Limits on Data Communication Along the Drillstring Using Acoustic Waves

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe first commercial acoustic telemetry system was successfully introduced in 2000 as part of a drillstem testing system. However, duplicating the success of the acoustic telemetry to environmentally challenging LWD applications at high data throughput remains a formidable task. The primary limitation arises from normal drilling operations that produce in-band acoustic noise at multiple sources at intensities comparable to the transmitter output. This noise, together with the signal attenuation along the drill string, adversely affects the data throughput. To determine the communication capacity of the drill string channel using acoustic waves, we examined the impact of channel characteristics, signal attenuation and noise in detail. Based on a communication model which incorporates the effects of both drill string acoustic channel and noise, we extensively studied the capacity of the system using the waterfilling method. For this analysis, realistic downhole transmitter power output, experimentally measured noise at the surface, and measured attenuation of acoustic waves in the drill string were used as input parameters. The results show that a typical drill string channel has a potential capacity of up to several hundred bits per second under noisy drilling conditions. Implications of the channel capacity on acoustic telemetry system designs are discussed.A communication technique that comes close to realizing a highrate telemetry system is introduced. Methods to optimize various aspects of the system such that maximum channel utilization can be realized under drilling conditions are also discussed. Potential enhancement to data rates through application of error control coding is briefly covered.

Signal Transmission Capability Improvement of a Telemetry Drill String Using the Reflected Signal at the Transmission Line Termination

“…e downhole information assists drilling engineers operate the rig correctly and drive the bit drill into oil and gas reservoir formations along corresponding tracks in order to drill quickly [4,5], safely [6][7][8], and efficiently [9]. e downhole data transmission rates using wireless transmission technologies, including the mud pressure pulse [10,11], the formation electromagnetic wave [12,13], and the drill string sound wave [14][15][16], are very low (dozens of bit/s). In 2003, Grant Prideco developed the IntelliServ network system [17], a downhole data wired transmission system, using a drill pipe to transmit high-frequency electromagnetic signals, and its data transmission rate can reach 2 Mbit/s at a 2 MHz channel bandwidth (using quadrature phase-shift keying modulation or QPSK modulation).…”

A New Type of Electroacoustic Transducer Used for Downhole Acoustic Telemetry System

“…Last, the real-time parameters of the downhole could be got. Research results show that high-power low-frequency electroacoustic transducer design is one of the key techniques for downhole ATS [3]. But the conventional piezoelectric transducer is very difficult to meet the requirements, so it is necessary to study a new type of electroacoustic transducer with the giant magnetostrictive material [4,5].…”