Abstract: The invention provides alkaline water base well drilling and servicing fluids which deposit an easily degradable and removable filter cake on the sides of a borehole during well drilling and servicing operations. The fluids contain one or more polysaccharide polymers, sized bridging particles, and a peroxide selected from the group consisting of alkaline earth metal peroxides, zinc peroxide, and mixtures thereof. The fluids deposit a filter cake containing the peroxide.

Abstract: The invention provides: (1) a process to enhance the removal of solids such as clays, clay-like solids, and shale solids-drill solids-from the surface of a borehole, the solids being deposited from well drilling, completion, or workover fluids during well servicing operations; and (2) a process to enhance the removal of such solids from screens or other sand control devices present in a borehole. The process comprises contacting the solids with an acidic soak solution containing a polyglycol or mono ether derivative thereof and thereafter contacting the surface of the borehole with a wash solution to remove the solids from the borehole.

Abstract: Disclosed are low solids, high density fluids useful as drilling, workover, and completion fluids and the like in oil and gas well operations. The fluids comprise a brine having dissolved therein a zinc salt such as zinc bromide, and optionally one or more additional water soluble salts, a viscosifier which is a high surface area silica, a biopolymer viscosifier, a fluid loss control additive which is preferably a starch derivative, zinc carbonate, and, optionally, an alkaline buffer, a polar additive, and a bridging agent.It has been found that zinc carbonate will increase the low shear rate viscosity of fluids containing a zinc salt dissolved therein. Additionally, the combination of zinc carbonate and zinc oxide as the alkaline buffer provides fluids having increased thermal stability as indicated by the low shear rate viscosity of the fluids.

Abstract: The invention provides brine based well drilling and servicing fluids which exhibit relatively thermally stable rheological and filtration characteristics. The fluids comprise a brine, an amorphous silica viscosifier, a biopolymer viscosifier, a fluid loss control additive, and a bridging agent. By utilizing both a silica viscosifier and a biopolymer viscosifier to provide the desired rheological characteristics, the fluids have enhanced thermal stability thus maintaining their suspension and hole cleaning properties over an extended temperature range.

Abstract: The invention provides brine based well drilling and servicing fluids containing a fluid loss control additive selected from the group consisting of (1) a crosslinked ether derivative of a partially depolymerized starch, (2) a partially depolymerized crosslinked ether derivative of starch, or (3) mixtures thereof. The fluid loss control additive provides decreased fluid losses at much lower viscosities than the corresponding starch derivatives which have not been partially depolymerized. This enables their use in fluids at concentrations sufficient to provide excellent filtration control, the fluids having a viscosity sufficient for circulation of the fluids in the borehole. The invention also provides a method of reducing the fluid loss of well drilling and servicing fluids utilizing the fluid loss control additives (1) and/or (2).

Abstract: The invention provides methods for (1) reducing the fluid loss of and (2) reducing the concentration of polymer required to provide a desired degree of fluid loss control to, a well drilling and servicing fluid which contains at least one polymeric viscosifier, at least one polymeric fluid loss control additive, and a water soluble bridging agent suspended in an a liquid in which the bridging agent is not soluble, the methods comprising adding to the fluids a particulate, water soluble, ultra fine filtrate reducing agent having a particle size distribution such that at least 90% of the particles thereof are less than 10 micrometers and the average particle size is from about 3 to about 5 micrometers, the ultra fine filtrate reducing agent being insoluble in the liquid.

Abstract: Disclosed are low solids, high density fluids useful as drilling, workover, and completion fluids and the like in oil and gas well operations. The fluids comprise one or more brines having a density greater than about 1500 kg/m.sup.3, a viscosifier which is a high surface area silica, a fluid loss control additive which is preferably a starch derivative, one or more water soluble or acid soluble bridging agents, and, optionally, an alkaline buffer and a polar additive.Also disclosed is an additive for the preparation of low solids, high density fluids which comprises a fumed silica and a bridging agent in a weight ratio of bridging agent to fumed silica from about 2 to about 20, and optionally, an alkaline buffer in a weight ratio of alkaline buffer to fumed silica from about 0.03 to about 2.5.

Abstract: The invention provides alkaline water base well drilling and servicing fluids which deposit an easily degradable and removable filter cake on the sides of a borehole during well drilling and servicing operations. The fluids contain one or more polysaccharide polymers, sized bridging particles, and a peroxide selected from the group consisting of alkaline earth metal peroxides, zinc peroxide, and mixtures thereof. The fluids deposit a filter cake containing the peroxide. The invention also provides processes for enhancing the removal of the filter cake which comprises depositing a peroxide-containing filter cake on the sides of the borehole, or on the filter cake already present on the sides of the borehole, and thereafter contacting the peroxide-containing filter cake with an acidic solution to activate the peroxide which thereafter degrades the polysaccharide polymers in the filter cake.

Abstract: Disclosed are well working and treating fluids comprising a saturated aqueous saline solution, a particulate water soluble salt which is insoluble in the saturated saline solution, xanthomonas gum, and an epichlorohydrin crosslinked hydroxypropyl starch derivative wherein the xanthomonas gum and the epichlorohydrin crosslinked hydroxypropyl starch derivative interact to synergistically enhance the suspension characteristics of the fluid and to decrease the fluid loss of the fluid.Also disclosed is an additive composition for enhancing the suspension characteristics and reducing the fluid loss of saturated brine based well treating fluids comprising specified proportions of xanthomonas gum and epichlorohydrin crosslinked hydroxypropyl starch.