Dynamic multiphase flow model of hydrate formation in marine sediments

Abstract

[1] We developed a multicomponent, multiphase, fluid and heat flow model to describe hydrate formation in marine sediments; the one-and two-dimensional model accounts for the dynamic effects of hydrate formation on salinity, temperature, pressure, and hydraulic properties. Free gas supplied from depth forms hydrate, depletes water, and elevates salinity until pore water is too saline for further hydrate formation: Salinity and hydrate concentration increase upward from the base of the regional hydrate stability zone (RHSZ) to the seafloor, and the base of the hydrate stability zone has significant topography. In fine-grained sediments, hydrate formation leads to rapid permeability reduction and capillary sealing to free gas. This traps gas and causes gas pressure to build up until it exceeds the overburden stress and drives gas through the RHSZ. Gas chimneys couple the free gas zone to the seafloor through high-salinity conduits that are maintained at the three-phase boundary by gas flow. As a result, significant amounts of gaseous methane can bypass the RHSZ, which implies a significantly smaller hydrate reservoir than previously envisioned. Hydrate within gas chimneys lies at the three-phase boundary, and thus small increases in temperature or decreases in pressure can immediately transport methane into the ocean. This type of hydrate deposit may be the most economical for producing energy because it has very high methane concentrations (S h > 70%), located near the seafloor, which lie on the three-phase boundary.Citation: Liu, X., and P. B. Flemings (2007), Dynamic multiphase flow model of hydrate formation in marine sediments, J. Geophys.

A Two-Dimensional Post-Stack Seismic Inversion for Acoustic Impedance of Gas and Hydrate Bearing Deep-Water Sediments Within the Continental Slope of the Ulleung Basin, East Sea, Korea

“…10b) near and at UBGH09 and 10 is interpreted as a lobe of high-density, sand-rich mass-flow deposition disturbing the existing conformable layers of the THSs (Fig. 3); however, it may also be related to high-flux gas migrating through openings (Haacke et al 2009) which we have here as evidenced by the gas chimneys (Liu and Flemings 2007). Co-existence of hydrate and gas is not unusual Fig.…”

Controlled-source electromagnetic and seismic delineation of subseafloor fluid flow structures in a gas hydrate province, offshore Norway

“…We infer that the saturation of hydrate is higher in this upper region than elsewhere along the pipe structure and at the BGHSZ. High hydrate saturation at that location is probably due to preferential gas advection and interaction of the gas hydrate stability field with the free gas (Flemings et al 2003;Liu & Flemings 2007;Smith et al 2014). While high resistivities can result from both free gas and gas hydrate, high seismic velocities can only be caused by gas hydrate.…”

Reduced Numerical Model for Methane Hydrate Formation under Conditions of Variable Salinity. Time-Stepping Variants and Sensitivity

“…The latter is new and was not undertaken for the comprehensive model [4]. It is significant in that it guides the reader in the choice of optimal parameters and shows the robustness of the reduced model.…”

“…One of the advantages of this reduced model in contrast to fully comprehensive models such as in, e.g., [4], is that the reduced model is easy to implement and to extend, and is amenable to various analyses.…”