Drilling-induced hydrogen: A challenge for natural hydrogen exploration

In natural hydrogen exploration, recognizing artificial hydrogen generated by drill bit metamorphism (DBM) is crucial for correctly evaluating an area's natural hydrogen resource potential. This study presents cases where shallow drilling (<150 m vertical depth) with water in ultramafic and carbonate rocks generated high amounts of hydrogen and hydrocarbons. Using an integrated approach including mud gas analysis, water analysis, and soil gas surveys it can be shown that these gases can be attributed to reactions initiated during drilling. Whereas hydrogen is primarily generated by mechanochemical reactions or oxidation reactions, generation of hydrocarbons is related to secondary Fischer-Tropsch Type reactions and subordinate to thermal degradation of organic contaminations. The impact of DBM is significantly higher in ultramafic rocks compared to carbonate rocks, which can be attributed to the availability of Fe 2+ and silicate minerals as well as differences in drilling performance. • High H 2 concentrations detected during drilling of shallow boreholes with water. • H 2 is generated by drilling-induced mechanochemical and oxidation reactions. • Hydrocarbons can be attributed to Fischer-Tropsch Type reactions. • The impact of drill bit metamorphism on gas shows strongly depends on lithology. • Drill bit metamorphism needs to be considered in drilling-based H 2 exploration.