Geologic Controls on the Genesis of the Arctic Permafrost and Sub-Permafrost Methane Hydrate-bearing System in the Beaufort–Mackenzie Delta

The Canadian Mackenzie Delta (MD) is a river-mouth depocentre and the second-largest Arctic delta. It exhibits high resources of prospected sub-permafrost gas hydrates (GHs), mainly consisting of thermogenic methane (CH₄) at the Mallik site, which migrated from deep source rocks. The objective of the present study is to confirm the sub-permafrost GHs formation mechanism proposed by Li et al. (2022a), stating that CH₄-rich fluids were vertically transported from deep overpressurized zones via geologic fault systems and formed the present-day GH deposits in the shallower Kugmallit Sequence since the Late Pleistocene. Given this hypothesis, the coastal permafrost began to form since the early Pleistocene sea-level retreat, steadily increasing in thickness until 1 Million years (Ma) ago. Observations from well-logs and seismic profiles were used to establish the first field-scale static geologic 3D model of the Mallik site. A framework of equations of state to simulate the formation of GHs and permafrost (Li et al., 2022a, 2022b) has been developed and coupled with a numerical simulator for fluid flow as well as the transport of chemical species and heat in previous studies. Here, numerical simulations using the proven thermo-hydro-chemical simulation framework were employed to provide insights into the hydrogeologic role of the regional fault systems in view of the CH₄-rich fluid migration and the spatial extent of sub-permafrost GH accumulations during the past 1 Ma. The simulated ice-bearing permafrost and GH interval thicknesses, as well as sub-permafrost temperature profiles, are consistent with the respective field observations, confirming our previously introduced hypothesis. In addition, simulation results demonstrate that the permafrost has been substantially heated to 0.8–1.3 °C, triggered by the global temperature increase of about 0.44 °C (IPCC, 2022) and further accelerated by Arctic amplification from the early 1970s to the mid-2000s. Overall, the good agreement between simulations and observations demonstrates that the present modeling study provides a valid representation of the geologic controls driving the complex permafrost-GH deposit system. The model’s applicability for predicting GH deposits in permafrost settings can provide relevant contributions to future GH exploration and exploitation activities.

References

IPCC, 2022: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. Cambridge University Press, Cambridge, UK and New York, NY, USA, 3056 pp., doi:10.1017/9781009325844.

Li, Z., Spangenberg, E., Schicks, J. M. & Kempka, T. Numerical Simulation of Coastal Sub-Permafrost Gas Hydrate Formation in the Mackenzie Delta, Canadian Arctic. Energies 15, 4986 (2022a). https://doi.org/10.3390/en15144986

Li, Z., Spangenberg, E., Schicks, J. M. & Kempka, T. Numerical Simulation of Hydrate Formation in the LArge-Scale Reservoir Simulator (LARS). Energies 15, 1974 (2022b). https://doi.org/10.3390/en15061974