EXAMPLE 10
A protected particle was formed of a base particle having an average diameter of 40 μm. The base particle is a hollow sphere having a shell thickness of 1 μm. The interior pressure in the hollow cavity of the base particle is 1000 psi. The density of the base particle is 0.39 g/cc. The outer surface of the base particle was coated with a PVA by suspension deposition. The coating thickness was 68 μm. The protected particle had a crush strength of about 8000 psi. The protected particles were subjected to well conditions of 10,000 ppm brine solution at a pH of 8, a temperature of 80° C., and under 6,000 psi hydrostatic pressure. After about 36 hours and over the period of 72 hours thereafter, the base particles were fractured or crushed. The acoustic sound or emission created by the fractured or crushed base particles had a traceable harmonic resonant frequency peak at 600 Hz. As is evident from Examples 9 and 10, the protected particle can be tailored by using certain pressures in the hollow cavity of the base particle to create a certain frequency or range of frequencies when the base particle fractures or crushes.
