Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
1999-09-07
2001-04-10
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
Reexamination Certificate
active
06216089
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of well logging and, more particularly, to well logging methods and apparatus for determining formation properties, such as conductivity, in high-contrast thin-layer formations or at high dip angles, with greater accuracy than prior methods. Still more particularly, this invention relates to an improved method for processing multiple voltage data obtained during logging with an induction array well tool and creating a depth tagged representation of resistivity or conductivity from a formulated difference of the voltage data. The invention has general application in the well logging art, but is particularly useful at a well site while logging.
2. Description of Related Art
Induction logging is a well-known form of electromagnetic logging used to make a determination of the conductivity (or its inverse, resistivity) profile of the earth formations surrounding a borehole. U.S. Pat. Nos. 3,340,464; 3,147,429; 3,179,879; 3,056,917; and 4,472,684 are illustrative of typical well logging tools that utilize the basic principles of induction logging.
Conventional induction logging tools or “sondes” include a transmitter and a receiver array consisting of a set of coils mounted on a support and axially spaced from each other in the direction of the borehole. The transmitting coil is energized by an alternating current, which in turn generates an electric field that induces eddy currents in the formation surrounding the borehole. The intensity of the eddy currents is proportional to the conductivity of the formation. The field generated in turn by these eddy currents induces an electromotive force in the receiving coil. Phase-locked detection, amplification, and digitization of this signal determines the amplitude and phase of the receiver voltage, usually expressed as a complex number (phasor voltage). By processing the receiver coil voltages, an evaluation of the formation conductivity profile is obtained. U.S. Pat. No. 5,157,605 (assigned to the present assignee) discloses an induction array well tool that may be used to develop voltage data for processing by the present invention.
Conventional techniques for evaluating the conductivity of formations have practical limitations. Neighboring layers in high-contrast (in terms of resistivity) thin-layer formations can corrupt the measurement results—known as shoulder effect. At high dip angles, horns and other artifacts are seen in the resistivity logs. Modeling and actual measurements have confirmed these effects. See B. Anderson et al.,
Response of
2-
MHz LWD Resistivity and Wireline Induction Tools in Dipping Beds and Laminated Formations,
SPWLA THIRTY-FIRST ANNUAL LOGGING SYMPOSIUM, Pp. 1-25, 1990. The cause of the horns is transverse magnetic (“TM”) coupling, which becomes important at high dip angles. The TM horns observed are useful to detect layer boundaries, but are detrimental for quantitative formation evaluation.
U.S. Pat. No. 5,041,975 describes a method for correcting data developed by the well tool of the '605 patent, to eliminate the effects of the borehole on the measured data. U.S. Pat. No. 5,184,079 describes a method for correcting logs, developed from a logging tool, disposed in a wellbore at a dip angle relative to the formation layers, to eliminate the effects of the dip angle on the resistivity logs. The applicability of this correction method is limited to dip angles less than about 45 degrees. Another method for correcting induction logs with high apparent dip angle effects was described by Barber et al.,
Interpretation of Multiarray Induction Logs in Invaded Formations at High Relative Dip Angles,
SPWLA THIRTY-NINTH ANNUAL LOGGING SYMPOSIUM, June, 1998. This method requires time-consuming model calculations, making it less desirable for operations at the well site while logging. An underlying criterion of the methods described by the '079 patent and Barber et al. is the requirement that the dip angle be known before the methods can be applied.
It is desirable to obtain a simplified method of processing data, acquired from a well tool, to correct for dip effect and neighboring layers in high-contrast thin-layer formations. Still further, it is desired to implement a data processing technique that is not restricted to piecewise constant formations and does not require prior knowledge of dip angles. Thus, there remains a need for a simplified process and apparatus that produces accurate conductivity profiles of unrestricted formations from data developed by a well tool.
SUMMARY OF THE INVENTION
A method and system are provided for producing a conductivity log unaffected by shoulder effect and dip from voltage data developed by a well tool when the tool is disposed in a borehole traversing a formation. The tool including a transmitter T
1
and a plurality of receiver pairs Rn (n>0).
In a first aspect of the invention, the voltage data developed by the well tool is accessed and boosted. Two-coil voltages are then reconstructed from the boosted voltage data. The reconstructed two-coil voltages are then processed and the conductivity log is produced from the processed two-coil voltages.
In a second aspect of the invention, a specific coil configuration is synthesized from the tool voltage data to provide a mutual balance condition to produce a formation conductivity log.
In a third aspect of the invention, a logging system is provided, including an well tool and an apparatus coupled to the tool where the apparatus is adapted to respond to voltage data developed by the receiver pairs Rn, for producing a conductivity log and recording the log on an output record medium.
REFERENCES:
patent: 3056917 (1962-10-01), Tanguy
patent: 3147429 (1964-09-01), Moran
patent: 3179879 (1965-04-01), Tanguy
patent: 3340464 (1967-09-01), Gouilloud
patent: 4472684 (1984-09-01), Schuster
patent: 4583045 (1986-04-01), Gianzero
patent: 5041975 (1991-08-01), Minerbo et al.
patent: 5115198 (1992-05-01), Gianzero et al.
patent: 5157605 (1992-10-01), Chandler et al.
patent: 5184079 (1993-02-01), Barber
patent: 5210691 (1993-05-01), Freedman et al.
patent: 5757191 (1998-05-01), Gianzero
Moran, J.H. and K.S. Kunz, “Basic Theory of Induction Logging and Application to Study of Two-Coil Sondes”,Geophysics, vol. XXVII, No. 6, Part 1 (Dec. 1962), pp. 829-858.
Anderson, Barbara et al., “Effect of Dipping Beds on the Response of Induction Tools”,SPE Formation Evaluation(Mar. 1988), pp. 29-36.
Clark, B. et al., “Electromagnetic Propagation Logging While Drilling: Theory and Experiment”, SPE Paper 18117, presented at the 63rdAnnual Technical Conference and Exhibition, Oct. 2-5, 1988, pp. 103-117.
Anderson, Barbara et al., “Response of 2-MHZ LWD Resistivity and Wireline Induction Tools in Dipping Beds and Laminated Formations”, SPWLA 31stAnnual Logging Symposium, Jun. 24-27, 1990, Paper A, pp. 1-25.
Hunka, J.F. et al., “A New Resistivity Measurement System for Deep Formation Imaging and High-Resolution Formation Evaluation”, SPE Paper 20559, presented at the 65thAnnual Technical Conference and Exhibition of the SPE, Sep. 23-26, 1990, New Orleans, pp. 295.
Meyer, W. Hal, et al., “A New Slimhole Multiple Propagation Resistivity Tool”, SPWLA 35thAnnual Logging Symposium, Jun. 19-22, 1994, Paper N.
Barber, Thomas D. et al., “Interpretation of Multiarray Induction Logs in Invaded Formations at High Relative Dip Angles”,The Log Analyst, vol. 40, No. 3 (May-Jun. 1999), pp. 202-217.
McElheny Jr. Donald E.
Schlumberger Technology Corporation
Segura Victor H.
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