Patent ID: 8159227

Claim:
A method for making a directional resistivity measurement in a subterranean borehole, the method comprising: (a) rotating a directional resistivity tool in a borehole, the directional resistivity tool including (i) at least first and second transmitting antennae and (ii) at least one receiving antenna configured to receive an a substantially pure z-mode component of an electromagnetic wave, the receiving antenna being longitudinally spaced from the transmitting antennae, the first and second transmitting antennae configured to transmit corresponding substantially pure z-mode and x-mode electromagnetic waves; (b) causing the first transmitting antenna to transmit a first electromagnetic wave; (c) causing the receiving antenna to receive a substantially pure z-mode component of the first electromagnetic wave; (d) causing the second transmitting antenna to transmit a second electromagnetic wave; (e) causing the receiving antenna to receive a substantially pure z-mode component of the second electromagnetic wave; and (f) computing a ratio of the components received in (c) and (e).