Patent ID: 6300286
Filing Date: 2001-10-09
Classification: C09K,Y10S

Abstract:
A clay-free well and servicing fluid comprising an aqueous brine containing at least 0.6 equivalents per liter of a water soluble divalent cation salt, a particulate bridging agent which is insoluble in the aqueous liquid, and a starch derivative wherein the concentration of the starch derivative is sufficient to provide the fluid with the following characteristics: (a) a low shear rate viscosity less than about 10,000 centipoise; (b) a high shear rate viscosity at 511 sec.sup.-1 in the range from about 15 to about 70 centipoise measured at 120.degree. F.; (c) a fluid loss less than about 10 milliliters as measured at 185.degree. 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.degree. F., and wherein the starch derivative comprises a pre-gelatinized crosslinked amylopectin starch which has been crosslinked to the extent that the viscosity of a basic aqueous amylopectin starch suspension undergoing crosslinking is within about 25% to less than about 50% of the maximum viscosity which can be obtained.