Downhole telemetry systems and methods with time-reversal pre-equalization

Patent metadata

Field	Value
Publication number	US-9822634-B2
Application number	US-201214380005-A
Country	US
Kind code	B2
Filing date	Feb 22, 2012
Priority date	Feb 22, 2012
Publication date	Nov 21, 2017
Grant date	Nov 21, 2017

Abstract

Specific embodiments of disclosed downhole telemetry systems and methods employ time-reversal pre-equalization. One downhole telemetry system embodiment includes an acoustic transducer and a digital signal processor. The acoustic transducer transmits an acoustic signal to a distant receiver via a string of drillpipes connected by tool joints. The digital signal processor drives the acoustic transducer with an electrical signal that represents modulated digital data convolved with a time-reversed channel response. Due to the use of time-reversal pre-equalization, the received signal exhibits substantially reduced intersymbol interference.

First claim

What is claimed is:

1. A downhole telemetry system that comprises:
an acoustic transducer that transmits an acoustic signal to a receiver via a string of drillpipes connected by tool joints such that the acoustic signal is transmitted along the string of drillpipes one drillpipe after another; and
a digital signal processor that drives the acoustic transducer with an electrical signal that represents modulated digital data convolved with a time-reversed channel response corresponding to the transmission along the string of drillpipes one drillpipe after another,
wherein the digital signal processor determines the time-reversed channel response based on a model, parameters of the model including an estimated number of drillpipes in the string.

2. The system of claim 1 , wherein the digital signal processor convolves a modulated signal with the time-reversed channel response to obtain said electrical signal.

3. The system of claim 2 , wherein the acoustic transducer is part of a transceiver, and wherein the digital signal processor processes received signals to determine the time-reversed channel response.

4. The system of claim 1 , wherein the acoustic transducer is part of a transceiver, and wherein the digital signal processor derives from a received signal a representation of each channel symbol, wherein the digital signal processor stores said representations, and wherein the digital signal processor generates said electrical signal by overlapping and adding said representations in a sequence.

5. The system of claim 1 , wherein the digital data is modulated with frequency-shift keying.

6. The system of claim 1 , wherein the digital data is modulated with amplitude-shift keying.

7. The system of claim 1 , wherein the digital data is modulated with phase-shift keying, quadrature amplitude modulation, or orthogonal frequency division multiplexing.

8. A downhole telemetry method that comprises:
generating an electrical signal that represents modulated digital data convolved with a time-reversed response of an acoustic channel that includes a string of drillpipes connected by tool joints, the time-reversed response corresponding to transmission along the string of drillpipes one drillpipe after another;
driving an acoustic transducer with the electrical signal to communicate the modulated digital data along the string of drillpipes one drillpipe after another to a receiver; and
determining the time-reversed response using a model, parameters of the model including a variable number of drillpipes in the acoustic channel.

9. The method of claim 8 , wherein said generating includes convolving a modulated signal with a channel response and time-reversing the result to obtain said electrical signal.

10. The method of claim 8 , wherein said generating includes convolving a modulated signal with the time-reversed response to obtain said electrical signal.

11. The method of claim 10 , further comprising:
processing received signals to extract a determined channel response; and
storing a time-reversed version of the determined channel response.

12. The method of claim 8 , further comprising:
extracting from a received signal a representation of each channel symbol;
storing a time-reversed version of each channel symbol representation; and
assembling a sequence of said stored channel symbol representations.

13. The method of claim 8 , wherein the modulated digital data is frequency-shift keyed.

14. The method of claim 8 , wherein the modulated digital data is amplitude-shift keyed.

15. The method of claim 8 , wherein the modulated digital data is phase-shift keyed, quadrature amplitude modulated, or modulated via orthogonal frequency division multiplexing.

16. A downhole telemetry method that comprises:
generating an electrical signal that represents modulated digital data convolved with a time-reversed response of an acoustic channel that includes a string of drillpipes connected by tool joints, the time-reversed response corresponding to transmission along the string of drillpipes one drillpipe after another;
driving an acoustic transducer with the electrical signal to communicate the modulated digital data along the string of drillpipes one drillpipe after another to a receiver;
determining the time-reversed response using a model, parameters of the model including a variable number of drillpipes in the acoustic channel;
obtaining a frequency-domain channel response and storing the frequency-domain channel response in memory;
generating each possible modulated channel symbol;
frequency transforming each modulated channel symbol;
multiplying each frequency transformed channel symbol with the frequency-domain channel response to obtain corresponding products;
inverse transforming the products to obtain time-domain convolutions;
time-reversing the time-domain convolutions to obtain channel symbol representations; and
assembling the channel symbol representations into a sequence to obtain said electrical signal.

17. The method of claim 16 , wherein the modulated channel symbols are frequency-shift keyed representations of a binary 0 and a binary 1.

Assignees

• Gao Li
• Halliburton Energy Services Inc

Inventors

• Gao Li

Classifications

• E21B47/16 Primary

  through the drill string or casing {, e.g. by torsional acoustic waves} · CPC title