Magnetization characteristics of tracer particle for measurement of subsurface fracture.

Recently it is expected that the technology using magnetic tracer will enable to measure subsurface fractures. The magnetic tracer to be used in the above case is a suspension of magnetic particles and it must be thermally stable and possess high initial magnetic permeability.We measured the initial magnetic permeability of various magnetic particle assemblies such as ferrite and metal materials. Relationship between initial magnetic permeability of particle assembly and of bulk material can be shown experimentally. Function of initial magnetic permeability against volume fraction was simulated using Ollendorf's equation, however its equation was not enough to explain the experimental results. This fact suggests that the effect of static magnetic interaction between particles could not be evaluated sufficiently in this condition. The initial magnetic permeability of particle assembly was nearly constant up to the Curie temperature. Though the initial magnetic permeability of flake shaped sendust decreased largely by the hydrothermal treatment, the ones of other metal materials decreased a little and of ferrite materials remained unchanged. Taking account of these results, we conclude that iron particle is suitable candidate for the tracer.