Abstract: A viscosity-increased liquid carbon dioxide fracturing fluid is provided for the treatment of subterranean gas-bearing formations. The composition comprises liquid carbon dioxide which has been thickened by the addition of a small amount of a copolymer which is the reaction product of liquid carbon dioxide and an alkene oxide, preferably propylene oxide. The use of the copolymer thickener provides a CO.sub.2 fracturing fluid which may be pumped at a high rate, will not readily boil or foam, will carry a propping agent and will completely degrade within the formation.

Abstract: This invention is concerned with an apparatus for concentrating a proppant fluid slurry. The concentration is carried out in a casing containing an axial elongated screen. Stationary angled vanes direct the slurry in a helical path in the space between the casing and the elongated tubular screen to avoid the problems of rotating members. The concentrating zone thus provided communicates with a mixing zone where baffles provide restricted flow between the edges of the baffles and the interior of the casing to give a mixing action, disperse slugs of slurry, and to avoid back flow of gas. The baffles are advantageously of resilient material. The mixing zone then leads to a foaming zone, followed by the outlet. It is advantageous to have inlet, concentrating zone, mixing zone, foaming zone and outlet for the foamed slurry in axial alignment and without interruptions so as to give a straight through flow.

Abstract: There is described a new and improved method of fracturing an underground stratigraphic formation penetrated by a well bore including the steps of pumping a stream of liquified gas into the formation to cause the fracturing thereof and then introducing proppants directly into the stream of liquified gas for injection of the proppants into the fractures. Prior to introducing the proppants into the liquid gas stream, they are cooled and pressurized to the storage temperature and pressure of the liquified gas.

Abstract: A bypass attachment is provided to prevent damage to the valves of a well tree when fluid at high pressure is passed into a well, such as during a fracturing process. The bypass attachment is formed of a piston rod removably mounted to the well tree and offset from it, a piston mounted on the piston rod, a cylinder movable on the piston, the cylinder bearing a piece of high-pressure tubing aligned with the passage through the well-head tree, a high-pressure valve to close off the high-pressure tubing and sealing means to seal the space between the exterior of the high-pressure tubing and the interior of the vertical passage through the well-head tree.