A Chemical CO2 Sensor Monitoring CO2 Movement Under Reservoir Conditions

Abstract

A dowhole CO 2 sensor can continuously collect real-time data about CO 2 movement and concentration changes at subsurface conditions. These data are very valuable for better understanding of subsurface uncertainties and quality-controlling theoretical studies such as reaction, transport, and mechanics in oil and gas formations. This paper describes the development of a downhole CO 2 sensor tested under high pressure and reservoir conditions to monitor aqueous CO 2 concentration change. The CO 2 sensor developed 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 CO 2 sensor thus prepared 0.7 in. in diameter and 1.5 in long. A linear correlation was observed between a change in sensor output potential and dissolved CO 2 in water under 1,000 psi pressure. CO 2 /brine coreflooding tests were performed to simulate the CO 2 storage process and the sensor was deployed to monitor CO 2 movement. The results indicated that the CO 2 sensor could monitor CO 2 movement in-situ in CO 2 storage processes.