US Patent 9644137 Method of cryogenic acid fracking

A method of fracking carbonate-rich reservoirs, comprising injecting a cryogenic or chilled fluid followed by an acid into the reservoir, allowing the acid to etch the reservoir, and thereby increasing production of a fluid, such as water, oil or gas, from the reservoir. Further, injecting a preflush into the reservoir and later injecting a postflush into the reservoir to displace the acid from the tubulars into the reservoir.