Wireless System for Long-term and Real-time Subsurface CO2 Monitoring
The data and power transfer systems for long-term underground CO2 sequestrationmonitoring are normally based on wire-line cable, which will lead to a high potentialleakage path through casing and cement annulus in high-temperature, high-pressure, andhash underground environments. In this dissertation, a novel wireless communication andpower transfer system has been developed for real-time underground CO2 monitoring. Thesystem includes an array of toroidal transceivers winding around the highly conductivecasing string for wireless power transfer to the deep subsurface, which helps to maintainwell integrity and reduce potential leakage by eliminating the need to perforate the casingor an umbilical in the cement annulus. The metal casing’s amplification effect significantlyenhances the wireless power transfer efficiency and communication performance, whichprovides a highly conductive power/electric current pathway instead of omnidirectionalwireless radiation loss in the subsurface. The toroidal transceiver’s design has beenoptimized to improve the received signal, and our results show significant improvementsin wireless power transfer efficiency. Using the optimized design, we can receive 1 to 10 %power transfer efficiency at 800 meters deep using only one toroidal transceiver with 1Acurrent as input. Compared with other wireless antenna designs, such as the helix coilantenna, our system has shown 26,000 times power transfer efficiency improvement. Usingthe optimized design, for this 800 m long subsurface wireless system, the channel capacitycould improve about 14,000 times from 0.35 bps to 5 kbps, and the energy efficiencyimproved 109times from 10-3bit/J to 106bit/J. For experiments, a lab-scale system is built,and our experimental receiving voltage measurements support the simulation results. Thisscaled-down wireless communication system with USRP as transceivers was tested atvidifferent symbol rates and the bandwidth from the voltage signal spectrum andconstellation figures were compared and matched.Furthermore, we tried to use this system not only for leakage monitoringcommunication but also for CO2 migration monitoring. We tested the model with andwithout the CO2 plume, we could see the difference response from the voltage signal. Atthe same time, we build a new model in COMSOL to do the time-domain reflectometry(TDR), the difference of properties can also be detected.