Patent ID: 8390295
Filing Date: 2013-03-05
Classification: G01V

Abstract:
1. An apparatus for measuring a resistivity parameter of an earth formation, the device comprising: at least one measurement electrode that emits a measurement current into the formation, the measurement electrode being electrically connected to a first electrical source that is configured to apply at least one of a current and a voltage to the measurement electrode; at least one guard electrode that emits a guard current for focusing the measurement current; a shielding electrode interposed between the at least one guard electrode and the at least one measurement electrode, the shielding electrode being electrically connected to an electric measuring device for measuring current in the shielding electrode and electrically connected to a second electrical source that is configured to apply at least one of a current and a voltage to the shielding electrode, the second electrical source independent from the first electrical source, the first and second electrical sources being adjustable in response to a current measured by the electric measuring device, and the guard electrode being electrically connected to a third electrical source independent of the first and second electrical sources; at least one return electrode for receiving current emitted from at least one of the measurement electrode, the shielding electrode and the guard electrode; insulators positioned between (i) the at least one measurement electrode and the shielding electrode, (ii) the shielding electrode and the at least one guard electrode and (iii) the at least one measurement electrode, the at least one guard electrode and the return electrode; and a processor configured to independently adjust the first electrical source and the second electrical source in response to a current measured by the electric measuring device to minimize a current flow through the shielding electrode.