Divalent brine fluids having improved rheology and multifunctional properties

Abstract

A method of improving rheological properties of a divalent brine based downhole treatment fluid at an elevated temperature comprises adding to the divalent brine based downhole treatment fluid a rheological modifier, which comprises a carboxylic acid ester, or a phosphate ester blended with an ethoxylated glycol, or a combination comprising at least one of the foregoing in an amount effective to improve the rheological properties of the divalent brine based downhole treatment fluid at a temperature of greater than about 200° F. The divalent brine based downhole treatment fluid comprises calcium bromide, calcium chloride, zinc bromide, zinc chloride, or a combination comprising at least one of the foregoing.

1 . A divalent brine based downhole treatment fluid comprising:
 about 10 to about 18 pounds per gallons of a divalent brine comprising calcium bromide, calcium chloride, zinc bromide, zinc chloride, or a combination comprising at least one of the foregoing;   about 1 to about 12 pounds of a rheological modifier per barrel of the divalent brine based downhole treatment fluid, the rheological modifier comprising a carboxylic acid ester, or a phosphate ester blended with an ethoxylated glycol, or a composition comprising at least one of the foregoing; and   a pH stabilizer comprising a diamine.   
     
     
         2 . The divalent brine based downhole treatment fluid of  claim 1 , wherein the carboxylic acid ester has a formula I or II 
       
         
           
           
               
               
           
         
       
       wherein R 1  and R 2  are each independently a C 6-20  alkyl, C 6-20  alkenyl, or C 6-20  alkynyl group. 
     
     
         3 . The divalent brine based downhole treatment fluid of  claim 1 , wherein the ethoxylated glycol comprises ethoxylated ethylene glycol, ethoxylated propylene glycol, ethoxylated glycerin, ethoxylated polyethylene glycol, ethoxylated polypropylene glycol, or a combination comprising at least one of the foregoing; and the phosphate ester is a hydrocarbyl polyether phosphate ester optionally comprising one or two hydroxyl groups directly attached to phosphorus. 
     
     
         4 . The divalent brine based downhole treatment fluid of  claim 1 , wherein the fluid has a pH of greater than about 7.5. 
     
     
         5 . The divalent brine based downhole treatment fluid of  claim 1 , wherein the divalent brine based downhole treatment fluid comprises about 1 to about 12 pounds of the rheological modifier per barrel of the divalent brine based downhole treatment fluid. 
     
     
         6 . The divalent brine based downhole treatment fluid of  claim 1 , wherein the divalent brine based downhole treatment fluid comprises about 0.5 to about 4 pounds of the rheological modifier per barrel of the divalent brine based downhole treatment fluid. 
     
     
         7 . The divalent brine based downhole treatment fluid of  claim 1 , wherein the divalent brine based downhole treatment fluid comprises about 10 to about 18 pounds per gallons of calcium bromide, calcium chloride, or a combination thereof. 
     
     
         8 . The divalent brine based downhole treatment fluid of  claim 1 , further comprising one or more of the following additional component: a fluid loss control agent; a lubricant; a viscosifier; a pH modifier; or a weighting agent. 
     
     
         9 . The divalent brine based downhole treatment fluid of  claim 1 , wherein the divalent brine based downhole treatment fluid is a drilling or servicing fluid. 
     
     
         10 . The divalent brine based downhole treatment fluid of  claim 1 , wherein the fluid has a yield point of about 20 lb/100 ft 2  to about 40 lb/100 ft 2  and a plastic viscosity of 26 cP to 38 cP, each determined by OFITE 900 viscometer at 120° F., after hot rolled the fluid at 250° F. 
     
     
         11 . The divalent brine based downhole treatment fluid of  claim 1 , having a low shear rate viscosity of greater than 10,000 cP measured by Brookfield viscometer using spindle S62 at 0.5 rpm. 
     
     
         12 . The divalent brine based downhole treatment fluid of  claim 1 , having a lubricity coefficient of less than 0.13 measured by an OFITE Lubricity Meter. 
     
     
         13 . A method of conducting a wellbore operation in a subterranean formation, the method comprising: employing in the wellbore operation a divalent brine based downhole treatment fluid of  claim 1 . 
     
     
         14 . A method of improving rheological properties of a divalent brine based downhole treatment fluid at an elevated temperature, the method comprising:
 adding to the divalent brine based downhole treatment fluid   a rheological modifier comprising a carboxylic acid ester, in an amount effective to improve the rheological properties of the divalent brine based downhole treatment fluid at a temperature of greater than about 200° F., and   a pH stabilizer comprising a diamine,   the divalent brine based downhole treatment fluid comprising calcium bromide, calcium chloride, zinc bromide, zinc chloride, or a combination comprising at least one of the foregoing.   
     
     
         15 . The method of  claim 14 , wherein the carboxylic acid ester has a formula 
       
         
           
           
               
               
           
         
       
       wherein R 1  and R 2  are each independently a C 1-26  alkyl, C 2-26  alkenyl, or C 2-26  alkynyl group. 
     
     
         16 . The method of  claim 15 , wherein R 1  is a C 6-20  alkyl, C 6-20  alkenyl, or C 6-20  alkynyl group; and R 2  is methyl. 
     
     
         17 . The method of  claim 14 , wherein the rheological modifier is added to the divalent brine based downhole treatment fluid in an amount of about 1 to about 12 pounds of the rheological modifier per barrel of the divalent brine based downhole treatment fluid. 
     
     
         18 . The method of  claim 14 , wherein the divalent brine based downhole treatment fluid comprises about 10 to about 18 pounds per gallons of calcium bromide, calcium chloride, or a combination thereof. 
     
     
         19 . The method of  claim 14 , further comprising adding one or more of the following additional component to the divalent brine based downhole treatment fluid: a fluid loss control agent; a lubricant; a viscosifier; a pH modifier; or a weighting agent. 
     
     
         20 . The method of  claim 14 , wherein the rheological properties comprise yield point, low-shear-rate-viscosity, or a combination comprising at least one of the foregoing.