Operational overview of the first offshore production test of methane hydrates in the Eastern Nankai Trough

TLDR

The first worldwide field trial of gas production from marine methane hydrate deposits was conducted in March 2013 at the Daini Atsumi Knoll in the Eastern Nankai Trough. The study aims to evaluate the feasibility of the depressurization technique for methane hydrate extraction. A single production well with two monitoring boreholes was drilled, and a depressurization flow test was run from March 12 until sand production forced termination after six days, while extensive temperature, pressure, and physical‑property data were collected. During the stable phase, the well produced roughly 20 000 m³ of gas per day with a gas‑liquid ratio exceeding 100, and a large dataset of formation conditions was obtained.

Abstract

Abstract In March 2013, the world's first field trial of gas production from marine methane hydrate deposits was conducted in the Daini Atsumi Knoll area of the Eastern Nankai Trough off the Pacific coast of Japan as a process to bring gas hydrates under seafloor to valuable energy resource. The technique used to dissociate the ice-like material was "depressurization method" that had been applied in the previous production test in Mallik site, the Northwest Territories, Canada in 2007-2008. Japan Oil, Gas and Metals National Corporation (JOGMEC) as a part of MH21, the Research Consortium for Methane Hydrate Resources in Japan planed and supervised the project with the funding of the Ministry of Economy, Trade and Industry (METI), and scientific supports from the National Institute of Advance Industrial Science and Technology (AIST). One production well with two monitoring boreholes were drilled in the test site for the test. Along with the flow test operation, intensive data acquisition program was planned and implemented to understand behavior of methane hydrate dissociation- bearing sediments against depressurization. To realize high degree of drawdown in relatively shallow formation below deepwater, several downhole devices were designed and installed. The flow test started in the morning of March 12 and lasted until severe sand production forced to terminate the operation six days later. During the stable production term, gas flow rate was approximately 20,000m3 under atmospheric condition, and gas liquid ratio was larger than 100. A lot of data including formation temperatures, fluid pressure and temperature, and physical property changes in the formation were obtained. The data taken are under studies to verify applicability of the depressurization technique as a methane hydrate production technologies.