Divalent brine fluids having improved rheology and multifunctional properties

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.