A method of propping fractures in a subterranean formation whereby a high viscosity fluid is introduced into the formation to open and extend the fractures, the high viscosity fluid containing slugs of a hardenable liquid which are carried into and held in spaced relationship in the fractures and permitted to harden therein whereby the fractures are propped in the open position.

A method for hydraulically fracturing a single subterranean formation in which a fracture is first induced in the formation and then subjected to multiple hydraulic fracturing cycles to generate vertical linear fractures or to linearly extend the fracture outward from the point of introduction of the fracing fluid into a well penetrating the formation. By utilizing fracing fluid containing a high ratio of fine proppant and injected at a low rate, the linear fracturing solely within the formation can be substantially increased with very little or no radial vertical fracturing occurring outside the formation.

A method for enhanced hydraulic fracturing which comprises injecting a proppant laden fracturing fluid into a formation or reservoir at a rate and pressure sufficient to fracture said formation. Next, a thin spacer fluid is injected into the created fracture. Afterwards, a proppant laden fracturing fluid is injected into the formation at a rate and pressure sufficient to hold the created fracture open which allows proppant to be more evenly distributed throughout the created fracture as proppant falls through the spacer fluid thereby avoiding proppant convection in the created fracture while obtaining substantially improved propping of the fracture.

In the preferred embodiment of the present invention, completion operations are performed which include a perforation operation followed by a fracturing operation. During the perforation operation perforations (or other means for creating flow paths) are shot at a low perforation density, in order to create a flowpath between the wellbore and the hydrocarbon bearing formation as well as an unknown number of relatively wide fractures and relatively few, but unknown number of fracture initiation sites in the hydrocarbon bearing formation. During the fracturing operations, relatively small, high-concentration proppant slugs with clean spacer stages are pumped early in the treatment, in order to screenout the narrower fractures, but these slugs are not sufficient to screenout the wider fractures. Next, conventional fracturing operations are employed to create and/or enlarge and widen the remaining wider fractures, without the risk of loss of relatively-expensive carrier fluids and proppant material (such as sand) to the now-screened-out smaller fractures. Experimentation has revealed that this technique can be employed to (1) likely create longer and wider fractures, and (2) increase the overall sand-to-fluid ratios.

Water injection wells are fractured by a proppant-laden fracturing fluid to create a propped fracture and wherein the proppant-laden fluid is followed by injection of a substantially proppant-free fluid so that the near wellbore portion of the fracture is free of proppant to minimize pressure drop during water injection and to produce higher injection rates for a given injection pressure. The fracture treatment may include the use of viscous fracturing and displacement fluids which are degraded by the injection of acid-bearing fluids at the end of the fracture treatment cycle. Stimulation or displacement liquid (water) injection may commence immediately after the fracture treatment and may be alternated with miscible gas injection.