Site Selection and Formation Evaluation at the 1st Offshore Methane Hydrate Production Test Site In the Eastern Nankai Trough, Japan

In order to evaluate productivity of gas from marine gas hydrate by the depressurization method, Japan Oil, Gas and Metals National Corporation is planning to conduct a full-scale production test in early 2013 at the AT1 site in the north slope of Daini-Atsumi Knoll in the eastern Nankai Trough, Japan. By the pre-drilling campaign conduced in early 2012, we confirmed methane hydrate concentrated zone (MHCZ) with 60 m of gross thickness, which is composed of lobe/sheet type sequences in the upper part of it and channel type sand sequences in the lower part. This MHCZ is thicker than that of confirmed at previous wells in 2004 (45 m) located around 150 m northeast, indicating that the prediction provided by seismic interpretation and inversion analysis was reasonable. Well-to-well correlation between two monitoring wells (AT1-MC and MT1) within 40 m distance exhibited that lateral continuity of these sand layers (upper part of reservoir) are fairly good, which representing ideal reservoir for the production test. The XPT fluid mobility measurement results showed approximately 0.1 to several mD of water permeability in both MHCZ and seal formation, although there are some variations in measured values.