Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

Abstract

Methane hydrate concentrated zones (MHCZs) have become targets for energy exploration along continental margins worldwide. In 2013, exploratory drilling in the eastern Nankai Trough at Daini Atsumi Knoll confirmed that MHCZs tens of meters thick occur directly above bottom simulating reflections imaged in seismic data. This study uses 3-dimensional (3D) seismic and borehole data collected from the Kumano Basin offshore Japan to identify analogous MHCZs. Our survey region is located ~100 km southwest of the Daini Atsumi Knoll, site of the first offshore gas hydrate production trial. Here we provide a detailed analysis of the gas hydrate system within our survey area of the Kumano forearc including: (1) the 3D spatial distribution of bottom simulating reflections; (2) a thickness map of potential MHCZs; and (3) a volumetric gas-in-place estimate for these MHCZs using constraints from our seismic interpretations as well as previously collected borehole data. There is evidence for two distinct zones of concentrated gas hydrate 10–90 m thick, and we estimate that the amount of gas-in-place potentially locked up in these MHCZs is 1.9–46.3 trillion cubic feet with a preferred estimate of 15.8 trillion cubic feet.

Keywords

• gas hydrates
• Kumano Basin
• bottom simulating reflections
• methane hydrate exploration
• 3D seismic interpretation
• Nankai Trough