Crush resistance has become a key, perhaps even the singular, parameter used in selection of proppant for hydraulic fracture stimulation operations. The API Recommended Practice 19C (RP19C)—which is identical to the ISO13503-2 standard1— lays out procedures intended to produce repeatable results.
However, repeated measurements in the same lab are inherently noisy and lab-to-lab results often produce crush strength differences of as much as 2k psi. The RP19C is intended to produce reliable and repeatable proppant crush results. However, results from this study show that when compared to other possible methods, the RP19C procedure both increases the noise in the measurement and lowers the crush rating. We describe a series of experiments which provide statistically reliable insight on the effect that loading and handling of the crush cell has on the crush results. The data allow a comparison of five loading methods: the standard RP19C method; the Pluviator; a jarred-cell approach to test the RP19C admonition to avoid "agitating" the cell; a vibratory settling method and a new mechanical loader, designed by the authors. Because two of the loading methods produce statistically significant improvements in crush resistance (specifically the vibratory method and the new mechanical loading device) and because the primary effect appears to be tied to maximizing the packing density, we conclude that the in-situ crush resistance of these proppants may be higher than estimated by the standard test.