Abstract: An environmentally acceptable water-in-oil microemulsion composition includes at least one emulsifying surfactant, at least one biodegradable hydrocarbon solvent, at least one co-solvent, at least one hydrocarbon co-surfactant, and water. The microemulsion composition may be used in a method for rendering fluids from oil external to water external. The microemulsion composition may be combined with water or a water based fluid to produce a spacer fluid utilized in removing oil and oil-residues from a surface, particularly that of wellbores in the drilling of oil and gas wells.

Abstract: A method is provided for controlling the delay time of aqueous borate-crosslinked polysaccharide-based fluids for hydraulic fracturing and related applications which allows on-the-fly control of the delay time without comprising overall fluid integrity. Without having to modify the total boron content nor pH of the fracturing fluid, the delay time is controlled by adding a polyol to the fracturing fluid at a first rate, determining the resulting delay time and then adjusting the rate of the polyol addition to the fracturing fluid until the desired delay time is achieved.