A Connectivity Metrics-Based Approach for the Prediction of Stress-Dependent Fracture Permeability

Abstract

Rapid and accurate assessment of fracture permeability is critical for subsurface resource and energy development as well as rock engineering stability. Fracture permeability deviates from the classical cubic law under the effect of roughness, geological stress, as well as mining-induced stress. Conventional laboratory tests and numerical simulations are commonly costly and time-consuming, whereas the use of a connectivity metric based on percolation theory can quickly predict fracture permeability, but with relatively low accuracy. For this reason, we selected two static connectivity metrics with the highest and lowest prediction accuracy in previous studies, respectively, and proposed to revise and use them for fracture permeability estimation, considering the effect of isolated large-aperture regions within the fractures under increasing normal stress. Several hundred fractures with different fractal dimensions and mismatch lengths were numerically generated and deformed, and their permeability was calculated by the local cubic law (LCL). Based on the dataset, the connectivity metrics were counted using the revised approach, and the results show that, regardless of the connectivity metrics, the new model greatly improves the accuracy of permeability prediction compared to the pre-improved model, by at least 8% for different cutoff aperture thresholds.

Study on the Thermal Expansion Characteristics of Coal during CO2 Adsorption

“…The coal matrix releases heat during CO2 adsorption, leading to thermal expansion, and absorbs heat and contracts during CO2 desorption, resulting in a change in fracture width (Figure 6). To characterize the relationship between fracture width and permeability, the cubic law [22] can be utilized to depict the seepage behavior within a single fracture. The fracture is abstracted as a parallel plate with a certain opening.…”

“…The fr ture is abstracted as a parallel plate with a certain opening. Under the influence of a sta equilibrium pressure gradient, the cubic law expression derived from the Navier-Stok equations is as follows: To characterize the relationship between fracture width and permeability, the cubic law [22] can be utilized to depict the seepage behavior within a single fracture. The fracture is abstracted as a parallel plate with a certain opening.…”