Hydrogen Discovery in Abu Dhabi, UAE? A Geochemical Journey to Decipher the Source of 60 Mole% Hydrogen and in an Annulus-B of an Oil Producer Well

Abstract Hydrogen, the lightest and most prevalent element in the cosmos, has attracted notable interest as a possible resource beneath the Earth's surface. Being a pervasive and vital component of the earth's crust, making up about 0.5% of the earth's mass, hydrogen is integral to a variety of geological activities like hydrothermal events, diagenesis, and metamorphism. Its existence in geological structures, especially within the circular spaces of wells, raises compelling debates regarding its origins, pathways, and concentrations. Investigating subsurface hydrogen necessitates an interdisciplinary strategy that entails geochemical examinations, geophysical explorations, and geological projections to demystify its movements and reactions. Prospective origins of endogenic hydrogen may include biological activity, interactions between water and rocks, volcanic activity, sedimentary environments, and the microbial breakdown of organic compounds, with each source imparting distinct geochemical traces. The exploration of hydrogen in the subsurface involves a multidisciplinary approach, combining geochemical analysis, geophysical surveying, and geological modeling to unravel the complexities of its behavior. Its presence within geological formations, particularly in the annular spaces of wells, poses intriguing questions as well as necessitates proper understanding to mitigate any potential danger or contamination risks associated with its migration and potential impact on drilling operations and well integrity. 60 mole% "Hydrogen", 39.7 mole% "Nitrogen" and "Methane" in traceable amounts has been observed in an annulus-B of a well in Abu Dhabi, UAE. Comprehensive geochemical characterization that included isotope and noble gas analysis was performed on produced gas, annular space gas and produced water samples collected from the well with the objective to determine the origin of high concentrations of hydrogen and nitrogen accumulating in the annular space. Geochemical analysis results indicate that radiolysis in basement rocks might seem a plausible source of the hydrogen in the annulus-B gas because both the hydrogen and nitrogen isotope data are consistent with a crustal source. However, this is a very speculative idea because the hydrogen generation process in basement rocks is very slow and the H2 would require a highly efficient and direct migration fairway directly to the annulus-B space. Hydrogen is not found in the reservoir gases produced from the well or in any of the other wells producing in the field. Furthermore, the noble gas results demonstrate that migration from deeper basement sources did not occur while significant degassing from water did. The data suggest that hydrogen generation in the Annulus-B space is operational and related to a problem with the cathode protection system in the well. Cathodic protection systems are considered to be the principal source of hydrogen in the annuli of water and oil/gas wells. Also, the high nitrogen concentration (39.7 mole%) in the annulus-B gas is problematic. Two possible sources for this N2, based on the N isotope value of +10.1‰, are denitrification and ammonium released from clays by brine interaction. Brown (2019) considers the latter as the only significant source for gases with nitrogen heavier than 7‰, but then he does report denitrification N2 with ẟ15N values in the 3 to 30‰ range. A denitrification source would implicate microbial processes and the N2 would be associated with microbial CH4. There is only a trace of methane in this gas (0.055 mole%) along with wisps of C2+. The 3He/4He ratio (R/Ra = 0.0354) clearly indicates crustal gas. An ammonium source is the most likely interpretation. It is independent of thermal maturity and the process is active where brine interacts with clays containing ammonium. Nitrogen is a common and often major component of evaporite deposit gases (Warren, 2016). The annulus-B nitrogen might be associated with Rus Formation evaporites or any other evaporites that exist in that area. In light of the results, we conclude by recommending that future research prioritize the evaluation of the wells cathode protection system integrity, as well as a comprehensive analysis of the produced gases to identify potential microbial activity, thermal maturity of hydrocarbons, and relationships between methane, hydrogen, and produced water. A thorough gas geochemistry study of the producing wells in the field should also be conducted to establish a baseline for fugitive nitrogen and hydrogen investigations. Additionally, collecting annulus-B water samples and analyzing the carbon isotope ratio of dissolved methane could provide valuable insights. Finally, a detailed evaluation of geological and geophysical data is necessary to constrain plausible sources and migration pathways of N2 and H2