Abstract: Improved high temperature, low residue viscous well treating fluids and methods of using the fluids are provided by the present invention. The improved viscous well treating fluids are basically comprised of water; a hydrated galactomannan gelling agent; a retarded cross-linking composition for buffering the treating fluid and cross-linking the hydrated galactomannan gelling agent comprised of a liquid solvent, an organotitanate chelate and a borate ion producing compound; and a delayed gel breaker.

Abstract: The present invention provides methods and apparatus for determining the gas permeability of very low permeability subterranean formations as well as the gas permeability reducing effects of injecting one or more treatment fluids thereinto. A gas is injected into a core sample of the formation at a selected substantially constant pressure, and the injection is continued for a long period of time to insure steady state flow conditions. The temperature of the gas as it flows through the core sample and the flow rate of the gas exiting the core sample are measured, and the native state gas permeability of the core sample is calculated therefrom. One or more treatment fluids can be injected into the core sample after the native state permeability is determined. Thereafter, the gas permeability can again be determined and compared to the native state permeability.