In this study we compare the use of kinetic and equilibrium reaction models in the simulation of gas (methane) hydrate behavior in porous media. Our objective is to evaluate through numerical simulation the importance of employing kinetic versus equilibrium reaction models for predicting the response of hydrate-bearing systems to external stimuli, such as changes in pressure and temperature. Specifically, we (1) analyze and compare the responses simulated using both reaction models for natural gas production from hydrates in various settings and for the case of depressurization in a hydrate-bearing core during extraction; and (2) examine the sensitivity to factors such as initial hydrate saturation, hydrate reaction surface area, and numerical discretization. We find that for large-scale systems undergoing thermal stimulation and depressurization, the calculated responses for both reaction models are remarkably similar, though some differences are observed at early times. However, for modeling short-term processes, such as the rapid recovery of a hydrate-bearing core, kinetic limitations can be important, and neglecting them may lead to significant under-prediction of recoverable hydrate. The use of the equilibrium reaction model often appears to be justified and preferred for simulating the behavior of gas hydrates, given that the computational demands for the kinetic reaction model far exceed those for the equilibrium reaction model.

Comparison of kinetic and equilibrium reaction models in simulating gas hydrate behavior in porous media

Mechanical properties of remolded hydrate-bearing clayey-silty sediments

Effects of surface property of mixed clays on methane hydrate formation in nanopores: A molecular dynamics study.

Microscopic Molecular Insights into Methane Hydrate Growth on the Surfaces of Clay Minerals: Experiments and Molecular Dynamics Simulations

In this paper, the impact of initial water saturation (Siw) and multiple repetitive formations on the formation process of CH4 hydrate in silty clay sediments was examined in a homemade high-pressure visual reactor. The silty clay sediments were from the Shenhu area of the South China Sea. The results showed that the saturation of the CH4 hydrate decreased with the increase of Siw when they were at the same formation time. When the Siw’s were 50% and 60%, the formation process of the CH4 hydrate could be divided into two stages: a rapid formation stage and a slow formation stage. When the Siw was greater than 75%, the formation rate of the hydrate was just in a slow stage. After three repeated formation experiments were performed, we found that the saturation of the CH4 hydrate in the silty clay sediments increased with the time of the repeated experiments. Through camera observation, it was found that the repeated formation and dissociation process produced fractures or cracks in the sediment, which is conducive to reducing the resistance of the gas–liquid transport, providing space for the hydrate formation and storage, and increasing the porosity and hydrate saturation. The CH4 hydrate in the silty clay sediments occurred in the form of a disseminated or thin covering, and the hydrate saturation was from 11.2% to 60.8%, which covered the major hydrate core samplings from the Shenhu area of the South China Sea. The influential factors of forming a high CH4 hydrate saturation are interpreted and discussed in this paper. 

Experiment and Observation of Methane Hydrate Formation in Silty Clay Sediments of the South China Sea with 50–85% Water Saturation

Experimental and Numerical Analysis of the Effects of Clay Content on CH4 Hydrate Formation in Sand

This study explores the relationships that sedimentation rate and transport properties have with the formation and evolution of hydrates in fine-grained marine sediments and their corresponding bottom simulating reflector (BSR) responses. Using a series of one-dimensional simulations of multiphase, multicomponent flow and transport of mass and heat through porous media, a slab of sediments through sedimentation is modeled. The boundary conditions are set to emulate the pressure and geothermal gradients and its resulting gas hydrate stability zone (GHSZ). Hydrates are formed by injecting methane gas through the bottom of the grid and letting it migrate and reach the boundary of stability. The resulting hydrate accumulation is subjected to different sedimentation rates and replicated with different intrinsic permeability. With sedimentation, the geothermal gradient is displaced upward and the boundary of stability shoals. Through methane recycling, the distribution of phases changes through cycles of slow melting and rapid reformation. This results in a dynamic flow barrier that relocates the base of the GHSZ over geological time, in response to the variations of both pressure and salinity. The characteristics of a BSR response will be tied to the stage of the melting cycle. 

Alejandro Bello-Palacios

Papers

Experimental and Numerical Analysis of the Effects of Clay Content on CH4 Hydrate Formation in Sand

Modeling the Effects of Sedimentation on Natural Occurrences of CH4 Hydrates in Marine Sediments

Effects of methane hydrates on two-phase relative permeability in sandstone: Numerical simulation of laboratory experiments