Multi-scale Characterisation of Fractures in Carbonate Reservoirs

Carbonate reservoirs commonly display fracture-controlled flow behaviour that cannot be understood from a single observation scale alone. This thesis develops and applies a multi-scale framework integrating seismic-, outcrop-, and microscale fracture observations to quantify fracture geometry, topology, and hydraulic significance in carbonate formations, with implications for hydrocarbon production and geological CO₂ storage. At the seismic scale, structural interpretation of the Razzak Field, northern Western Desert, Egypt, shows that the field is primarily controlled by moderate positive inversion superimposed on a Jurassic rift, rather than by wrench tectonics. Selective reverse reactivation of inherited faults influenced closure development, seal preservation, and likely fracture localisation. Building on this framework, an integrated workflow combining 3D seismic attributes, FracPaQ analysis, and well-log petrophysics was used to assess fracture distribution within the Aptian Alamein Formation. Results demonstrate that fracture intensity and connectivity are highest near inversion-related fault corridors, and that fracture porosity locally compensates for poor matrix porosity, strongly influencing reservoir quality and fluid-flow potential. At the outcrop scale, 3D fracture characterisation of the Eocene Thebes Formation, used as an outcrop analogue to the subsurface Aptian Alamein Formation, shows that 2D methods systematically underestimate fracture persistence and connectivity. High-resolution model reveals that steep E–W and NW-SE fracture sets form the dominant connected pathways supported by conjugate NE–SW fracture set, while mechanical stratigraphy exerts a first-order control on fracture organisation. At the fracture-surface micro-scale, numerical modelling of stress-dependent fracture aperture closure demonstrates that surface roughness strongly controls permeability evolution, hysteresis, and capillary sealing behaviour under stress paths relevant to CO₂ injection and storage. Overall, this thesis demonstrates that multi-scale integration can improve predictions of fracture-controlled permeability and connectivity. Although acquiring seismic, FMI, outcrop, and sample-scale datasets may not always be practical, their combined use where available helps reduce uncertainty and provides a transferable workflow for assessing how fault architecture, fracture connectivity, and stress-dependent fracture closure influence subsurface fluid flow.