Processing and Conversion of Raw Point-Cloud Laser Measurements and Auxiliary Data of Rough-Surfaced Fractures To Generate Corresponding Fracture Aperture Fields

Abstract

Abstract Understanding subsurface flow mechanisms in fractured rock is essential for subsurface infrastructure industries and geoscientific research. It is common to explore this using numerical modelling, however recently there are studies now replicating fractures by making use of 3D printing technologies. In order to produce a fracture replica, data from a real rock surface must be provided and an aperture field obtained. This data can be used for both 3D printing and numerical modelling and has the advantage of providing a direct correspondence between the 3D printed and numerical aperture field. In this study scans of the upper and lower surface of four 100 mm by 70 mm fracture cases were provided as point-cloud data. Pressure film data was also provided showing the pressure distribution across the aperture field at 5MPa of normal load. The scanning method results in an irregular mesh when looking for instance on the XY coordinate plane. This means the nodes of the upper and lower surface of the same fracture will not coincide. Due to this, the surface data is linearly interpolated onto a regular grid with a resolution of 0.1mm in order to easily obtain the aperture field. Issues arise from the vertical referencing of the upper and lower surface scans, resulting in unrealistic aperture field distributions. To correct this the lower surface is translated relative to the upper surface to improve alignment and reduce inaccurate negative values. However, this was insufficient to fully correct the aperture field, so the pressure film is used as a reference to vertically shift the upper surface until a visual best fit aperture field distribution is achieved. Once the aperture is obtained it can be used for numerical modelling and 3D printing. This study provides an example methodology for converting raw point-cloud data to a meaningful data set for representation of fracture apertures, as well as highlighting limitations and factors to consider during the process.