System and Method for Measurement While Drilling Telemetry

Abstract

A system for transmitting information in a well comprises a tubular string disposed in the well and having a drilling fluid flowing therethrough. A pulser is disposed in the tubular string and transmits a pulse synchronization marker comprising a chirp signal. A surface controller, acting under programmed instructions, detects the chirp signal adjusts a signal decoding technique based on the detected chirp signal.

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, wherein:

FIG. 1 shows an exemplary drilling system according to one embodiment of the present invention;

FIG. 2 is a flow chart of a drilling fluid telemetry system according to one embodiment of the present invention;

FIG. 3 is a sketch of an exemplary Non-Return to Zero (NRZ) encoding timeline;

FIG. 4 shows an exemplary continuous wave, frequency shift key (FSK) pulse signal and the corresponding NRZ baseband signal;

FIG. 5 shows an exemplary amplitude shift key (ASK) signal and the corresponding NRZ baseband signal;

FIG. 6 shows an exemplary continuous phase modulated (CPM) signal and the corresponding digital bits;

FIG. 7 shows an exemplary dual pressure transducer detection layout;

FIG. 8 shows an exemplary transmission stream comprising synchronization frames and unequal data frames;

FIG. 9 shows details of one embodiment of a synchronization frame;

FIG. 10 shows a representation of a chirp signal as a function of frequency versus time and as a function of amplitude versus time;

FIG. 11 shows an autocorrelation function of a chirp signal in the time domain;

FIG. 12 shows an autocorrelation of a chirp signal in the frequency domain; and

FIG. 13 shows a block diagram of a channel transfer function.

Claims

1. A system for communicating data from a downhole location to a surface location, the system comprising: (a) a bottomhole assembly (BHA) conveyed in a borehole in the earth formation;(b) a signal source on the BHA, the signal source configured to produce a pulsed variation in a fluid in a borehole, the pulsed variation including a bitstream indicative of the data to be communicated;(c) at least one sensor near a surface location in the borehole configured to produce a signal responsive to the pulsed variation; and(d) at least one processor configured to: (A) estimate from the signal the produced pulsed variation, and(B) use the estimated pulsed variation to estimate the data.

2. The system of claim 1 wherein the data to be communicated is indicative of an output of a formation evaluation (FE) sensor on the BHA.

3. The system of claim 1 wherein the data to be communicated is indicative of an operating condition of the BHA, the system further comprising a sensor configured to make a measurement about the operating condition.

4. The system of claim 1 wherein the data to be communicated is survey information about the borehole, the system further comprising a surveying device configured to produce the survey information.

5. The system of claim 1 wherein the signal source is selected from the group consisting of: (i) an oscillating valve, (ii) a poppet type pulser, and (iii) a siren.

6. The system of claim 1 wherein the pulsed variation further comprises at least one of: (i) a pressure pulse, and (ii) a flow rate pulse.

7. The system of claim 1 wherein the bitstream further comprises a synchronization marker and wherein the processor is further configured to use the synchronization marker in processing of the signal.

8. The system of claim 1 wherein the pulsed variation further comprises a modulation selected from: (i) a pulse amplitude modulation, (ii) frequency shift keying, (iii) amplitude shift keying, (iv) phase shift keying and (v) continuous phase moderation.

9. The system of claim 1 wherein the sensor comprises at least one of: (i) a pressure sensor, and (ii) a flow rate sensor.

10. The system of claim 1 wherein the at least one processor is further configured to do at least one of: (i) removing noise components, and (ii) perform a channel equalization.

11. The system of claim 1 further comprising a downhole processor configured to perform a data compression operation to the data.

12. The system of claim 1 wherein the at least one processor is further configured to perform a decompression.

13. The system of claim 1 wherein the sensor at the surface location further comprises at least two longitudinally-spaced transducers.

14. The systems of claim 7 wherein the synchronization marker further comprises at least one chirp signal.

15. The system of claim 7 wherein the synchronization marker further comprises a plurality of chirp signals embedded at known points.

16. A method of communicating data from a downhole location to a surface location, the method comprising: (a) conveying a bottomhole assembly (BHA) conveyed in a borehole in the earth formation;(b) activating a signal source on the BHA to produce a pulsed variation in a fluid in a borehole, the pulsed variation including a bitstream indicative of the data to be communicated;(c) using at least one sensor near a surface location in the borehole to produce a signal responsive to the pulsed variation;(d) estimating from the signal the produced pulsed variation, and(e) using the estimated pulsed variation to estimate the data.

17. The method of claim 1 wherein the data to be communicated is indicative of at least one of: (i) a property of the earth formation, (ii) operating condition of the BHA, and (iii) survey information about the borehole.

18. The method of claim 16 wherein producing the pulsed variation further comprises producing at least one of: (i) a pressure pulse, and (ii) a flow rate pulse.

19. The method of claim 16 further comprising using a synchronization marker in the bitstream, the method further comprising using the synchronization marker in processing of the signal.

20. The method of claim 16 wherein producing the pulsed variation further comprises performing a modulation encoding at least one of: (i) a pulse amplitude modulation, (ii) frequency shift keying, (iii) amplitude shift keying, (iv) phase shift keying and (v) continuous phase moderation.

21. The method of claim 16 wherein using the sensor further comprises using at least one of: (i) a pressure sensor, and (ii) a flow rate sensor.

22. The method of claim 16 further comprising at least one of: (i) removing noise components, and (ii) perform a channel equalization.

23. The method of claim 16 further comprising performing a data compression operation prior to the signal source producing the pulsed variation.

24. The method of claim 16 further comprising performing a decompression at the surface location.

25. The method of claim 16 wherein using the sensor at the surface location further comprises using at least two longitudinally-spaced transducers.

26. The method of claim 19 wherein the synchronization marker further comprises a plurality of chirp signals embedded at known points.

27. A computer-readable medium for use with a system for communicating data from a downhole location to a surface location, the system comprising: (a) a bottomhole assembly (BHA) conveyed in a borehole in the earth formation;(b) a signal source on the BHA, the signal source configured to produce a pulsed variation in a fluid in a borehole, the pulsed variation including a bitstream indicative the data to be communicated; and(c) a sensor near a surface location in the borehole configured to produce a signal responsive to the pulsed variation;the medium comprising instructions which enable a processor to:(d) estimate from the signal the produced pulsed variation, and(e) use the estimated pulsed variation to estimate the data.

28. The medium of claim 27 further comprising at least one of: (i) a ROM, (ii) an EPROM, (iii) an EAROM, (iv) a flash memory, and (v) an optical disk.