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Abstract The emerging natural H2 (white hydrogen or naturally occurring geological hydrogen) exploration requires adjustments in current petroleum-oriented drilling and logging practices. This paper presents the results of wellsite and laboratory experiments on H2 logging while drilling using different degassing and gas analysis techniques, including direct mass spectrometry while drilling and laboratory gas chromatography-thermal conductivity detector analysis. Additional proposed developments concerning dedicated natural H2 logging analyzers are described, e.g., cavity-enhanced Raman spectroscopy. Furthermore, the challenge of artificially generated H2 while drilling using oil-based mud can be mitigated using alkene or carbon monoxide data either from logging or spot samples. Ultimately, a methodology targeting quantitative natural H2 logging is proposed for prospecting and documenting this new resource in drilling for oil and gas and geothermal or in dedicated H2-exploration wells.
Introduction Due to the changing global climate, the role of renewable and non-fossil carbon energy sources is of increasing importance. H2 can play an important role as an energy carrier in the energy transition. However, a highly reliable and sensitive hydrogen sensor is required during exploration, production, and transportation of natural H2, i.e., for concentration quantification and leakage monitoring. The main incentive for the proposed workflow being presented is to create and provide a service that quantifies naturally occurring H2 as one of the energy sources and currencies of the near future with helium as a high-value collateral in any type of drilling operation. These operations include direct exploration for H2, e.g., in Mali, hybrid exploration with petroleum drilling, e.g., in Australia, or with geothermal exploration, e.g., in Djibouti. Such a workflow and comprehensive methodology dedicated to natural H2 does not exist and can provide a leading-edge window in opening this clean energy opportunity.
H2 can exist naturally at high concentrations, even >90%, in locations such as Bourakebougou, Mali, or associated with natural gas to several percent in the Canning Basin, Australia. Other examples of encountering H2 include geothermal wells in Djibouti or Iceland rift zones, and intracratonic locations such as Kansas, USA or Russia. Often, H2 generation is associated with water interacting with ultrabasic rocks (e.g., serpentinization of olivine-rich ophiolites), such as in the Chimaera eternal flame, Turkey, or in the cool alkaline hydrothermal vents (e.g., Lost City) and hot acidic black smokers at the mid-Atlantic ridge. Such environments are typically different or distant from petroleum exploration areas in sedimentary basins. Thus, potentially huge natural H2 volumes remain untapped while commercial production is still limited, i.e., Kansas, Mali, and planned soon in Russia (Siberia and Sakhalin). Additional evaluations are ongoing in Djibouti and Australia. H2 exploration can be combined with ongoing petroleum and geothermal drilling campaigns, e.g., in fractured basement. Despite being very leak prone, H2 might occasionally accumulate in conventional reservoirs, e.g., in Mali. However, geothermal wells are a more natural environment to encounter H2 because these wells are frequently drilled in crystalline rocks of tectonically active zones, which often involve hydrothermal activity. All of these factors are potential H2 sources or conduits of lower crust or upper mantle H2, whereas in shallower zones, mafic rocks generate H2 when exposed to water. H2 logging in any well can add value or be used for documentation of future resources, which requires proper quantification of H2. The major challenge is H2 insolubility in drilling fluids. As a result, to avoid immediate degassing on the surface before the H2 reaches an analyzer, an in-mud-loop degasser or sensor suspended within the mud flow should be used. H2 often exists in and is transported preferably by small-scale features such as faults, fractures or joints, e.g., in crystalline rocks, which require high-frequency sensors to deliver high-depth resolution data.
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