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

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.

Numerical simulations for analyzing deformation characteristics of hydrate-bearing sediments during depressurization

“…Among the methods mentioned above, the depressurization method is the most economical and effective one (Lee et al, 2011;Konno et al, 2016). As a consequence, the depressurization method has been adopted in field productions of NGHs in the Messoyakha gas field (Krason, 2000), the North Slope of Alaska (Schoderbek et al, 2013), the Nankai Trough in Japan Sea (Cyranoski, 2013;Yamamoto et al, 2014), and the Shenhu Area in South China Sea. Solid NGHs are decomposed into liquid water and natural gas during depressurization.…”

Multiphase Flow Behavior of Layered Methane Hydrate Reservoir Induced by Gas Production

“…Figure 7 shows the depressurization processes both in field test and in this simulation, which lasted for about 6 days. As shown in Figure 7, the wellbore pressure of production well was decreased from approximately 13 MPa to about 4 MPa during the first day and then remained almost stable for 5 days [29]. In the morning of the 6th day, sudden water rate increase was observed followed by strong sand production to the surface, and then the flow test was terminated [29].…”

“…MHCZ was characterized as sand-dominant methane hydrate with high saturation [4]. The AT1 site within the -MHCZ, located in the north slope of Daini Atsumi Knoll area, is the 2013 production test site [22,29]. The area of -MHCZ is about 12 km 2 with the water depth ranging from 857 to 1405 m [22,28].…”

“…In 2012, the production well (AT1-P), two monitoring wells (AT1-MC and AT1-MT1), and sampling well (AT1-C) were drilled at the AT1 site [22,29]. The well locations and their trajectories projected in the horizontal section are shown in Figure 1.…”

“…The model size in R-direction is 1000 m to avoid the boundary effects. The total thickness of the entire model is 100 m with the thickness of MHCZ being 61 m. The production well with a radius of 0.1 m is located in the center of the cylinder [29,32]. Production interval was 38 m from the top of the MHCZ for expecting the lower part of MHCZ as sealing layer to prevent water production [22].…”