Molecular Modeling of CO2 and n-Octane in Solubility Process and α-Quartz Nanoslit

Abstract

After primary and secondary oil recovery, CO 2 -enhanced oil recovery (EOR) has become one of the most mentioned technologies in tertiary oil recovery. Since the oil is confined in an unconventional reservoir, the interfacial properties of CO 2 and oil are different from in conventional reservoirs, and play a key role in CO 2 EOR. In this study, molecular dynamics simulations are performed to investigate the interfacial properties, such as interfacial tension, minimum miscibility pressure (MMP), and CO 2 solubility. The vanishing interfacial tension method is used to get the MMP (~10.8 MPa at 343.15 K) which is in agreement with the reported experimental data, quantitatively. Meanwhile, the diffusion coefficients of CO 2 and n-octane under different pressures are calculated to show that the diffusion is mainly improved at the interface. Furthermore, the displacement efficiency and molecular orientation in α-quartz nanoslit under different CO 2 injection ratios have been evaluated. After CO 2 injection, the adsorbed n-octane molecules are found to be displaced from surface by the injected CO 2 and, then, the orientation of n-octane becomes more random, which indicates that and CO 2 can enhance the oil recovery and weaken the interaction between n-octane and α-quartz surface. The injection ratio of CO 2 to n-octane is around 3:1, which could achieve the optimal displacement efficiency.

Factors Governing the Enhancement of Hydrocarbon Recovery via H2S and/or CO2 Injection: Insights from a Molecular Dynamics Study in Dry Nanopores

“…On silica, CO 2 yields an angle of ∼75° to the surface. A similar orientation of CO 2 has been previously reported on silica . For muscovite and MgO, in the models considered here, CO 2 lays parallel to the surface.…”

“…A similar orientation of CO2 has been previously reported for silica. 23 For muscovite and MgO, in the models considered here, CO2 lays parallel to the surface. On the other hand, H2S on muscovite is almost in 2-hydrogen down orientation, while on silica and MgO its orientation seems to be with either one hydrogen towards the surface or parallel to it.…”

“…Several studies have been reported in the literature concerning efforts directed towards understanding the mechanisms responsible for CO 2 -based EOR. ,,,− In general, the enhancement of hydrocarbon recovery is either attributed to preferential adsorption of CO 2 on the pore surfaces ,− or the dissolution of CO 2 in oil, which swells the oil and reduces its viscosity. ,− Previous research from our group reported that CO 2 preferentially adsorbs on silica surfaces, weakening n -butane adsorption and effectively acting as a “molecular lubricant” that lowers the activation energy for n -butane diffusion. Santos et al conducted molecular dynamics (MD) simulations in slit-shaped calcite pores to study the effect of CO 2 on n -alkane displacement.…”

Molecular Insight into Microbehaviors of n-Decane and CO2 in Mineral Nanopores

“…Liquid hydrocarbon (octane) static properties within quartz nanopores were explored by molecular dynamics (MD) simulations, which observed the layering structure of confined octane and concluded that the octane properties (e.g., density, self-diffusion coefficient, and viscosity) have a tendency to be bulk-liquid-like in the center of slits having apertures greater than 3.6 nm in size. Molecular simulations of CO 2 and oil mixtures in quartz, organic matter, silica, , and calcite nanoslits have been performed to investigate their structural and dynamical properties. Le et al have studied the competitive adsorption and diffusion of mixtures containing n -octane and CO 2 confined in slit-shaped silica and found that CO 2 preferential adsorption to the pore surface is likely to attenuate the surface adsorption of n -octane, lower the activation energy for n -octane diffusivity, and consequently enhance n -octane mobility at low CO 2 loading.…”

Competitive adsorption and reduced mobility: N-octane, CO2 and H2S in alumina and graphite pores

“…Several studies have been conducted for CO 2 -hydrocarbon systems confined in inorganic [13][14][15][16][17][18][19][20][21] and carbon nanopores [7,12,[22][23][24][25]. Yuan et al [23] performed MD simulations to study methane (CH 4 ) and CO 2 in carbon nanopores and found that CO 2 is more strongly adsorbed on graphite than CH 4 , resulting in CO 2 displacing CH 4 from the graphite surface.…”