An Innovative Method to Evaluate Hydraulic Conductivity of a Single Rock Fracture Based on Geometric Characteristics

Geometry of a single fracture has significant influence on the fluid flow in fractured rocks. However, quantification of geometry–flow relationship in a rock fracture is still far from being completed. The primary goal of this study was to identify a few key geometric parameters for quantifying its impact on fluid flow in a single rock fracture and then to evaluate its hydraulic conductivity. The concept of a threshold aperture is first introduced to estimate the effective area involved in the flow process in a single rock fracture. It is assumed that only those zones with greater apertures than a threshold value are involved in the flow process. The effect of variable aperture distributions on flow in a single rock fracture is quantified based on the cumulative distribution of individual apertures of sampling points. The surface roughness is decomposed into primary roughness (i.e. the large-scale waviness of the fracture morphology) and secondary roughness (i.e. the small-scale unevenness) with a wavelet analysis. The influence of surface roughness on the fluid flow in a single rock fracture is quantified with the normalized area of primary roughness and the standard deviation of secondary roughness. By combining the variable aperture distributions and the surface roughness on flow, an empirical equation to estimate the intrinsic hydraulic aperture and hydraulic conductivity of a single rock fracture is proposed. In addition, a series of high-precision hydraulic tests are conducted on 60 artificial tensile fractures to verify the proposed equation. The results show that the proposed equation predicts the intrinsic hydraulic aperture and hydraulic conductivity of a single rock fracture very well.