Decision Feedback Equalization in Mud-Pulse Telemetry

Abstract

A decision feedback equalizer (DFE) structure which uses a reference signal based adaptive equalizer as forward filter and a blind adaptive equalizer as feedback filter is used for surface processing of mud pulse telemetry data.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

For detailed understanding of the present invention, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein:

FIG. 1 (prior art) is a schematic illustration of a drilling system suitable for use with the present invention;

FIGS. 2 a-2c (prior art) is a schematic of an oscillating shear valve suitable for use with the present invention;

FIG. 3 is a flow chart of the processing used on signals received at a surface location;

FIG. 4 is an illustration of model for signal propagation at surface;

FIG. 5 shows a decision feedback equalizer structure used for surface signal processing;

FIG. 6 shows the concept of applying an equalizer;

FIG. 7 illustrates the methodology of adaptive equalization processing; and

FIG. 8 shows a flow chart of an adaptive feedback equalizer.

Claims

1. A method of communicating a signal through a fluid in a borehole between a downhole source location and a surface location, the method comprising: (a) generating a message signal at the downhole location and receiving a first signal at the surface location responsive to the message signal;(b) determining a transfer function between the downhole location and a surface location; and(c) using the determined transfer function and an equalization method including a feedback equalizer for providing an estimate of the message signal.

2. The method of claim 1 further comprising determining the transfer function by: (i) generating a reference signal at the downhole location;(ii) making an additional measurement at the surface location responsive to the reference signal; and(iii) determining from the additional measurement and the reference signal the transfer function.

3. The method of claim 2 wherein the reference signal comprises a chirp signal.

4. The method of claim 3 wherein the equalization method further comprises using a filter selected from the group consisting of: (i) a finite impulse response (FIR) filter, and (ii) and infinite impulse response (IIR) filter.

5. The method of claim 4 further comprising estimating coefficients of the filter by: (i) generating a reference signal at the downhole location;(ii) measuring an additional signal at the surface location responsive to the reference signal; and(iii) minimizing a cost function based on the reference signal and the additional signal.

6. The method of claim 1 wherein providing the estimated message signal further comprises a demodulation.

7. The method of claim 6 wherein the demodulation is subsequent to the equalization.

8. The method of claim 7 further comprising an additional equalization subsequent to the demodulation.

9. The method of claim 8 wherein the additional equalization further comprises a feedback equalization.

10. The method of claim 1 wherein the equalization method further comprises using a stochastic gradient algorithm.

11. The method of claim 1 wherein the equalization method further comprises using at least one of: (i) a Godard algorithm, (ii) a Sato algorithm, (iii) a Benveniste-Goursat algorithm, and (iv) a Stop-and-go algorithm.

12. The method of claim 1 further comprising displaying an estimate of the property at the surface location.

13. The method of claim 1 wherein the message signal is indicative of at least one of (i) an operating condition of a bottomhole assembly, and (ii) a location and orientation of the borehole.

14. An apparatus for evaluating an earth formation, the apparatus comprising: (a) a formation evaluation sensor configured to be conveyed in a borehole and make a measurement indicative of the property of the earth formation;(b) a message source configured to generate a message signal in a borehole fluid at a downhole location;(c) a sensor at a surface location configured to receive a first signal responsive to the message signal; and(d) a processor configured to: (A) determine a transfer function between the downhole location and a surface location; and(B) use the determined transfer function and an equalization method including a feedback equalizer for providing an estimate of the message signal.

15. The apparatus of claim 14 wherein the message source is further configured to generate a reference signal; and processor is further configured to determine the transfer function by using the reference signal and an additional measurement at the surface location responsive to the reference signal.

16. The apparatus of claim 15 wherein the reference signal comprises a chirp signal.

17. The apparatus of claim 14 wherein the equalizer further comprises at least one of: (i) a finite impulse response (FIR) filter, and (ii) an infinite impulse response (IIR) filter.

18. The apparatus of claim 14 wherein the processor is further configured to provide the estimated message signal by using a demodulation.

19. The apparatus of claim 18 wherein the processor is configured to apply the demodulation subsequent to the equalization.

20. The apparatus of claim 19 wherein the processor is further configured to apply an additional equalization subsequent to the demodulation.

21. The apparatus of claim 14 further comprising a bottomhole assembly conveyed on a drilling tubular; the bottomhole assembly including the formation evaluation sensor and the message source.

22. The apparatus of claim 14 wherein the processor is further configured to display an estimate of the property at the surface location.

23. The apparatus of claim 14 wherein the message signal is indicative of at least one of: (i) an operating condition of a bottomhole assembly, and (ii) a location and orientation of the borehole the apparatus further comprising a sensor configured to measure the at least one of (i) an operating condition of a bottomhole assembly, and (ii) a location and orientation of the borehole.