Acoustic Communications Network with Frequency Diversification

Patent metadata

Field	Value
Publication number	US-2016258285-A9
Application number	US-201514818270-A
Country	US
Kind code	A9
Filing date	Aug 4, 2015
Priority date	Aug 3, 2014
Publication date	Sep 8, 2016
Grant date	—

Abstract

An acoustic communications network includes acoustic modems that exchange messages on an acoustic communications medium, such as tubing deployed in a wellbore. The acoustic communications medium is characterized by an acoustic transfer function having a plurality of passbands and a plurality of stopbands. The messages are communicated by encoding the message into a plurality of symbols representing the message and distributing the plurality of symbols across a bandwidth of a wideband acoustic signal that spans at least one passband and at least one stopband of the acoustic transfer function.

First claim

1 . A method of communicating in a borehole, comprising:
transmitting a message via an acoustic communications medium between acoustic modems deployed in the borehole, the acoustic communications medium characterized by an acoustic transfer function having a plurality of passbands and a plurality of stopbands, wherein transmitting includes:
encoding the message into a plurality of symbols representing the message; and
distributing the plurality of symbols over a bandwidth of a wideband acoustic signal, wherein the bandwidth spans at least one passband and at least one stopband of the acoustic transfer function; and
receiving and processing the wideband acoustic signal to recover the message from the plurality of symbols distributed over the bandwidth.

2 . The method as recited in claim 1 , wherein the plurality of symbols are distributed over the bandwidth using Orthogonal Frequency Division Multiplexing (OFDM).

3 . The method as recited in claim 1 , wherein the message is encoded using Forward Error Correction (FEC).

4 . The method as recited in claim 2 , wherein the message is encoded using Forward Error Correction (FEC).

5 . The method as recited in claim 4 , wherein the message is recovered from the plurality of symbols using maximal combining ratio coding.

6 . The method as recited in claim 1 , further comprising selecting the bandwidth of the wideband acoustic signal before deploying the acoustic modems in the borehole.

7 . The method as recited in claim 6 , further comprising using the same selected bandwidth to transmit messages between all the acoustic modems deployed in the wellbore.

8 . A method of transmitting messages in an acoustic communications network, comprising:
transmitting a first message in a first wideband acoustic signal from a first acoustic modem in a network of acoustic modems deployed along an acoustic transmission medium, the message being addressed to a second acoustic modem and containing information to be re-transmitted by the second acoustic modem; determining, by a third acoustic modem, whether the second modem has received the first message; and, if not transmitting, by the third acoustic modem, a second message containing the information that was to be re-transmitted by the second acoustic modem.

9 . The method as recited in claim 8 , wherein determining whether the first message has been received by the second acoustic modem comprises:
receiving, by the third acoustic modem, the first message; and detecting whether the second acoustic modem transmits a message before elapse of a predetermined time period, and, if not, inferring that the second acoustic modem did not receive the first message.

10 . The method as recited in claim 9 , wherein determining whether the first message has been received by the second acoustic modem comprises:
upon receipt of the first message by the third acoustic modem, entering by the third acoustic modem a listening mode for the predetermined time period; and transmitting the second message upon the elapse of the predetermined time period based on inferring that the second acoustic modem did not receive the first message.

11 . The method as recited in claim 8 , wherein transmitting the first message comprises:
encoding the first message into a plurality of symbols representing the first message; and distributing the plurality of symbols across a bandwidth of the first wideband acoustic signal, wherein the bandwidth spans at least one passband and at least one stopband of an acoustic frequency response of the acoustic transmission medium.

12 . The method as recited in claim 11 , wherein transmitting the second message comprises:
encoding the second message into a plurality of symbols; and distributing the plurality of symbols across a bandwidth of a second wideband acoustic signal, wherein the bandwidth of the second wideband acoustic signal and the bandwidth of the first wideband acoustic signal are the same bandwidth.

13 . The method as recited in claim 12 , wherein the first message and the second message are encoded using Forward Error Correction (FEC).

14 . The method as recited in claim 12 , wherein the plurality of symbols of the first message and the plurality of symbols of the second message are distributed across the same bandwidth using Orthogonal Frequency Division Multiplexing (OFDM).

15 . The method as recited in claim 8 , wherein the third acoustic modem is deployed at a location along the acoustic transmission medium that is located between the first acoustic modem and the second acoustic modem.

16 . A system for performing a downhole operation in a wellbore, comprising:
a control and telemetry system located at a surface to control and monitor a downhole operation; downhole equipment located in the wellbore to observe a parameter of interest associated with the downhole operation; first and second acoustic modems coupled to an acoustic transmission medium at respective locations extending between the control and telemetry system and the downhole equipment, wherein the acoustic transmission medium has an acoustic frequency response comprising passbands and stopbands, wherein in response to receipt of a message directed to the downhole equipment, the first acoustic modem generates information representing the message, distributes the information across a bandwidth that spans at least one passband and at least one stopband of the acoustic frequency response to generate a first wideband signal, and acoustically transmits the first wideband signal to the second acoustic modem on the acoustic transmission medium.

17 . The system as recited in claim 16 , wherein the second acoustic modem receives the first wideband signal and processes the first wideband signal to recover the message.

18 . The system as recited in claim 17 , wherein, in response to the message, the second acoustic modem retrieves from the downhole equipment data representative of the parameter of interest and transmits a second wideband signal containing information corresponding to the retrieved data for receipt by the control and telemetry system, wherein the information contained in the second wideband signal is distributed across the bandwidth.

19 . The system as recited in claim 18 , further comprising
a third acoustic modem coupled to the acoustic transmission medium, wherein upon receipt of a wideband acoustic signal that is not addressed to the third acoustic modem, the third acoustic modem monitors the acoustic transmission medium for a predetermined time period to determine whether an addressed acoustic modem has transmitted a message, and, if not, upon elapse of the predetermined time period, the third acoustic modem transmits a wideband acoustic signal containing information that should have been transmitted in the message by the addressed acoustic modem.

20 . The system as recited in claim 19 , wherein the third acoustic modem is coupled to the acoustic transmission medium at a location between the first acoustic modem and the second acoustic modem.

Assignees

• Schlumberger Technology Corp

Inventors

• Croux Arnaud

Classifications

• E21B47/16 Primary

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

• H04B11/00

  Transmission systems employing ultrasonic, sonic or infrasonic waves · CPC title