Divalent cation-containing well drilling and servicing fluids

The invention provides clay-free, preferably biopolymer free, well drilling and servicing fluids comprising an aqueous divalent cation-containing water soluble salt, a bridging agent, and a pre-gelatinized crosslinked amylopectin starch suspending agent and fluid loss control additive. The concentration of the starch derivative is sufficient to provide the fluid with the following charactersitics: (a) a low shear rate viscosity less than about 10,000 centipoise; (b) a high shear rate viscosity at 511 sec<-1> in the range from about 15 to about 70 centipoise measured at 120 DEG F; (c) a fluid loss less than about 10 milliliters as measured at 185 DEG F and 250 psi differential pressure across a 5 micron disk for 30 minutes; and (d) anti-settling characteristics as exhibited upon static aging the fluid for 16 hours at 185 DEG F. The low shear rate viscosity of the fluids can be increased without increasing the high shear rate viscosity above about 70 centipoise by incorporating magnesium oxide and/or dipotassium hydrogen phosphate in the fluids. The invention also provides a method of making the clay-free well drilling and servicing fluid and a process of drilling, completing, and working over a well with the clay-free fluid.