Methane Hydrate Stability and Potential Resource in the Levant Basin, Southeastern Mediterranean Sea

摘要

To estimate the potential inventory of natural gas hydrates (NGH) in the Levant Basin, southeastern Mediterranean Sea, we correlated the gas hydrate stability zone (GHSZ), modeled with local thermodynamic parameters, with seismic indicators of gas. A compilation of the oceanographic measurements defines the 1 km deep water temperature and salinity to 13.8 °C and 38.8‰ respectively, predicting the top GHSZ at a water depth of ~1250 m. Assuming sub-seafloor hydrostatic pore-pressure, water-body salinity, and geothermal gradients ranging between 20 to 28.5 °C/km, yields a useful first-order GHSZ approximation. Our model predicts that the entire northwestern half of the Levant seafloor lies within the GHSZ, with a median sub-seafloor thickness of ~150 m. High amplitude seismic reflectivity (HASR), correlates with the active seafloor gas seepage and is distributed across the deep-sea fan of the Nile within the Levant Basin. Trends observed in the distribution of the HASR are suggested to represent: (1) Shallow gas and possibly hydrates within buried channel-lobe systems 25 to 100 mbsf; and (2) a regionally discontinuous bottom simulating reflection (BSR) broadly matching the modeled base of GHSZ. We therefore estimate the potential methane hydrates resources within the Levant Basin at ~100 trillion cubic feet (Tcf) and its carbon content at ~1.5 gigatonnes.