Microstructure, strength and environmental degradation of proppants

The microstructures of four manufactured proppants are described. As-received, all are stronger in diametral compression than quartz sand; and exposure to 3 N NaCl or MgCl₂ brines at 423 K and 69 M Pa for up to 336 h does not change this. Exposure to 12 wt% HCl + 3 wt% HF at the same temperature and pressure reduces the strengths of the manufactured proppants faster than that of sand. The rate of loss of strength depends on the ratio of proppant to acid present during hydrothermal treatment. After a few hours, however, only the strongest and most acid-resistant manufactured proppants retain any significant strength advantage over sand.