Transmitter and receiver synchronization for wireless telemetry systems

Abstract

An acoustic modem for communication in a network of acoustic modems via a communication channel. The acoustic modem comprises a transceiver assembly, transceiver electronics, and a power supply. The transceiver assembly is adapted to convert acoustic messages into electrical signals. The transceiver electronics is provided with transmitter electronics and receiver electronics. The transmitter electronics cause the transceiver assembly to send acoustic signals into the communication channel. The receiver electronics comprises at least one microcontroller adapted to execute instructions to (1) enable the receiver electronics to receive electrical signals indicative of the acoustic message from at least one other acoustic modem via the transceiver assembly, (2) estimate a carrier frequency of the electrical signals by analyzing an estimation frame of the electrical signals, (3) estimate a starting time of a data frame of the electrical signals by synchronizing with a synchronization frame of the acoustic message in parallel with at least two bit rates, and (4) decode the data frame. The power supply supplies power to the transceiver assembly and the transceiver electronics.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]Not applicable.TECHNICAL FIELD[0002]The present invention relates to telemetry systems for use with installations in oil and gas wells or the like. In particular, the present invention relates to the transmission of data and control signals between a location down a borehole and the surface, or between downhole locations themselves.BACKGROUND ART[0003]One of the more difficult problems associated with any borehole is to communicate measured data between one or more locations down a borehole and the surface, or between downhole locations themselves. For example, in the oil and gas industry it is desirable to communicate data generated downhole to the surface during operations such as drilling, perforating, fracturing, and drill stem or well testing; and during production operations such as reservoir evaluation testing, pressure and temperature monitoring. Communication is also desired to transmit intelligence from the surface to downhole t...

AI Technical Summary

Benefits of technology

[0028]In another aspect, the present disclosure describes a computer system having one or more input device, one or more output device, and one or more non-transitory computer readable medium storing instructions for (1) receiving a priori information of a particular, planned tubing for a borehole from the one or more input device, (2) predicting optimal carrier frequencies for acoustic communication utilizing the particular, planned tubing as a communication channel between two or more modems,

Problems solved by technology

One of the more difficult problems associated with any borehole is to communicate measured data between one or more locations down a borehole and the surface, or between downhole locations themselves.

Similarly when operating some of the downhole testing tools from surface, such as tester valves, circulating valves, packers, samplers or perforating charges, the operators do not obtain a direct feedback from the downhole tools.

However, it can be difficult to provide such communication using a cable since inside the tubing string it limits the flow diameter and requires complex structures to pass the cable from the inside to the outside of the tubing.

A cable inside the tubing is also an additional complexity in case of emergency disconnect for an offshore platform.

Space outside the tubing is limited and a cable can easily be damaged.

With respect to the non-uniform lengths, this is typically caused by the pipe sections being repaired by cutting part of the connection to re-machine the threads.

It will be appreciated that this method is time-consuming, requires installation and operation of the wireline probe and requires the services of a highly skilled operator.

This method, and the method which requires prior knowledge of a particular carrier frequency, are also not suited for coping with changes in the well environment over time (which will also change the optimum carrier frequency), without repeating the expensive and complex operation of calibrating or changing the carrier frequency.

However, the robustness of the system is not based solely on the carrier frequency.

When the received signals are decoded, the ISI causes bit errors.

If the bit rate is increased, the ISI increases and the probability of having bit errors also increase.

If the channel attenuates the modulated signals too much, the received signals cannot be properly decoded by the receiver.

In the downhole environment, it is difficult to increase the processing power of circuitry within the receiver due to the harshness of the downhole environment and limited power sources.

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