DIVALENT BRINE FLUIDS HAVING IMPROVED RHEOLOGY AND MULTIFUNCTIONAL PROPERTIES
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.