Effect of Kerogen Maturity, Water Content for Carbon Dioxide, Methane, and Their Mixture Adsorption and Diffusion in Kerogen: A Computational Investigation

Abstract

The adsorption behavior of CO 2 , CH 4 , and CO 2 /CH 4 mixtures in four different mature kerogens in the absence/ presence of water was studied using grand canonical Monte Carlo and classical molecular dynamics methods. The results exhibit that the adsorption isotherms of single-component CO 2 or CH 4 in kerogen present similar trends and show type I Langmuir adsorption behavior according to the IUPAC classification; the total adsorbed amount of both gases follows the order of type II-A < type II-B < type II-C < type II-D kerogen under the same conditions. The changing behavior of isosteric heat decreases first and then increases, which can explain the heterogeneous characteristic of the kerogen pore surface. The Coulombic and van der Waals interactions between CO 2 and kerogens play an important role on adsorption, while for CH 4 adsorption, the electrostatic effect is very small, even negligible. The N-, S-, and O-containing groups in kerogen have more remarkable influence on adsorption of CO 2 than CH 4 because of their strong adsorption energy, therefore notably improving the selectivity of CO 2 over CH 4 and following the order of type II-A > type II-B > type II-C > type II-D, which is beneficial to carbon capture and storage. Both pressure and temperature have an obvious impact on gas molecule diffusion, and low pressure and high temperature correspond to a large diffusion coefficient. In addition, preabsorbed water has a negative effect on the adsorption of CO 2 /CH 4 , and for the same amount of water molecules, the effect follows the order of type II-A > type II-B > type II-C > type II-D kerogens. The binding energy of water−kerogen is stronger than that of pure CH 4 or CO 2 −kerogen. The selectivity of CO 2 over CH 4 on kerogen increases with an increasing water content.

Molecular Dynamics Study on CO2 Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

“…We use type II kerogen with four different degrees of maturity (types II-A, II-B, II-C, and II-D) associated with three pore sizes (1, 2, and 4 nm) to represent slit-shaped kerogen nanopores. While there have been studies on water and CO 2 adsorption in the kerogen matrix, − we use slit-shaped kerogen nanopores to study the structural properties of CO 2 and water as such a geometry is one of the most common pore shapes in kerogen . The temperature and pressure are 353 K and 187.2 ± 2.2 bar, respectively, which are the typical shale reservoir conditions. , …”

Effects of a Viscoelastic Surfactant on Supercritical Carbon Dioxide Thickening for Gas Shale Fracturing

“…After the topology of the molecular shale model was built, the Grand Canonical Monte Carlo method was implied to simulate the adsorption of methane, Sc-CO 2 , and thickened Sc-CO 2 using N -ETFOSA and N , N , N ′-TM-1,3-PDA, respectively, on the molecular shale model built into slit pores. To calculate Coulombic interactions, the Ewald summation approach and atom-based van der Waals interactions were implemented, and an Andersen thermostat was imposed on the temperature control. , For energy minimization and equilibration, stages have been calculated and analyzed by Forcite calculation where canonical ensemble NVT and isobaric isothermal ensemble NPT were used simultaneously. For attaining the equilibrium state at every pressure point of adsorption isotherm, first, 5 × 10 6 steps are executed and, on the other hand, 1 × 10 7 steps are required for the production stage.…”

“…To calculate Coulombic interactions, the Ewald summation approach and atom-based van der Waals interactions were implemented, and an Andersen thermostat was imposed on the temperature control. 57,58 For energy minimization and equilibration, stages have been calculated and analyzed by Forcite calculation where canonical ensemble NVT and isobaric isothermal ensemble NPT were used simultaneously. For attaining the equilibrium state at every pressure point of adsorption isotherm, first, 5 × 10 6 steps are executed and, on the other hand, 1 × 10 7 steps are required for the production stage.…”

A Review on the Role of Organic Matter in Gas Adsorption in Shale

“…Sui et al 79 studied the adsorption capacity of CO 2 , CH 4 , and CO 2 /CH 4 mixtures in various kerogen types with and without the presence of water, using the GCMC and CMD methods. They established that the adsorption capacity is highest in Type II-A, followed by Type II-B and Type II-C kerogen, and is lowest in Type II-D kerogen.…”