Dean M. Homan

Inductive conductivity tensor measurement for flowline or material samples

Present-day galvanic-based electrical conductivity measurements are hampered by limitations and necessary corrections, especially in the domain of geological core analysis. Low-accuracy techniques such as crucible, two-electrode, and four-electrode are constricted by current-path requirements, while high-accuracy techniques are time consuming and have limited domains of applicability. We present a novel apparatus capable of electrical conductivity tensor measurements in a noninvasive, noncontact, inductive manner with resolution from 5 mS/m. Inspired by the triaxial induction logging technology appearing in the oil patch today, our apparatus is naturally applicable in a novel way not only to anisotropic geological core analysis but also to arbitrary material samples and flowline systems.

Eccentricity Effect of a Transverse Magnetic Dipole In a Conductive Borehole In a Homogeneous Isotropic Formation

An experimental three-coil induction sonde with tilted coils was built to study and then minimize its borehole effect. When such a tool is placed in a conductive borehole and eccentered in a direction perpendicular to the dipole moment of the sensors a huge borehole signal results. This is due to the excitation of a large axial current associated with the TM01 mode. The measured response of a transverse or tilted magnetic dipole (TMD) three-coil sonde is as much as a hundred times greater than the eccentered effect seen in a comparable three-coil longitudinal magnetic dipole (LMD) induction sonde. It is this striking response to the borehole that must be understood and then minimized without degradation to the formation response. We have altered the conventional induction tool design to eliminate this borehole current and instead route it through the tool rather than the external environment. The result is a dramatic decrease in the borehole effect. This manuscript will present results of both measurements and calculations of the response of the tilted magnetic dipole tool to eccentering in a conductive borehole surrounded by a less conductive formation, composed of a 23,000-gallon tank with a 14-foot diameter. For completeness a resistive borehole surrounded by a conductive formation is also shown. The measured response of the tilted three-coil sonde due to eccentering in the above mentioned formations agree well with the model results from an analytic code.

Triaxial induction tool with electrode sleeve: A study of its response to borehole eccentricity

We developed a finite difference (FD) code to model the response of a multiple-spacing triaxial array induction tool with a multiple-electrode type sleeve in a homogeneous medium and decentralized within a borehole in a homogeneous medium. The electrode sleeve reduces the response of the transverse couplings to eccentering in a conductive borehole. The model response was carefully checked for grid refinement, while attempting to minimize run time. Many details of the electrode sleeve geometry were studied, using this code, which led to the final electrode sleeve design. The comparison between the FD code and two other independent codes is quantitative. Good agreement is found between measurements and calculations.