Yashee Mathur1, Tapan Mukerji1
1Department of Energy Science and Engineering, Stanford University, Stanford CA
Hydrogen’s role is undebatable in the future energy mix owing to its energy density, use in different industries, long-term energy storage capabilities, and minimal CO2 production. The Earth hosts vast resources of naturally occurring hydrogen in different geological environments but the exploration for natural hydrogen is still in the very early stages. Abiogenic sources such as serpentinization and radiolysis are considered the main secondary sources of natural hydrogen generation. Rock physics and geophysical methods have been used over decades to characterize hydrocarbon reservoirs, minerals, and groundwater resources which has in turn led to a better understanding of these resources and a more efficient exploration. Can we adapt and develop characterization workflows that link geophysical signatures to the rock properties of subsurface natural hydrogen reservoirs?
For example, the physical properties of the rocks change during the formation of natural hydrogen by serpentinization. Highly serpentinized peridotites have very low densities and increased volume in relation to their protoliths and may have very high magnetic susceptibilities compared with their protolith also leading to magnetic and gravity anomalies. Moreover, the hydrogen-emitting sub-circular depressions have been shown to be aligned with the dominant geomorphological features or fault trends that can be easily mapped using different types of geophysical data. In the current work, we outline and discuss all the different types of geophysical and rock physics techniques that can aid in the efficient exploration of natural hydrogen and show case studies where available.
Major geophysical techniques amenable for hydrogen exploration can be further divided into two broad categories as follows:
1. Surface techniques:
a. Geochemical soil gas sampling (includes a brief case study of geochemical soil gas sampling near the San Andreas Fault (Mathur et al. 2023))
b. Remote sensing with machine learning for mapping fairy circles (brief case study from Carolina Bays)
c. Gravity and magnetic surveys to identify density and magnetic anomalies.
d. Muon tomography- a low-cost way to create a 3D map of density variations in the subsurface
2. Sub-surface techniques:
a. Analysis of well-log measurements and
b. Rock physics modeling for reservoir and fluid characterization with a case study from Hoarty NE-3 well drilled in Nebraska, USA
c. Seismic data acquisition and its usefulness for hydrogen reservoirs
With the exploration of natural hydrogen quickly ramping up, it is prudent and timely to identify and develop geophysical and other remote sensing methods that can explore and characterize hydrogen reservoirs specifically. The talk aims to discuss how these techniques can be adapted for hydrogen reservoir characterization as well as the merits of each of the techniques.
Mathur Y et al., Soil geochemistry of hydrogen and other gases along the San Andreas fault, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2023.09.032