Determination of Dip and Anisotropy from Multi-frequency Tri-axial Induction Measurements

The tri-axial (or multi-component) induction log is used to measure not only the resistivity anisotropy of an anisotropic formation but also the relative dip of the tool with respect to the formation. When the tri-axial induction log is run at multiple frequencies, multi-frequency focusing can be applied to the measurements. The apparent dip and the apparent anisotropy are algebraically deflned from the frequency-focused tri-axial induction measurements. The apparent dip gives the true dip in thinly bedded formations, but a smaller dip than the true dip in a thick anisotropic bed when the anisotropy is small (the anisotropy efiect). The apparent anisotropy gives the true anisotropy in thick anisotropic formations but is afiected by the shoulder bed anisotropy when the formation is not thick (the shoulder bed efiect).