192 / 2023-09-05 14:46:25

Numerical estimation of fracture network permeability based on GEOFRAC model for groundwater modeling in a tin mine

Discrete fracture network, geostatistics, permeability tensor, groundwater flow, fault distribution

Numerous geological research studies and mining operations have proved that fracture is one of the important factors controlling groundwater flow, mineralization and ore distribution in metallic deposits. most current approaches for groundwater flow simulation of naturally fractured media relies on the calculation of equivalent permeability tensors from a discrete fracture network. Simulating a discrete fracture network (DFN) in a mine area is therefore crucial to mine water inrush accidents and disaster prevention, resource exploration and underground mining safety. This study aimed to construct a plausible two-dimensional DFN using GEOstatistical FRACture simulation method (GEOFRAC), a geostatistical method of conditioning directions (strikes and dips) and locations of sample fractures, by selecting the northern part of the Gejiu tin district, southwest China, and using 3724 outcrop fractures sampled on the ground of mountain Gaosong. Geographically, the mining area is located in the southern part of the middle-Dian Plateau, an alpine hilly area. The mountains in the area are continuous, heavy and overlapping, and there is no obvious trend; they are mostly blocky mountains. The mountainous area accounts for 86% of the total area of the region. The Gaosong mine is situated in the northern part of the tin mine in Gejiu (Figure 1), which is restricted by the Gejiu and Jiajieshan Faults in a north–south direction and the Gesong and Beiyinshan Faults in an east–west direction, and is covered mainly by dolomite and dolomitic limestone of the middle Triassic with dispersed distribution of Tertiary mudstone and Quaternary residual deposits. The study area was a rectangular area of 17 km by 9 km that covered the Gaosong mining area. Critical parameters of this DFN are density, direction, and connective condition of discs that form a fracture plane. The simulated fractures were verified in that their directions corresponded well with those of the sample fractures. The permeability tensor of each modeling grid is then calculated based on the fracture network constructed.



The study planned to build a rational DFN in a metallic mining area by selecting the Gaosong mine in southwestern China to depict the relationship between fracture distribution and permeability tensor. The GEOFRAC method was validated by consistency of major tendencies in simulated fractures’ directions with those of outcrop sample data and positional agreement of the continuous fractures with the actual faults. GEOFRAC is confirmed as a convincing tool to generate a rational DFN that can describe restrictions of fractures on the groundwater flow path and contribute to prevention of mine water inrush accidents. The calculated permeability shows consistency with the main fractures and faults in the study area. Future works could reduce bias in sampled fractures direction, consider fractures widths for modeling more plausible DFN and to generate a more general fracture network with both ground network and underground network. By using such systematic fracture networks with calculated permeability, groundwater flow can be simulated in this tin mining area.