Connectivity, permeability and flow channelization in fractured karst reservoirs: A numerical investigation based on a two-dimensional discrete fracture-cave network model

Xu Zhang, Zhaoqin Huang, Qinghua Lei, Jun Yao, Liang Gong, Shuyu Sun, Yang Li

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Fractured karst reservoirs play a significant role in hydrocarbon reserves and groundwater storage. They often exhibit complex multiscale heterogeneities involving pores, fractures and caves, whose length scales range from microns to tens or hundreds of meters. Thus, the study of fractured karst reservoirs is faced with a significant unresolved challenge in quantitatively characterizing the geometrical connectivity and hydraulic conductivity as well as their interrelationships in such strongly heterogeneous, multicomponent systems. In this paper, we propose an analytical formulation to characterize the connectivity of discrete fracture-cave networks building upon the excluded area concept of the percolation theory. By implementing a state-of-the-art computational model solving coupled Navier-Stokes (free flow) and Darcy (porous media flow) equations, we numerically derive the permeability of a fractured and karstified porous media, such that the relationship between the connectivity and permeability is further explored. The high-fidelity numerical model also permits us to elucidate the process of flow channelization within the fracture-cave network. The results show that the fracture-cave network connectivity correlates to the permeability via a power law scaling for connected systems. Significant flow channeling occurs around the percolation threshold where the flow is dominated by a limited number of preferential pathways. Caves play a crucial role in the flow due to the fact that caves could globally enhance the network connectivity and locally serve as hotspots for high fluid velocity. Finally, a semi-analytical permeability model for fractured karst reservoirs is developed. The results of our research and insights obtained have important implications for understanding the subsurface fluid flow in fractured karst reservoirs.
Original languageEnglish (US)
Pages (from-to)104142
JournalAdvances in Water Resources
Volume161
DOIs
StatePublished - Jan 26 2022

Bibliographical note

KAUST Repository Item: Exported on 2022-12-12
Acknowledged KAUST grant number(s): BAS/1/1351–01–01
Acknowledgements: This study was supported by Major Science and Technology Projects of China National Petroleum Corporation (ZD2019–183–008), Fundamental Research Funds for the Central Universities (18CX05029A) and Funding from King Abdullah University of Science and Technology (BAS/1/1351–01–01).

ASJC Scopus subject areas

  • Water Science and Technology

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