Electrical anisotropy: its effect on well logs.

Abstract

The influence of electrical anisotropy on the response of a variety of electrode and induction devices is studied. Standard logging tools are considered where anisotropy can lead to some ambiguity in the interpretation of the measurements. Other tools are considered that are designed to be sensitive to anisotropy and yield a measurement of it. Our conclusions appear as the effects of anisotropy on standard logging tools and a proposal for a new tool that appears most promising for the measurement of anisotropy. This new tool is a micro-laterolog. The standard tools are somewhat insensitive to the vertical resistivity unless the dip is large except near bed boundaries. Among the standard tools, both the electrode and induction devices tend to yield the horizontal resistivity unless the spacings of the electrode device are small, of the order of the borehole diameter.-Authors