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Mechanical stratigraphy of fractured chalks: evaluation of bias associated with fracture density through artificial fracture networks (AFN)

M. Verbiest, O. Faÿ-Gomord, C. Allanic, E. Lasseur, B. Gauthier, R. Swennen
2018 Engineering in Chalk   unpublished
Reservoir systems with both fracture and matrix porosity are labelled as dual porosity systems. The latter recently became a major topic of interest. Fracture density has major implications for chalk deposits, affecting permeability, as well as cliff and tunnel stability. This paper proposes a new methodology to evaluate fracture data from outcrops. The dataset described in this paper deals with outcrops of Santonian chalk, located in Flamborough Head (UK). This dataset was acquired based on
more » ... cquired based on manual scanlines of which the representative length was verified by Representative Elementary Length analysis. Due to the outcrop orientation and the presence of different fracture families, the dataset might be biased. For datasets dealing with strictly defined fracture families, the Terzaghi correction is often applied. However, in heterogeneous and polygonal fracture networks this correction often leads to high and erroneous fracture densities. This paper introduces Artificial Fracture Networks (AFN) to evaluate whether uncorrected data from scanlines truly underestimate fracture density of heterogeneous fracture networks. Based on the evaluation of these AFNs, it is concluded that raw scanline data are most representative for fracture spacing in heterogeneous and polygonal fracture networks. In this specific case dealing with a polygonal fracture network, it is thus best to use uncorrected scanline data to infer mechanical stratigraphy.
doi:10.1680/eiccf.64072.451 fatcat:4dpuc3an2rertd7gyrrycunhna