Laboratory evaluation of distributed coaxial cable temperature sensors for application in CO 2 sequestration well characterization

Downhole monitoring plays a crucial part in a geological carbon dioxide (CO 2 ) sequestration project, especially in providing early warnings of failure. However, most downhole monitoring technologies are often low in spatial resolution and time‐consuming, or expensive and have system longevity issues. To address this issue, a robust and cost‐effective distributed coaxial cable Fabry‐Perot interferometer‐based temperature sensor is proposed for real‐time downhole monitoring. The coaxial cable sensor (CCS) was made in house and tested using a high pressure high temperature (HPHT) testing apparatus to study the sensor accuracy, sensitivity, stability, and crosstalk effect in simulated downhole conditions. The laboratory test results indicate that the sensor can work under simulated downhole conditions of pressures up to 1000 psia and temperatures up to 110°C. At 1 ATM, the sensor has an accuracy of about 1%. At 1000 psia, the hysteresis phenomenon is observed, but it is reduced and tends to stabilize after repeated heating and cooling treatments. The pressure crosstalk effect was observed on the flexible cable sensor and minimized on the rigid cable sensor. The temperature and pressure range of the distributed CCS allows long‐term in situ monitoring for a well depth up to 2500 feet, which would prove of great value in detecting temperature change associated with wellbore leakage that may lead to groundwater contamination. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd