Publications Details

High Temperature High Speed Downhole Data Transfer (Data Link)

Wright, Andrew A.; Cashion, Avery T.; Tiong, Francis

In high temperature (HT) environments often encountered in geothermal wells, data rate transfers for downhole instrumentation are relatively limited due to transmission line bandwidth and insertion loss and the processing speed of HT microcontrollers. In previous research, Sandia National Laboratory Geothermal Department obtained 3.8 Mbps data rates over 1524 m (5000 ft) for single conductor wireline cable with less than a 1x10-8 bit error rate utilizing low temperature NITM hardware (formerly National InstrumentsTM). Our protocol technique was a combination of orthogonal frequency-division multiplexing and quadrature amplitude modulation across the bandwidth of the single conductor wireline. This showed it is possible to obtain high data rates in low bandwidth wirelines. This paper focuses on commercial HT microcontrollers (µC), rather than low temperature NITM modules, to enable high-speed communication in an HT environment. As part of this effort, four devices were evaluated, and an optimal device (SM320F28335-HT) was selected for its high clock rates, floating-point unit, and on-board analog-to-digital converter. A printed circuit board was assembled with the HT µC, an HT resistor digital-to-analog converter, and an HT line driver. The board was tested at the microcontroller's rated maximum temperature (210°C) for a week while transmitting through a 1524 m (5000 ft) wireline. A final test was conducted to the point of failure at elevated temperatures. This paper will discuss communication methods, achieved data rates, and hardware selection. This effort contributes to the enhancement of HT instrumentation by enabling greater sensor counts and improving data accuracy and transfer rates.