Divalent brine fluids having improved rheology and multifunctional properties

1. A divalent brine based downhole treatment fluid comprising:

about 10 to about 18 pounds per gallon of a divalent brine comprising calcium bromide, calcium chloride, zinc bromide, zinc chloride, or a combination comprising at least one of the foregoing;

a rheological modifier present 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 rheological modifier comprising a phosphate ester blended with an ethoxylated glycol, and the divalent brine based downhole treatment fluid comprising about 0.5 to about 4 pounds of the rheological modifier per barrel of the divalent brine based downhole treatment fluid; and

a pH stabilizer comprising a diamine,

wherein the phosphate ester is a hydrocarbyl polyether phosphate ester optionally comprising one or two hydroxyl groups directly attached to phosphorus,

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 divalent brine based downhole treatment fluid has a pH of greater than about 7.5.

2. 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 gallon of calcium bromide, calcium chloride, or a combination thereof.

3. 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.

4. The divalent brine based downhole treatment fluid of claim 1 , wherein the divalent brine based downhole treatment fluid is a drilling fluid, a completion fluid, or a servicing fluid.

5. The divalent brine based downhole treatment fluid of claim 1 , wherein the rheological properties comprise yield point, low-shear-rate-viscosity, or a combination comprising at least one of the foregoing.

6. The divalent brine based downhole treatment fluid of claim 1 , wherein the diamine in the pH stabilizer is ethylene diamine, and the pH stabilizer further comprises about 1 to about 5 wt. % of a polyimidazoline, based on the total weight of the pH stabilizer.

7. 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.

8. 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.

9. 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.

10. 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 .

11. The method of claim 10 , wherein the wellbore operation is a drilling operation, and the method comprises circulating the divalent brine based downhole treatment fluid in the subterranean formation.

12. The divalent brine based downhole treatment fluid of claim 1 , wherein the diamine in the pH stabilizer is ethylene diamine.