Abstract: Fractures are ubiquitous in the subsurface, and they provide dominant pathways for ﬂuid ﬂow in low permeability formations. Therefore, fractures usually play an essential role in many engineering ﬁelds, such as hydrology, waste disposal, geother-mal reservoir and petroleum reservoir exploitation. Since fractures are invisible and have variable sizes from micrometers to kilometers, there is limited knowledge of their structure. We aim to deepen the understanding of fracture networks in the subsurface from their topological structures, hydraulic connectivity and characteristics at diﬀer-ent scales. We adopt the discrete fracture network method and develop an eﬃcient C++ code, HatchFrac, to make in-depth investigations possible. We start from generating stochastic fracture networks by constraining fracture geometries with dif-ferent stochastic distributions. We apply percolation theory to investigate the global connectivity of fracture networks. We ﬁnd that commonly adopted percolation pa-rameters are unsuitable for the characterization of the percolation state of complex fracture networks. We implement the concept of global eﬃciency to quantify the impact of fracture geometries on the connectivity of fracture networks. Furthermore, we constrain the fracture networks with geological data and geomechanics principles. We investigate the correlation of fracture intensities with diﬀerent dimensionality and ﬁnd that it is not feasible to obtain correct 3D intensity parameters from 1D or 2D samples. We utilize a deep-learning technique and propose a pixel-based detection algorithm to automatically interpret fractures from raw outcrop images. Interpreted fracture maps provide abundant resources to investigate fracture intensities, lengths, orientations, and generations. For large scale faults, we develop a method to generate fault segments from a rough fault trace on a seismic map. Accurate fault geome-tries have signiﬁcant impacts on damage zones and fault-related ﬂow problems. For small scale fractures, we consider the impact of fracture sealing on the percolation state of orthogonal fracture networks. We emphasize the importance of non-critically stressed and partially sealed fractures, which are usually neglected because usually they are nonconductive. However, with signiﬁcant stress perturbations, those non-critically stressed and partially sealed fractures can also contribute to the production by enlarging the stimulated reservoir volume.
|Date of Award||Nov 2020|
|Original language||English (US)|
- Physical Science and Engineering
|Supervisor||Tadeusz Patzek (Supervisor)|