Review of visualisation methods of studying the seepage mechanism in fractured rocks

The accurate measurement of characteristic parameters of fracture structures and fluid flow is an essential prerequisite for understanding the seepage mechanism of complex fracture systems. This paper discusses the research progress on the characteristic parameters measured in seepage tests of the real rock, the transparent rock and the digital rock from the perspective of visualisation. Firstly, the studies on the measurement of rock permeability without considering fractures, the seepage experiment with single fractures, the characterisation of complex fracture structures and the auxiliary visualisation of seepage experiments are reviewed. Secondly, the preparation method of transparent rocks and the measuring method of the fluid flow process in transparent rocks are summarised. Thirdly, digital modelling methods for complex fractured rocks and numerical simulation methods for seepage tests in fractures are reviewed. Finally, this paper proposes recommendations for revealing the seepage mechanism of complex fracture systems through the visual measurement method.