Possible inflow of fluid at the seafloor following gas production from methane hydrates: Numerical simulation studies.

Abstract

The Hikurangi Margin east of New Zealand, is reported to contain methane hydrate deposits in abundance. Methane hydrates are predicted to cover over 50,000 km2 of the margin with New Zealand’s conventional gas supplies being rapidly depleted, methane hydrates on the margin have attracted a lot of attention as a possible unconventional energy source. Furthermore, they are being studied because of their possible role in submarine slope stability, climate change, and ocean acidification. The Margin is geographically located where the Pacific Plate subducts under the New Zealand’s continental crust. It is characterised by anticlinal ridges that are adjacent to a Mesozoic basement composed of Torlesse terrane greywackes. This compressional deformation consists of three major heterogeneous sedimentary rocks. These rocks are Late Cretaceous and Paleogene rocks, late Cenozoic trench-fill turbidites, and a sequence of Miocene to Recent shelf and slope basin sediments which also may act as a traps for gas hydrate accumulation. In our studies, we used TOUGH+HYDRATE to construct a 2-D cylindrical axisymmetric gas production model of the margin using measurements from geophysical and geochemical surveys. The focus of our studies is the significance of the overburden to gas production, in particular simulating both permeable and impermeable overburden. Our studies are conceptual but we are basing our models on seismic images from an anticline, Uruti Ridge, at 725 m water depth as well as a site close to the up-dip edge of gas hydrate stability. We will present results for various basic scenarios varying in particular permeability of the overburden. We found that for higher permeability, sea water is being sucked into the reservoir for models with permeable overburden. Such a reversal of fluid flow near the seafloor would have significant implications on for seafloor biologic communities, which constitute a major challenge for possible gas hydrate production.

AAPG Datapages/Search and Discovery Article #90348 © 2019 AAPG Asia Pacific Region Geosciences Technology Workshop, Gas Hydrates – From Potential Geohazard to Carbon-Efficient Fuel?, Auckland, New Zealand, April 15-17, 2019