions of greater than 15,000 ppm; and 
 (iii) the treatment fluid has a merged viscosity of less than 100 cP at 40 l/s and at 25° C. (77° F.). 
   
   
   
       13 . The method according to  claim 12 , wherein the first aqueous solution has combined dissolved calcium and magnesium ions of less than 5,000 ppm. 
   
   
       14 . The method according to  claim 12 , wherein the first aqueous solution has combined dissolved calcium and magnesium ions of less than 1,000 ppm. 
   
   
       15 . A method of forming and delivering a treatment fluid into a wellbore, the method comprising the steps of:
 (a) forming a premix fluid comprising:
 (i) an unhydrated hydratable polymer; and 
 (ii) a first aqueous solution; 
   (b) subsequently forming a treatment fluid comprising:
 (i) the premix fluid; and 
 (ii) a second aqueous solution; and 
   (c) simultaneously with or subsequently to the step of forming the treatment fluid, delivering the treatment fluid into the wellbore;   wherein:
 (i) the first aqueous solution has total dissolved solids of less than 30,000 ppm; and 
 (ii) the second aqueous solution has total dissolved solids of greater than 40,000 ppm; and 
 (iii) the treatment fluid has a merged viscosity of less than 100 cP at 40 l/s and at 25° C. (77° F.). 
   
   
   
       16 . The method according to  claim 15 , wherein the first aqueous solution has total dissolved solids of less than 15,000 ppm. 
   
   
       17 . The method according to  claim 15 , wherein the first aqueous solution has total dissolved solids of less than 1,000 ppm.