SYSTEM, APPARATUS, AND METHOD OF CONDUCTING BOREHOLE RESISTIVITY MEASUREMENTS

A logging-while-drilling tool is adapted for incorporation with a drill stri ng having a longitudinal axis. The drill string is further adapted for drilling a wellbo re penetrating a geological formation. The drilling tool includes a tool body having a centra l axis disposed in parallel relation with the longitudinal axis of the drill string and an external, circumferential surface spaced radially outward from the central axis. The tool also include s a measurement apparatus for measuring resistivity of a borehole fluid in the wellbore. The measurement apparatus has an electrode array including a current emitting electrode disposed on the circumferential surface. The current emitting electrode is adapted to emit current into a target region of the wellbore spaced laterally between the circumferential surface and the walls of the wellbore. Further, a current receiving electrode is disposed on the circumferential surface and spaced apart from the current emitting electrode. The current receiving electrode is adapted to receive current propagated from the current emitting electrode into the targ et region. The electrode array occupies an arcuate section of the circumferential surface that extends less than about 180.degree. about the central axis.