PhD Defense Aslaug Clemmensen Glad

Most carbonate reservoirs are naturally fractured. Fractures can significantly influence a formation's geological and geomechanical conditions and act as barriers or conduits for fluid flow. The Valdemar Field (Danish Central Graben) is the Danish North Sea's third-largest producing oil field. Its reservoir is confined to the Lower Cretaceous Tuxen and Sola Formations and comprises interbedded chalk and marl facies, resulting in low permeability and high porosity. Thus, production relies on the presence of natural fractures to enhance the local permeability and form connected networks and migration routes for fluid flow.

This thesis is a geological examination of natural fractures in the Valdemar Field with emphasis on fracture characterization, geomechanical modeling, and assessment of the impact on reservoir properties. Fracture types, patterns, and densities are determined in sedimentary cores and are related to facies and stratigraphy. Based on core studies, a new revised reservoir zonation is proposed to account for lithological and geomechanical control on fracture distribution accurately. Fracture geometry, intensity, and connectivity are evaluated through X-ray computed tomographic (CT) imaging analysis of fractured cores and coupled with aperture distributions to characterize fracture types. Geomechanical-based discrete fracture network (DFN) simulations of fracture evolution and patterns across the reservoir highlight the variance in large-scale fracture distribution, connectivity, and anisotropy of the fractures.

These fracture patterns support the understanding of production in studied wells with known high or low production rates. This thesis contributes to the geological understanding and assessment of natural fractures in the Lower Cretaceous reservoir of the Valdemar Field.

Supervisors
Senior Researcher Hamidreza M. Nick, DTU Offshore
Associate Professor Ole R. Clausen, Aarhus University
Researcher Frédéric Amour, DTU Offshore

Examiners
Reader, Adriana Paluszny, Imperial College London
Dr. Ole V. Vejbæk, OVV Geoscience
Associate Professor Alexander Shapiro, DTU CERE