Application of a Simulation Model for the Formation of Methane Hydrate to the Nankai Trough and the Blake Ridge: Natural Examples of Two End‐member Cases

Abstract

Abstract:Simulation experiments with a one-dimensional static model for formation of methane hydrate are used to demonstrate models of hydrate occurrence and its generation mechanism for two end-member cases. The simulation results compare well with experimental data for two natural examples (the Nankai Trough and the Blake Ridge).At the MITI Nankai Trough wells, the hydrate occurrence is characterized by strongly hydrated sediments developing just above the BGHS. Such occurrence can be reproduced well by simulation in which the end-member case of upward advective fluid flow from below the BGHS is set. The strongly hydrated sediments is formed by oversaturated solution with free gas which directly enters the BGHS by the upward advective fluid flow. The recycling of dissociated methane of preexisting hydrate also contributes to the increase of hydrate saturation.At the Site 997 in the Blake Ridge area, the hydrate occurrence is characterized by thick zone with poorly hydrated sediments and no hydrate zone developing above the hydrate zone. Such occurrence can be reproduced well by simulation in which the end-member case of in-situ biogenic production of methane in the sediment of methane hydrate zone is set. The distribution pattern of hydrate saturation is basically controlled by that of TOC. However, the hydrate concentration near the bottom of the hydrate zone is increased by the effect of recycling of dissociated methane of pre-existing hydrate. No hydrate zone expresses the geologic time needed until the local concentration of methane exceeds the solubility by gradual accumulation of in-situ biogenic methane with burial.

A mathematical model for the formation and dissociation of methane hydrates in the marine environment

“…The hydrate accumulation at site 997 has previously been modeled by Xu and Ruppel [1999], Davie and Buffett [2001, 2003a, 2003b], Nimblett and Ruppel [2003], and Baba and Katoh [2004]. Xu and Ruppel [1999] used a steady state analytical model to estimate the upward methane flux required for the base of the hydrate occurrence zone to coincide with the bottom of the hydrate stability zone and the top of the free gas zone.…”

“…To model the inferred hydrate volume, Davie and Buffett [2001] had to assume a rather high value (1.1%) for the available organic carbon at the seafloor. Baba and Katoh [2004], using a one‐dimensional static model, found that the hydrate saturation at site 997 could be reproduced using an available organic carbon content of 0.78%. Hydrate accumulation due to migration of methane‐bearing fluids from a deeper source was investigated by Davie and Buffett [2003a, 2003b].…”

BSRs and Associated Reflections as an Indicator of Gas Hydrate and Free Gas Accumulation: An Example of Accretionary Prism and Forearc Basin System along the Nankai Trough, off Central Japan

“…A similar interpretation is given by mathematical simulation using 1-dimensional static model to simulate accumulation process of marine gas hydrate. In this simulation, strongly hydrated sediments can be calculated just above the free gas zone by setting upward migration of gas-bearing fluid below the BGHS (Baba and Katoh, 2004).…”

3‐D basin‐scale reconstruction of natural gas hydrate system of the Green Canyon, Gulf of Mexico

“…Reactive gas hydrate formation and accumulation in marine sediments was initially simulated using simple 1‐D models [e.g., Baba and Katoh , ; Davie and Buffett , ; Garg et al ., ; Katoh et al ., ; Rempel and Buffett , ]. Subsequently, these models were augmented to include the Anaerobic Oxidation of Methane (AOM) [e.g., Burwicz et al ., ; Chatterjee et al ., ; Egeberg and Dickens , ; Torres et al ., ; Wallmann et al ., ], the permeability evolution due to gas hydrates formation [ Nimblett and Ruppel , ; Seol and Kneafsey , ], and the influence of a free‐gas layer underlying gas hydrate deposits [ Bhatnagar et al ., ].…”