Characterization of Pore Structures with Mercury Intrusion Porosimetry after Electrochemical Modification: A Case Study of Jincheng Anthracite

Quantitative characterization of the change in the cleat and pore structures and fractal dimensions in anthracite after electrochemical modification is crucial for better understanding of the modification effect. Thus, lump anthracite samples were electrochemically modified in our manufactured device with 0, 0.5, 1, and 2 V/cm potential gradients. The changes in heterogeneity and porosity after modification were tested and analyzed by mercury intrusion porosimetry (MIP) and fractal theory. The results indicated that the total volume of the pores increased after electrochemical treatment and continuously increased with increasing potential gradient during the treatment process. After modification, the number of pores or fractures with a pore size between 6 and 20 μm in coal after modification increases significantly. According to the intrusion pressure, three stages were defined as lower (PM < 0.1 MPa), intermediate (0.1 ≤ PM < 10 MPa), and higher regions (PM ≥ 10 MPa), which are characterized by fractal dimensions D1, D2, and compression stages, respectively. After modification, the fractal dimension D1 showed an increasing trend, while the fractal dimension D2 showed a decreasing trend, indicating that the fracture system became more complicated and that the pore system became more regular after electrochemical treatment. The evolution mechanism of heterogeneity and porosity and their fractal dimensions were explained by the dissolution of minerals, change in pH values, and dynamics of temperatures during the process of modification. The results obtained in this work are of important guiding significance for coalbed methane (CBM) extraction via in situ modification by electrochemical treatment.