Speaker
Description
Despite the amount of research on flow and transport in single fractures and fracture networks, there is a gap in knowledge between the field data describing natural fractures and the models that represent them. Natural fracture networks exhibit ranges of fracture lengths, connectivity, and aperture distributions, which directly affect the flow and transport behavior within the network. The values for these parameters are related to the formation conditions for the fractures themselves, whether from mechanical, chemical, or thermal processes, or some combination thereof. In numerical models of fracture networks, values for these parameters are commonly assumed based on statistical distributions or are stochastically generated. This is typically done under the guise of theoretical considerations, meaning the actual values are secondary to the phenomenology and quantities of interest under study. However, some field data indicate that apertures do not follow well-defined statistical distributions, particularly in sedimentary rocks that have undergone diagenesis. If certain fractures are cemented in the network, the flow and transport behavior can be expected to vary because connectivity can be reduced. Incorporating such effects into numerical models has only been done for simple cases in three-dimensions and the effects of such aperture changes have not been systematically investigated or linked to other fracture network characteristics or high-fidelity flow and transport simulations. Therefore, it is critical to understand when typical modeling assumptions might fail to accurately predict flow and transport in natural or engineered fractured systems. In this work, we investigate how model assumptions that neglect rock specific aperture data might impact flow and transport through fracture networks. Specifically, we have incorporated the concept of the emergent threshold, or the characteristic length scale above which fractures will flow, into discrete fracture network models and performed high fidelity flow and transport simulations based on both field and stochastically generated aperture and fracture length data. Changes in emergent threshold can alter the flow structures within the networks by closing existing preferential pathways and lowering effective permeabilities, which in turn can increase flow channeling in the networks, but these effects are closely linked to the underlying network structure (i.e., topology) and density, as well as the matrix permeability. Our results indicate that emergent threshold/fracture sealing can be a first order control on network scale flow and transport and further motivates future work linking additional field observations to numerical models of fracture networks.
| Country | United States |
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