Borehole fluid resistivity measurements

摘要

A downhole tool (820) having a longitudinal axis a central axis (860) and an external, circumferential surface (818) spaced radially outward from the central axis. The tool also includes a measurement apparatus for measuring resistivity of a borehole fluid (110) in the wellbore (106). The measurement apparatus has an electrode array (130) 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 (112a) 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 from the current emitting electrode into the target region. The electrode array occupies an arcuate section of the circumferential surface that extends less than about 180{ about the central axis. The tool may be a logging-while-drilling tool (LWD) attached to a drill string. A second electrode array (830) may be included to measure resistivity of fluid being pumped into the wellbore.