TDEM forward focusing system for downhole use

摘要

A method and apparatus for estimating a parameter of interest of an earth formation ahead of a carrier within borehole. The method including estimating one or more functions based on received signals that may reduce the sum of the signals received by a first receiver, and estimating the parameter of interest based on signals received by one or more additional receivers by applying the one or more functions and, if necessary, a defocusing factor, such that reception of information from downhole of a selected downhole location is enhanced relative to reception of information uphole from the selected location. The apparatus including two or more transmitters, two or more receivers, and a processor to estimate one or more functions, and, based on these functions, the parameter of interest.

主权项

1. A method for estimating a parameter of interest relating to a subsurface formation, comprising:
generating a plurality of signals using at least two transmitters, wherein the plurality of signals are sequential such that the plurality of signals proceed from a transmitter of the at least two transmitters furthest from a selected location to a transmitter of the at least two transmitters closest to the selected location; estimating the parameter of interest by applying at least one focusing function to at least one receiver output from a receiver of a plurality of receivers, the at least one focusing function being estimated using transient electromagnetic signals received downhole by a first receiver of the plurality of receivers responsive to the plurality of signals, wherein the transient electromagnetic signals comprise a first signal and a second signal, and the at least one focusing function comprises a ratio of the first signal and the second signal; and using the parameter of interest to conduct further operations in the subsurface formation; and wherein the at least one focusing function is estimated to reduce a sum of the transient electromagnetic signals received by the first receiver to approximately zero.