Gas hydrates are ice-like crystalline solids in which water molecules trap gas molecules in clathrate structures. They can preserve in low temperatures and elevated pressures and may exist in permafrost or deep marine environments. Natural gas hydrates are especially sensitive to the changes in temperature and pressure due to environmental changes. This can result in hydrate decomposition, which in turn may release enormous amounts of CH4 as the main component of natural gas hydrates. This study was an effort to use the molecular simulations for the estimation of possible gas release from the destabilization of natural gas hydrate reservoirs in response to environmental changes.
The dissociation data for simple CH4 hydrates, CH4-C3H8 hydrates and CH4-C2H6-C3H8-CO2 mixed hydrates were provided by using molecular dynamics (MD) simulations. The MD simulations could provide a better understanding of the phenomena involved in the dissociation process of gas hydrates and help to explain the experimental observations. It would be one of the best molecular simulation tools for calculating time-dependent properties.
The simple CH4 form structure I (sI) hydrates, while the above-mentioned binary and multicomponent gas mixtures can form structure II (sII) hydrates. Different simulation boxes were designed based on the structures and guest molecules of the gas hydrates. The simulation for CH4 hydrates was done via thermal stimulation above the ice point and depressurization below the ice point. For the mixed hydrates, the simulation data were only provided via thermal stimulation above the ice point. The dataset showed the simulation source files as well as the calculated time-dependent properties of gas hydrates upon the dissociation process. This included the simulation trajectories, gas density profiles, order parameters, ratios of large-to-small cavities, normalized rates of cavity decomposition, and gas compositions.
This dataset contains the inputs/outputs of four simulation runs which include the molecular coordinate and structure (.gro file) and trajectory (.xtc file), as well as the calculated time-dependent properties (.vmd and .xls files) for each run. The simulation time and length were presented in nanoseconds (ns) and nanometers (nm), respectively. Further details on the simulation methodology, procedures, and calculations have been provided in the following sections.
The guest molecule exchange of methane (CH4) by carbon dioxide (CO2) in natural gas hydrate reservoirs is considered a desirable possibility to produce CH4 and at the same time sequester CO2. So far process evaluation is commonly based on CH4-CO2 exchange yields and rates from small- or medium-scale experiments in partly water-saturated sediments, both of which does not represent natural conditions. The experiments are presented in detail in a currently submitted manuscript by Heeschen et al. (2019).
The presented data originate from two large-scale experiments (210 L) investigating the efficiency of the CH4-CO2 exchange under fully water-saturated natural reservoir conditions. For details on the equipment and the methods used see: Priegnitz et al., 2013; Schicks et al., 2011; Spangenberg et al., 2014. The reservoir conditions were 13 MPa and 8 °C, and the gas hydrate saturation in the sand (Sh) was 50% of the pore space. The gas hydrate was formed from dissolved CH4 only. About 50 kg heated CO2 was injected 1) discontinuously with intermediate soaking periods (E1) and 2) continuously (E2). In both cases, the CO2 injection periods were followed by a discontinuous depressurization of the reservoir.
The experiments demonstrate the importance of fluid migration patterns, heat transport, sample inhomogeneity, reaction kinetics, and secondary gas hydrate formation in water-saturated sediments. Methane production yields of 5% were small in both experiments during the injection periods, whereas controlled depressurization following the injection of CO2 into a CH4 hydrate reservoir could be a possible approach for the production of CH4 from a gas hydrate reservoir. However, the success of this method strongly depends on the distribution of CO2, and the availability and distribution of residual pore water.