Numerical analysis of near‐borehole and anisotropeic layer effects on the response of multicomponent induction logging tools

Abstract

We present finite‐difference simulation results that lend new insight into the behavior of multicomponent induction logging tools when in the presence of anisotropic layers, boreholes, and invasion zones. We use four independent models to investigate multicomponent tool properties as well as typical magnetic field responses. In addition, model variations with respect to formation dip angle, layer geometry, and conductivity provide data about the effects of geological variation on the multicomponent responses. Simulations suggest a coaxial tool configuration senses a depth of twice the source–receiver offset, although this depth is reduced to the source–receiver offset with coplanar configurations. Numerical responses in the presence of transversely isotropic layers provide evidence that anisotropy can have a measurable effect on both coaxial and coplanar magnetic fields; these effects increase as layer dip increases. Sensitivity analyses substantiate these numerical results. An investigation of tool responses to varying borehole and invasion zone conductivities and diameters demonstrates that the coplanar tool orientation is much more sensitive to near‐borehole variations than the coaxial configuration. A frequency‐differencing technique is presented to mitigate unwanted borehole‐induced bias in multicomponent data; however, drawbacks include decreased signal strength and possible geological signal destruction.

Modeling and analysis of the response of a triaxial, frequency-domain electromagnetic induction sensor to a buried linear conductor

“…Sensors are becoming increasingly more sophisticated and one key advancement is the use of multicomponent receivers ͑Kriegshäuser et al, 2000;Rosthal et al, 2003͒. Multicomponent sources and receivers have been studied extensively for borehole applications where they have shown their value in probing anisotropic formations ͑e.g., see Tompkins et al, 2004, and the references therein͒. Smith and Keating ͑1996͒ have illuminated the benefits of multicomponent sensors for airborne, time-domain EMI investigations.…”

Development and anlysis of fast, approximate 3D Algorithms for interpretation of multi-component induction logging data

“…This is a result of the near-well sensitivity changing as the angle between the tool axis and the conductivity tensor changes (Lu and Alumbaugh, 2001;Tompkins et al, 2004). As a result of the anisotropy altering the total field amplitude relative to the isotropic case, assumptions used in inverting multi-component data for near-well formation properties can result in error.…”