Patent ID: 7095233

Claim:
A logging-while-drilling tool adapted for incorporation with a drill string having a longitudinal axis, the drill string being adapted for drilling of a wellbore penetrating a geological formation and the wellbore having an all-around wall, said drilling tool comprising: a tool body having a central axis disposed in generally parallel relation with the longitudinal axis of the drill string and a circumferential surface spaced radially outward from said central axis; and a measurement apparatus for measuring resistivity of a borehole fluid in the wellbore, said measurement apparatus having an electrode array including a current emitting electrode disposed on said circumferential surface, said current emitting electrode being adapted to emit current into a target region of the wellbore spaced laterally between said circumferential surface and the wall of the wellbore; and a current receiving electrode disposed on said circumferential surface and spaced apart from said current emitting electrode, said current receiving electrode being adapted to receive current propagated from said current emitting electrode into the target region, wherein said electrode array occupies an arcuate section of said circumferential surface, wherein said electrode array is configured such that rent emitted from said current emitting electrode and received by said current receiving electrode traverses a current path through the target region that has a lateral or circumferential component that extends less than about 180° about said central axis.