FORMATION RESISTIVITY MEASUREMENT SENSOR CONTAINED ONBOARD ADRILL BIT (RESISTIVITY IN BIT)

摘要

A method and apparatus (Fig. 8a) for obtaining a resistivity measurement of an earth formation surrounding a borehole in an MWD device uses an electrode (602) for injecting current into the earth formation and an electrode for obtaining a responsive signal from the borehole. The electrodes are located on the drill bit arm or blade (802). Measured resistivity values are obtained a t the location of the drill bit. Measurements can be taken in both oil-based m ud and water-based mud environments. Maximum or minimum resistivity can be used to best represent the resistivity of the surrounding formation.