Enhanced Geothermal Systems (EGS) and some hydrocarbon recovery systems rely on engineered reservoirs, bores, or wells introduced into the earth surface to recover energy producing materials from beneath the earth's surface.  However, recovering energy-producing materials from subterranean bedrock or shale rock beneath the earth's surface is not easily achieved in a cost-effective or efficient manner due to a lack of permeability in native bedrock at depths.  Bedrock must be extensively fractured to provide necessary heat exchange or to provide accessibility for fluid volumes at flow rates that sustain EGS and some hydrocarbon recovery systems. However, to date, EGS systems have yet to attain sustainable flow rates, production rates, and/or yields needed for economic viability. Accordingly, new fracturing fluids, proppants, and processes are needed that enhance fracturing, permeability, and/or recovery of energy producing materials at high temperature and high pressure conditions. The present invention addresses these needs.

Hydraulic fracturing (“fracking”) utilizes millions of gallons of hydraulic fluids (typically water, with certain additives) under high pressure for oil and gas well stimulation.  As an alternative, poly(allylamine) aqueous solution (“PAA”) undergoes a chemically induced reaction with carbon dioxide (CO₂) to form a hydrogel with a large and rapid 100% volume expansion and 15x viscosity increase.  This volume expansion readily and reliably fractures subterranean rock at an effective pressure of 100 psi.  The process is rheoreversible and release of the CO₂ pressure reverses the expansion and viscosity increase, thus allowing for the fluid to be removed from the well and re-used.

The polymer is used at a 1% concentration.  Proppants are used as for conventional fracking. Depending upon the polymer used, the rheological properties can be tailored to the specific application to aid in oil migration to the surface. For geothermal applications, the fracking and rheoreversiblity works at temperatures up to at 400 C.