US Patent 9617841 Hydraulic fracturing ball sealers

A hydraulic fracturing ball sealer used in fracturing of shale formations. A preferred embodiment is constructed of a generally spherical core and a pair of hemispherical shells positioned about the core. The shells are secured to each other along an equatorial seam. The multilayer frac-ball provides a strong but machinable structure with a pliable outer surface that is corrosion resistant, has a specific gravity that allows it to float in the fracturing fluid, and is relatively easy and inexpensive to manufacture. The frac-ball of the present invention is a two piece metal and polymer design. A two-part embodiment comprises a polymer core with a metal case or shell. A layer of epoxy resin may be used to secure the shell to the core. Alternate embodiments include multiple layers of different materials, generally arranged concentrically within the spherical shape. The surface of the frac-ball may be smooth, scored, or serrated.