Stability analysis of the water bridge in organic shale nanopores: A molecular dynamic study

Abstract

In the last decades, shale gas development has relieved the global energy crisis and slowed global warming problems. The water bridge plays an important role in the process of shale gas diffusion, but the stability of the water bridge in the shale nanochannel has not been revealed. In this work, the molecular dynamics method is applied to study the interaction between shale gas and water bridge, and the stability can be tested accordingly. CO 2 can diffuse into the liquid H 2 O phase, but CH 4 only diffuses at the boundary of the H 2 O phase. Due to the polarity of H 2 O molecules, the water bridge presents the wetting condition according to model snapshots and one-dimensional analyses, but the main body of the water bridge in the two-dimensional contour shows the non-wetting condition, which is reasonable. Due to the effect of the molecular polarity, CO 2 prefers to diffuse into kerogen matrixes and the bulk phase of water bridge. In the bulk of the water bridge, where the interaction is weaker, CO 2 has a lower energy state, implies that it has a good solubility in the liquid H 2 O phase. Higher temperature does not facilitate the diffusion of CO 2 molecules, and higher pressure brings more CO 2 molecules and enhances the solubility of CO 2 in the H 2 O phase, in addition, a larger ratio of CO 2 increases its content, which does the same effects with higher pressures. The stability of the water bridge is disturbed by diffused CO 2 , and its waist is the weakest position by the potential energy distribution.

Mechanism Analysis of Shale Gas Adsorption under Carbon Dioxide–Moisture Conditions: A Molecular Dynamic Study

“…The main component of shale gas is CH 4 , and shale gas is a mixture that always contains an amount of moisture. − The moisture is generated by the gas migration and the thermal reaction of organic matter. − The content of moisture affects the development of shale gas, and the adsorption capacity of shale gas is inhibited by more moisture content. , In the past few years, carbon capture, utilization, and storage (CCUS) have been regarded as a direct way to reduce carbon pollution and slow global warming . The adsorption and diffusion processes of CH 4 and CO 2 in coal matrixes, which are similar to those of kerogen structures, were studied, , and the properties of organic matrixes will be affected by H 2 O and CO 2 . , The competitive adsorption of CH 4 and CO 2 was also studied in nanoconfined slits .…”

Microstructures and Pore Structures of Naturally Deformed Shales: Significance for Shale Gas Exploration in the Complex Tectonic Areas of the Margin of the Sichuan Basin, South China

“…Scholars have already conducted studies on pore characterization in different shales, in which it has been found that shale pore networks are dominated by organoporosity. − ,,, Consequently, we use intraparticle organic pores to illustrate why weakly deformed shales are mesopore-rich with low permeability and strongly deformed shales are macropore- and fracture pore-rich with high permeability, as shown in Figure . We assume that the micropores, mesopores, and macropores of the primary structural shale are all developed in a certain proportion and scale.…”

Wetting Behavior of Kerogen Surfaces: Insights from Molecular Dynamics

“…Kerogen is an essential part of the organic matter not soluble in common polar solvents. , The general consensus has been that kerogen is mainly hydrophobic; however, recent studies have observed that the presence of heteroatoms (polar nitrogen-, sulfur-, and oxygen-containing (NSO) compounds) in kerogen might induce a mixed-wet or even hydrophilic characteristics in kerogen, leading to an intricate wetting behavior of this matter. − Thus, obtaining an accurate knowledge of kerogen wettability and gaining better insight into how kerogen impacts fluid flow can profoundly help not only in production from unconventional shale but also in effective geological carbon sequestration (GCS) since shale reservoirs have shown promising results to act as CO 2 sinks. CO 2 can be stored in shale reservoirs through the residual or capillary trapping mechanism, by which carbon is trapped through high capillary forces in the porous media of the formation rock. , …”