Changes in Pore Structure of Coal Caused by CS₂ Treatment and Its Methane Adsorption Response

Abstract

The pore structure and gas adsorption are two key issues that affect the coal bed methane recovery process significantly. To change pore structure and gas adsorption, 5 coals with different ranks were treated by CS 2 for 3 h using a Soxhlet extractor under ultrasonic oscillation conditions; the evolutions of pore structure and methane adsorption were examined using a highpressure mercury intrusion porosimeter (MIP) with an AutoPore IV 9310 series mercury instrument. The results show that the cumulative pore volume and specific surface area (SSA) were increased after CS 2 treatment, and the incremental micropore volume and SSA were increased and decreased before and after R o,max = 1 3%, respectively; the incremental big pore (greater than 10 nm in diameter) volumes were increased and SSA was decreased for all coals, and pore connectivity was improved. Methane adsorption capacity on coal before and after R o,max = 1 3% also was increased and decreased, respectively. There is a positive correlation between the changes in the micropore SSA and the Langmuir volume. It confirms that the changes in pore structure and methane adsorption capacity due to CS 2 treatment are controlled by the rank, and the change in methane adsorption is impacted by the change of micropore SSA and suggests that the changes in pore structure are better for gas migration; the alteration in methane adsorption capacity is worse and better for methane recovery before and after R o,max = 1 3%. A conceptual mechanism of pore structure is proposed to explain methane adsorption capacity on CS 2 treated coal around the R o,max = 1 3%.

Effects of CS2 Solvent Extraction on Nanopores in Coal

“…The current research on CS 2 extracted coal mostly focuses on the coal chemical structure and the analysis of pores by a single method. ,, Significantly, the fractal evolution of the full-scale pore structure of CS 2 extracted coal is insufficient. The macropore fractal dimension D 1 , mesopore fractal dimension D 2 , and micropore fractal dimension D 3 were fitted according to Eqs.…”

Numerical Simulation Study of Fines Migration Impacts on an Early Water Drainage Period in Undersaturated Coal Seam Gas Reservoirs

“…Thirdly, the reduction of porosity due to deposition of coal fines is equal to the sum of the denudation volumes of the coal fines, which is expressed in Equation (17a). The permeability model of coal can be employed to describe the permeability damage induced by porosity [41][42][43][44], shown in Equation 17b:…”

Study of the Methane Adsorption Characteristics in a Deep Coal Reservoir Using Adsorption Potential Theory

“…As is well known, coalbed methane is present in the adsorbed state within the pores of a coal matrix and in a free state in coal pores and fractures, along with a small amount in a dissolved state in coal seam water [1][2][3]. The accumulation of coalbed methane is a prerequisite and foundation for its exploration and development [4]. From the 1980s to the early 21 st century, the exploration of coalbed methane with depths ranging from 1500 to 3000 m was conducted in North America [5][6][7].…”