Synthesis and microstructural evolution in iron oxide kaolinite based proppant as a function of reducing atmosphere, sintering conditions, and composition

An ideal proppant for hydraulic fracturing should be neutrally buoyant, implying a very low bulk specific gravity, while maintaining crush resistance and low acid solubility. To this end, an iron oxide and kaolinite based proppant has been developed. In this work, synthesis conditions are explored by varying partial pressures of oxygen from 1.772 × 10–13 atm to 1.821 × 10–11 atm. The Fe2O3 reduces to FeO and reacts with kaolinite decomposed to mullite to form Fe2SiO4, FeSiO3, and FeAl2O4. As a result, the proppant develops large pores (~100 µm), giving it a low bulk density (1.43 g/cm3), and high porosity (45.2 vol%) at PO2 of 1.821 × 10–11 atm. The proppant sintered at PO2 of 1.772 × 10–13 atm is characterized by smaller pores (26 µm), higher density (1.72 g/cm3) and lower porosity (37.5 vol%). Crush resistance testing at 9000 psi yields 6.8 wt% fine particles increasing to 17.7 wt% in porous samples. Acid solubility varies from 5.5 wt% loss increasing to 12.9 wt% in porous samples. A wide variety of microstructures with associated mechanical and chemical features are possible when composition, partial pressure of oxygen and temperature are varied during sintering.