A Physical Parameter Characterizing Heterogeneity of Pore and Fracture Structures in Coal Reservoirs

Abstract

Pore structure heterogeneity of coal reservoirs restricts the diffusion-seepage process of coalbed methane, thereby restricting the production capacity of coalbed methane. Therefore, 10 coal samples from the Linxing area are taken as an objective, and high-pressure mercury intrusion testing was used to describe the pore structure distribution of all the coal samples. On this basis, four single and multifractal models were used to perform fractal calculations, and correlation analysis was conducted on the mercury advance and retreat fractal dimension values to clarify the physical significance of mercury removal fractal dimension values. Finally, the relationship between fractal dimension values of mercury curves and pore structure parameters was clarified, and the applicability of various fractal models in characterizing pore structure heterogeneity was explored. All the samples can be divided into type A and B by using pore volume percentage greater than 1000 nm and the mercury removal efficiency. The T model has universality and the strongest correlation in characterizing the heterogeneity of pore volume distribution in samples. A fractal parameter based on high-pressure mercury injection curve was obtained, and was then used to quantitatively characterize the pore and fracture structure of coal reservoirs. This parameter is used to characterize the complexity of gas and water transport during coalbed methane production, further elucidating the coalbed methane production process under the constraint of pore and fracture structure in coal reservoirs.