Divalent cation-containing well drilling and service fluid

摘要

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° F.; (c) a fluid loss less than about 10 milliliters as measured at 185° 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° F.