Growth and Decomposition Mechanism of Clathrate Hydrates in the Presence of Porous Media and Seawater: Experimental Validation

The natural gas entrapped in hydrate reservoirs could meet the global energy demand for centuries. In order to exploit this vast energy source at a commercial production rate, it is necessary to forecast the amount and physical behavior of the natural gas hydrates contained in the reservoirs. Toward this direction, we formulate a rigorous mathematical model to interpret the clathrate hydrate kinetics in reservoirs, mimicking the environment. The formulation considers precisely the effects of the central elements existing in marine and permafrost regions, i.e., seawater and porous media. Usually, the salt ions present in seawater impede hydrate growth by interfering in the formulation of a strong network of hydrogen-bonded water molecules, and they counteract the hydrate decay by facilitating the breakage of the hydrate-associated water network. This multifaceted behavior is taken into account by introducing a general activity term in the newly proposed dynamic driving force, i.e., the difference in the chemical potentials of the cavity-building water molecules in the liquid and hydrate phases. The same term accounts for the irregularities in the size and shape of the porous sand particles and their internal pores. Aside from this, we propose to use the active surfaces of unconsolidated porous materials as the interface for the phase transition. The formulation is finally implemented to predict the formation, growth and decomposition of methane and carbon dioxide hydrates in the presence of synthetic and natural seawater and silica sand with a range of particle sizes, over a wide range of operating pressure and temperature. It appears that the proposed formulation is reliable and sufficiently accurate in predicting the clathrate hydrate kinetics in the reservoir-like situation.