Surveillance and Monitoring for Hydrogen Storage

Objective: It is important to have surveillance and monitoring methods capable of evaluating and managing operational risks of GHS and to assure the protection of overlying aquifers. Safe handling of hydrogen and flammable gases is regulated by Occupational Safety and Health Administration (OSHA) and codes such as National Fire Protection Association (NFPA) 2 and International Fire Code (IFC).

Hydrogen safety sensors

Sensors Temporal Spatial TRL
Catalytic Pellistors Real-time Point sensor 9
Electrochemical Sensors Real-time Point sensor 9
Thermal conductivity sensors Real-time Point sensor 9
Resistive sensors Real-time Point sensor 9
Work function sensors Real-time Point sensor 6-9
Optical schlieren imaging. Shadowgraph Real-time Standoff sensor 6-8
Raman Lidar Real-time Standoff sensor 6-8
Acoustic leak detection Real-time Standoff sensor 9
Optrode Real-time Point Sensor 6-8
Distributed Optical Fiber Sensors Real-time Distributed sensor 5-8
Passive wireless SAW sensors Real-time Point sensors 5-6

Surface-based geophysical methods and downhole monitoring tools

Tools Tool Location Measurements Information
Magnetotellurics (MT) Electromagnetic (EM) geophysical method at the surface Subsurface electrical conductivity Tracking gas-plume migration
Electrical resistivity tomography (ERT) Electrical method at the surface Electrical resistivity Tracking gas-plume migration
Gravity survey At the surface Mass-based gravity Tracking gas-plume migration
Seismic reflection Surface seismic survey Reflected seismic waves Tracking gas-plume migration
Downhole pressure monitoring Downhole Pressure Early detection of gas-leakage plumes in overlying aquifers
Downhole total dissolved solids (TDS) monitoring Downhole Downhole TDS Gas-leakage detection in overlying aquifers may be of limited value due to low solubility of H2 and CH4

Conclusions: Sensors and wellbore monitoring tools can be leveraged from the H2-handling industry, geological CO2 sequestration community, oil and gas industry, with experience from the UGS industry being most relevant. There is a need to develop cost-effective approaches for monitoring over broad areas due to the greater mobility and buoyancy of H2/CH4 gas plumes, compared to pure CH4 plumes.

As H2 and CH4 are both flammable gases, it is important to have surveillance and monitoring to evaluate and mange operational risks of UHS. Therefore, real-time monitoring is needed to assure storage infrastructure integrity and to detect early signs of gas leakage. Safe handling of hydrogen and flammable gases is regulated by Occupational Safety and Health Administration (OSHA) and codes such as National Fire Protection Association (NFPA) and International Fire Code (IFC).

As hydrogen has been used by industry for a long time, there are many commercial hydrogen sensors including catalytic combustion sensors, electrochemical sensors, thermo-conductivity sensors, resistive sensors, acoustic leak sensors, and optical based sensors. Existing sensor technologies are mostly point or standoff hydrogen sensors, but there is a need for wide-area and long-distance monitoring for hydrogen leak detection in large-scale UHS facilities. Moreover, subsurface conditions are more challenging, due to higher pressures and temperatures than encountered in typical sensor-operating conditions. Emerging sensor technologies such as optical fiber sensors and passive wireless sensors are inert and free of electrical wire, which are safer in flammable H2/CH4 gas mixture compared to electrical-based sensors.

Wellbore surveillance technologies used for CO2 storage wells and oil and gas wells can be leveraged and translated to subsurface H2/CH4 storage wells. Monitoring of groundwater quality to identify geochemical changes may be required to prevent groundwater contamination due to UHS. Commonly used surface-based geophysical methods include bulk electrical resistivity methods such as magnetotellurics and electrical resistance tomography, gravity survey, and seismic reflection, and they can provide information based on physical parameters of rock, fluid, and gas in the subsurface (e.g. electrical resistivity, mass density) in a large volume and construct 3D subsurface images. Downhole monitoring methods of pressure and total dissolved solids (TDS) are sensitive to H2/CH4 gas and TDS and can improve detection of gas migration and add confidence of leak detection when combined with surface-based geophysical methods. Experience with induced seismic events at UGS facilities is very limited. There is significant experience in seismic monitoring and risk management in the oil and natural gas, wastewater disposal, and CO2 sequestration domain that can be applied to seismically problematic gas storage operations.