Self-suspending proppants for hydraulic fracturing

An aqueous fracturing fluid which is made by combining an aqueous carrier liquid and a mass of discrete proppant particles, the discrete proppant particles comprising a modified proppant comprising a proppant particle substrate and a hydrogel coating on the proppant particle substrate,

• wherein the hydrogel coating comprises an anionic polyacrylamide which has been crosslinked by means of a subsequently applied cross-linker selected from the group consisting of an epoxide, an anhydride, an aldehyde, a diisocyanate and a carbodiamide in an amount sufficient to prevent premature hydration of the modified proppant due to humidity prior to the combining of the modified proppant with the aqueous carrier liquid forming the aqueous fracturing fluid,
• wherein 1 gram of the modified proppant when mixed with water in a 20 ml glass vial and allowed to sit undisturbed for 30 minutes exhibits an expanded settled bed height which is about 3 (2.7/0.8) to about 28 (22.6/0.8) times greater than the settled bed height of an otherwise identical proppant not modified with a hydrogel coating, and
• wherein the modified proppant substantially retains its expanded settled bed height after having been subjected to shear at a shear rate of about 550 s−1 for 20 minutes.