Using Geomechanical Models to Simulate the Growth of the Fracture Network in the Ekofisk Formation of the Kraka Structure, Danish Central Graben

In this paper, we show how it is possible to create models of the fracture network across the Kraka structure dynamically, by simulating the physical processes of fracture nucleation, propagation and growth, based on the knowledge and insights of the previous papers in this volume. Forward modelling the fracture network in this way gives insights into the physical mechanisms and parameters that control fracture geometry, as well as providing high quality input for fluid flow and geomechanical simulations. To generate reliable results with this technique, it is essential to constrain the input parameters against measurements for well and seismic data. In this paper we use in situ stress data to constrain the time dependent mechanical properties such as horizontal stress and strain relaxation, and fracture logs from core and borehole images to constrain the initial seed fracture population. This is combined with mechanical property data from Amour et al. (this volume), and strain data from Petersen et al. (this volume) and Welch et al. (in Modelling the Evolution of Natural Fracture Networks. Springer Nature Switzerland AG, 2020), to run a series of sensitivity models on a small area of Kraka. The results of these models are compared with the lineaments observed on ant-tracked seismic data (Smit & Welch, this volume) and the fractures logged on borehole images (Aabø et al., 2020), to investigate the effect of factors such as the thickness of the fractured layer, the origin of the driving strain (flexural vs regional extension), and strike-slip displacement on the fracture geometry. Finally we run full-field models of the entire Kraka structure, using best estimate values for all parameters, and compare the results with the ant-tracked seismic lineaments and the fractures logged on borehole images, to show that the forward modelling technique is capable of generating detailed models that accurately represent the geometry of the fracture network, including properties such as anisotropy, connectivity and fracture length distribution that are key controls on fluid flow and geomechanics response.