Evaluation of Sensitivity of Downhole Temperature Estimates From Distributed Temperature Sensing Measurements

Abstract

A range of Australian CCS research activities (CO2CRC Otway Stage 3, CO2CRC Otway shallow controlled release and CSIRO Insitu-lab) involving subsurface characterisation and/or CO2 injection are at the planning stage. Fibre-optic sensing is considered as part of the downhole reservoir characterisation and surveillance monitoring system for all of these projects. In this work, we investigate the sensitivity of DTS for the detection of thermal anomalies in view of the design of future geological storage activities in Australia. Ahead of Phase 2 of the CO2CRC Otway shallow CO2 controlled release experiment, a DTS system was installed in the CRC-3 well for equipment testing and baseline characterisation, at the same time as the acquisition of the CO2CRC Stage 2C M5 seismic survey. Temperature measurements were acquired from well-head to bottom-hole for 13 days at a rate of one-minute measurement every 4 minutes. The temperature profile did not change significantly over time. The integration and processing of more than 3400 temperature traces enabled estimation of a temperature profile with a resolution of 0.01 °C. The use of DTS during the CO2CRC M5 survey highlights the detectability of a VSP tool producing 11W and 4W at two distinct depths. The setup was capable of detecting a 0.7 °C anomaly very quickly. A smaller anomaly (0.1 °C) was detected with the benefit of data processing of the long term dataset. The high spatial resolution of DTS enables location of thermal anomalies to within 2 metres.