Patent ID: 7202671
Filing Date: 2007-04-10
Classification: G01V

Abstract:
1. An instrument for measuring resistivity of Earth formations from within a conductive pipe inside a wellbore drilled through the formations, comprising: a plurality of housings connected end to end, the housings adapted to traverse the wellbore; at least one electrode on each housing, each electrode adapted to be placed in electrical contact with the inside of the pipe; a source of electrical current; a digital voltage measuring circuit; a first switch arranged to connect the source of electrical current between one of the electrodes and a current return at a selectable one of the top of the pipe and a location near the Earth's surface at a selected distance from the top of the pipe; a second switch arranged to connect selected pairs of the electrodes to the digital voltage measuring circuit, the pairs selected to make voltage measurements corresponding to selected axial distances and selected lateral depths in the Earth formations; and within at least one of the housings, at least one electromagnetic transmitter, at least one electromagnetic receiver and a control circuit adapted to selectively energize the at least one transmitter and to detect signals from the a least one electromagnetic receiver.