Modelling Methane Hydrate Saturation in Pores: Capillary Inhibition Effects

Abstract

Experimental and field observations evidence the effects of capillarity in narrow pores on inhibiting the thermodynamic stability of gas hydrates and controlling their saturation. Thus, precise estimates of the gas hydrate global inventory require models that accurately describe gas hydrate stability in sediments. Here, an equilibrium model for hydrate formation in sediments that accounts for capillary inhibition effects is developed and validated against experimental data. Analogous to water freezing in pores, the model assumes that hydrate formation is controlled by the sediment pore size distribution and the balance of capillary forces at the hydrate–liquid interface. To build the formulation, we first derive the Clausius–Clapeyron equation for the thermodynamic equilibrium of methane and water chemical potentials. Then, this equation is combined with the van Genuchten’s capillary pressure to relate the thermodynamic properties of the system to the sediment pore size distribution and hydrate saturation. The model examines the influence of the sediment pore size distribution on hydrate saturation through the simulation of hydrate formation in sand, silt, and clays, under equilibrium conditions and without mass transfer limitations. The results show that at pressure–temperature conditions typically found in the seabed, capillary effects in very fine-grained clays can limit the maximum hydrate saturation below 20% of the host sediment porosity.

Study of the Critical Pore Radius That Results in Critical Gas Saturation during Methane Hydrate Dissociation at the Single-Pore Scale: Analytical Solutions for Small Pores and Potential Implications to Methane Production from Geological Media

“…The particular problem bears similarities with the "liquid-to-gas" phase change problem that is encountered in the drying/evaporation of porous media, which has been discussed in detailed in [77][78][79]. Additionally, it should be noted that P-T diagrams of real geological media, which also indicate the shift of the hydrate equilibrium curves, can be found in the studies of Liu and Flemings [80] and De La Fuente et al [59]. Condition for Gas Bubble Growth and Production.…”

“…Such works were reported, among others by Clarke et al [50], Klauda and Sandler [12,51], Peddireddy et al [52], Sun and Duan [53], Song et al [54], and Duan et al [55], Li et al [56], Zarifi et al [37], Zhou et al [57], and Azimi et al [58]. An additional discussion and related references on the effect of the capillarity in narrow pores on the hydrate equilibrium conditions can be found in the recent study by De La Fuente et al [59].…”

Seismic Characterisation of Multiple Bsrs in the Eastern Black Sea Basin

“…Assuming hydrostatic pore fluid pressure and steady state temperature conditions, this calculation depends upon parameters such as the bathymetry, geothermal gradient, seafloor temperature, pore-water salinity, and molecular composition of the hydrate forming gas (e.g., Sloan, 1998). Other parameters affecting hydrate stability such as pore size (e.g., Østergaard et al, 2002;De La Fuente et al, 2021) are not considered here.…”

A Geomechanical Model for Gas Hydrate Bearing Sediments Incorporating High Dilatancy, Temperature, and Rate Effects

“…Methane hydrates are crystalline structures consisting of methane trapped in frozenwater molecules cages (e.g., [1,2]). They are stable at high pressure (P) and low temperature (T), and are generally found in seabed sediments and permafrost settings in the hydrate (P-T) stability zone.…”