Development and evaluation of a coaxial cable sensing system for CO₂ sequestration wellbore integrity monitoring

Downhole monitoring plays a crucial part in geological carbon dioxide (2) sequestration. Various downhole monitoring technologies have been explored and applied, but they are either expensive or have system longevity issues. To address this issue, a robust and cost-effective downhole sensing system based on distributed coaxial cable sensors is developed and evaluated in laboratory, and a numerical simulation with staged finite element model is conducted to study the feasibility of using the coaxial cable sensing system for monitoring and evaluation of wellbore stability during CO2 injection. The real-time distributed sensing system is composed of Fabry-Perot interferometer based coaxial cable temperature and strain sensors. A high pressure high temperature (HPHT) sensor testing system is developed to study the temperature sensor accuracy, sensitivity, stability, hysteresis, and crosstalk effect under simulated downhole conditions. A lab-scale prototype of the casing imager based on strain sensors is developed and tested in laboratory to prove its real-time monitoring ability in casing axial compression, radial expansion, bending, and ovalization. A parametric study with staged finite element analysis is conducted to study the feasibility of using the casing imager in wellbore stability monitoring and evaluation during CO2 injection in the Weyburn field. The system is proved to perform under 1,000 psiaand 110 ⁰C, with real-time monitoring ability in casing axial compression, radial expansion, bending, and ovalization. And the parametric study with finite element model not only proved the feasibility of using the system for wellbore stability monitoring and evaluation during CO2 injection in the Weyburn field, but also provided insight into the best cementing practice and injection conditions as guidance to avoid leakage risks in a geologic CO2 sequestration project --Abstract, page i

Evaluation of ceramic coaxial cable sensors for long-term in-situ monitoring of geologic CO₂ injection and storage

Monitoring is an essential component of CO₂ injection and storage projects in order to manage the injection process, identify leakage risks, provide early failure warnings, determine the movement of CO₂ plume and provide input into reservoir models. In-situ monitoring provides critical and direct data points that can be used to fulfill the above objectives. However, downhole sensors that can withstand the harsh conditions and run over decades of the project life cycle remain unavailable. A new idea of ceramic coaxial cable temperature, pressure and strain sensor has recently been put forward and the sensors are under development. A high pressure high temperature (HPHT) testing system was developed in order to characterize the novel ceramic coaxial cable sensors under combined temperature, pressure and strain conditions with water, oil, brine, CO₂ and CO₂ brine mixture. Tests were conducted on a semi-rigid coaxial cable temperature sensor under combined temperature and pressure conditions with water. Besides, a preliminary test was conducted on the ceramic coaxial cable pressure sensor model to help with the design of the sensor. The semi-rigid coaxial cable temperature sensor showed an excellent ability of recording the actual temperature of hydraulic water with a constant resolution of ± 1 ºC. The preliminary test on ceramic coaxial cable pressure sensor model decided stainless steel as the proper material for sensor jacket. --Abstract, page iii