Transient tri‐axial induction measurements: Apparent dip and apparent anisotropy

Abstract

The transient tri‐axial induction log can read formation resistivity deep with a short transmitter‐receiver offset. Interpretation of the transient data is straightforward and the formation can be imaged using the time‐sequential voltage responses at a receiver or the time‐dependent apparent conductivity and/or apparent dip. The dip and anisotropy of an anisotropic formation are algebraically derived from the transient tri‐axial induction data in a homogeneous anisotropic formation. The time‐dependent apparent dip and apparent anisotropy are algebraically defined from the transient tri‐axial induction measurements in layered formations. The apparent dip yields the true dip in an anisotropic formation as well as in layered formations, though it yields the zero dip in an isotropic formation. The apparent anisotropy yields the true anisotropy of the layer around the induction tool at early time and the macroscopic anisotropy within a larger volume of investigation at later time. The distance to the layer interface is identified by the transition time where the apparent dip and the apparent anisotropy change the values.