Experimental Investigation of Gas Flow and Hydrate Formation Within the Hydrate Stability Zone

Abstract

We form methane hydrate by injecting methane gas into a brine‐saturated, coarse‐grained sample under hydrate‐stable thermodynamic conditions. Hydrate forms to a saturation of 11%, which is much lower than that predicted assuming three‐phase (gas‐hydrate‐brine) thermodynamic equilibrium (67%). During hydrate formation, there are temporary flow blockages. We interpret that a hydrate skin forms a physical barrier at the gas‐brine interface. The skin fails periodically when the pressure differential exceeds the skin strength. Once the skin is present, further hydrate formation is limited by the rate that methane can diffuse through the solid skin. This process produces distinct thermodynamic states on either side of the skin that allows gas to flow through the sample. This study illuminates how gas can be transported through the hydrate stability zone and thus provides a mechanism for the formation of concentrated hydrate deposits in sand reservoirs. It also illustrates that models that assume local equilibrium at the core‐scale and larger may not capture the fundamental behaviors of these gas flow and hydrate formation processes.

Mechanisms of Methane Hydrate Formation in Geological Systems

“…This model was conceptually described by Ginsburg () and Soloviev and Ginsburg () and is similar to the hydrate shell theory used to describe the interactions between gas and water in bubble systems (Rehder et al, ). Meyer et al () and Sahoo et al () demonstrated the presence of hydrate shells and the diffusion‐limited hydrate formation with laboratory‐controlled experiments in porous media. This model is also very similar to the coupled thermodynamic simulations of Fu et al ().…”

Introduction to Special Issue on Gas Hydrate in Porous Media: Linking Laboratory and Field‐Scale Phenomena

“…The role of a vapor phase in the nucleation and accumulation of gas hydrate in porous media is the focus of several laboratory studies in the Special Section as well (Meyer, Flemings, & DiCarlo, , Meyer, Flemings, DiCarlo, You, et al, ; Sahoo et al, ). Both Meyer, Flemings, DiCarlo, You, et al () and Sahoo et al () describe experiments in which gas hydrate does not form to saturations as high as are predicted based on thermodynamic equilibrium for the three phase system (gas‐pore fluid‐gas hydrate).…”

“…The role of a vapor phase in the nucleation and accumulation of gas hydrate in porous media is the focus of several laboratory studies in the Special Section as well (Meyer, Flemings, & DiCarlo, , Meyer, Flemings, DiCarlo, You, et al, ; Sahoo et al, ). Both Meyer, Flemings, DiCarlo, You, et al () and Sahoo et al () describe experiments in which gas hydrate does not form to saturations as high as are predicted based on thermodynamic equilibrium for the three phase system (gas‐pore fluid‐gas hydrate). Meyer, Flemings, DiCarlo, You, et al () start with methane migrating through the sediment sample already held within the P‐T conditions for hydrate stability, whereas Sahoo et al () inject methane gas and then allow the system to equilibrate before lowering the temperature, following a method first described by (Waite et al, ).…”

“…Both Meyer, Flemings, DiCarlo, You, et al () and Sahoo et al () describe experiments in which gas hydrate does not form to saturations as high as are predicted based on thermodynamic equilibrium for the three phase system (gas‐pore fluid‐gas hydrate). Meyer, Flemings, DiCarlo, You, et al () start with methane migrating through the sediment sample already held within the P‐T conditions for hydrate stability, whereas Sahoo et al () inject methane gas and then allow the system to equilibrate before lowering the temperature, following a method first described by (Waite et al, ). These studies and Meyer, Flemings, and DiCarlo () postulate that gas hydrate initially forms as a film or skin around gas bubbles in pore spaces.…”

“…Meyer, Flemings, and DiCarlo () interpret this finding by noting that lower methane flux allows more time for hydrate growth and the formation of thicker hydrate skins on gas bubbles, but also larger pressure differentials. The laboratory studies (Meyer, Flemings, & DiCarlo, , Meyer, Flemings, DiCarlo, You, et al, ; Sahoo et al, ) imply that gas bubbles may sometimes be stranded within pore space, armored by hydrate skins, and therefore unconnected to the flow of pore fluid and gas through the medium. Like the dissolved phase models of VanderBeek and Rempel (), the laboratory experiments conducted by Meyer, Flemings, & DiCarlo, (), Meyer, Flemings, DiCarlo, You, et al, () and Sahoo et al () with a free gas phase can provide an explanation, albeit with a different physical grounding, for high saturations of gas hydrate forming far above the base of the GHSZ.…”