Enhancing the Efficiency of Coal Bed Methane Recovery by Injecting Carbon Dioxide Based on an Anthracite Coal Macromolecular Model and Simulation Methods

Abstract

Enhancing the efficiency of coal bed methane (CBM) recovery by injecting carbon dioxide (CO2) is regarded as an effective method to exploit CBM, and CO2 geological sequestration also mitigates greenhouse gas emissions. In this study, 13C nuclear magnetic resonance (13C NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) experiments are employed to construct a two-dimensional (2D) chemical molecular structure. The 2D chemical molecular structure is annealed and geometrically optimized to construct a three-dimensional (3D) anthracite molecular model by molecular simulations. The CH4/CO2 mixed gas competitive adsorption and displacement of CH4 by injecting CO2 in an anthracite coal molecular model is investigated by Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The simulation results show that CO2 is easier to adsorb than CH4, which is conducive for CO2 to have an advantage in competitive adsorption at a temperature of 303.15 K and a pressure of 10 MPa. The total amount of CH4/CO2 mixed gas is higher in small pores than in large pores at a pressure of less than 1 MPa. Simultaneously, the MD simulation result reveals that the displacement efficiency of CH4 recovery by injecting 10 MPa CO2 into a 1 nm pore was enhanced by about 73.08% at the temperature of 303.15 K. These research results will help to realize CO2-enhanced coal bed methane (ECBM) recovery at the microscopic level and geological CO2 sequestration to reduce environmental pollution.

The Effectiveness of the Continuous and Cyclic Method on CO<sub>2</sub>-ECBM

“…The desorption curve experiences a decline indicating that only a limited number of methane molecules can desorb, with the residual gas being retained [30]. This condition worsens when small pores reach maximum adsorption capacity, leading to dominant swelling effects in the coal matrix [31]. Due to various factors, the CH 4 trapped in coal seams cannot be released smoothly, which may hinder CH 4 recovery improvement.…”

Molecular Dynamics Simulation of Methane Adsorption and Diffusion: A Case Study of Low-Rank Coal in Fukang Area, Southern Junggar Basin

“…Micropores and mesoporous pores in coal are the main adsorption sites for methane. In this paper, we used the 3D macromolecular structure as a basis, a 1 nm blank slit layer was constructed and the adsorption behavior of methane was studied using the large canonical ensemble Monte Carlo (GCMC) simulation method using the adsorption module in Materials Studio software (version 19.1.0.2353) [46,60].…”

The Relationship between Structure and Performance of Different Polyimides Based on Molecular Simulations

“…With the development of computer technology and simulation software, simulation technology has been shown to greatly reduce the cost of material development and improve work efficiency [ 21 , 22 , 23 , 24 , 25 , 26 ]. A molecular dynamic simulation optimization experiment showed that an efficiency ratio of running time that tended to balance judgment achieved the highest value of 36.96% [ 27 ].…”