A Chemical CO2 Sensor Monitoring CO2 Movement Under Reservoir Conditions

A down-hole CO₂ sensor may continuously collect real-time data about CO₂ movement and concentration change at subsurface condition. These data are very valuable for the better understanding of subsurface uncertainties and quality-controlling theoretical studies such as reaction, transport, and mechanics in shallow offshore depleted oil and gas fields. In this paper, a downhole CO₂ sensor was developed and the sensor was tested under high pressure and reservoir conditions to monitor CO₂ concentration change. The developed CO₂ sensor is a Severinghaus-type sensor, which includes a metal-oxide electrode, a gas-permeable membrane, a porous steel cup, and a bicarbonate-based internal electrolyte solution. The CO₂ sensor, after prepared, has the size of diameter of 0.7 in. and length of 1.5 in. A linear correlation was observed between the sensor output potential change and dissolved CO₂ in water under the pressure of 2,000 psi. CO₂/brine coreflooding tests were performed to simulate the CO₂ storage process and the prepared CO₂ sensor was deployed to monitor the CO₂ movement. The results indicated that the CO₂ sensor could in-situ monitor CO₂ movement in CO₂ storage process.