Multi-frequency focusing for MWD resistivity tools
AssigneeBaker Hughes Incorporated
InventorsLeonty A. Tabarovsky, Alexandre N. Bespalov, Stanislav W. Forgang, Michael B. Rabinovich
Life of this patent
Estimating the term…
Abstract
An induction logging tool is used on a MWD bottom hole assembly. Due to the finite, nonzero, conductivity of the mandrel, conventional multi frequency focusing (MFF) does not work. A correction is made to the induction logging data to give measurements simulating a perfectly conducting mandrel. MFF can then be applied to the corrected data to give formation resistivities.
Claims43
A method of determining a resistivity of an earth formation comprising:
- (a) conveying a resistivity measuring instrument having at least one transmitter and at least one receiver spaced apart from said at least one transmitter;
- (b) activating said at least one transmitter at a number m of frequencies having selected associated values (ωi, i=1,m) and inducing signals in said at least one receiver, said induced signals indicative of said resistivity of said earth formation;
- and
- (c) applying a multifrequency focusing (MFF) to said induced signals to give a focused signal;
- wherein said associated values are selected to increase linear independence of vectors defined at least in part by said associated values and a number of terms n of said MFF.
An apparatus for determining a resistivity of an earth formation comprising:
- (a) a resistivity measuring instrument conveyed in a borehole in said earth formation, said resistivity measuring instrument having:
- (A) a mandrel (housing),
- (B) at least one transmitter on said mandrel which operates at a number m of frequencies having selected associated values (ωi, i=1,m) and produces electromagnetic fields in said earth formation, and
- (C) at least one receiver spaced apart from said at least one transmitter which produce signals resulting from interaction of said electromagnetic fields with said earth formation;
- and
- (b) a processor which applies a multifrequency focusing (MFF) to said produced signals to give a focused signal;
- wherein said associated values are selected to increase linear independence of vectors defined by said associated values and a number of terms n of said MFF.
A method of estimating a resistivity of an earth formation comprising:
- (a) conveying a resistivity measuring tool conveyed into a borehole in the earth formation, the resistivity measuring tool having a mandrel (housing) with a finite, non-zero conductivity:
- (b) operating a transmitter on said resistivity measuring tool at a plurality of frequencies;
- (c) receiving signals at least one receiver on said resistivity measuring tool, said at least one receiver axially separated from said transmitter, said signals indicative of said resistivity of said earth formation;
- and
- (d) processing said received signals and estimating the resistivity of the earth formation, said processing taking into said account finite, non-zero conductivity of said mandrel.
An apparatus for estimating a resistivity of an earth formation, said apparatus comprising:
- a) a mandrel (housing) on a measurement—while-drilling (MWD) tool, said mandrel having a finite non-zero conductivity having a finite, non-zero conductivity;
- b) a transmitter and at least one receiver spaced apart from said transmitter on said MWD tool, said transmitter operating at a plurality of frequencies and said at least one receiver receiving signals indicative of said resistivity;
- and
- c) a processor which processes said received signals and estimates said resistivity, said determination accounting for said finite non-zero conductivity.
Dependencies are inferred from the claim text.