Visualising and modelling flow processes in fractured carbonate rocks with X-ray computed tomography

Abstract

Naturally Fractured Reservoirs (NFR) have typically very complex geometries from the pore scale to the field scale – discontinuities can be found at each scale. This makes NFRs hard to accurately be modelled for flow simulations. Fractures are especially difficult to incorporate in the simulations. The topology of a single fracture is usually simplified to a plane or disk, and apertures are usually averaged to be implemented in the simulation models. The fracture aperture distribution of a single fracture is already very heterogeneous though. Contact areas in fractures can detain flow, whereas connected fracture regions with larger apertures can result in preferred flow paths and lead to early breakthrough. To help understanding how well current Discrete Fracture and Matrix (DFM) models are suitable to retain fracture influences on flow in carbonates, this research project combines the simulation of miscible single-phase flow through fractures in carbonates with precise fracture measurements (comprising fracture aperture distributions and 3D topologies) and the visualization of real single and two-phase flow experiments in fractured carbonate cores. The simulation approach employs a DFM model with a hybrid finite element/ finite volume (FEFV) method. The fractured core samples and the flow experiments are imaged with high-resolution X-ray computer tomography (CT), or X-ray radiography respectively. The main goals are to develop and optimize an image processing workflow from the X-ray CT fracture measurement to an according mesh generation as input for simulations, and to be able to compare simulations and flow experiment studies qualitatively to analyse how well the DFM approach is able to capture the true nature of fluid flow in fractures with real aperture distributions. To obtain most relevant comparisons, we conduct numerical simulations and flow experiments on the same fracture geometries, which have been measured before non-destructively