TY - JOUR
T1 - Impact of mechanical heterogeneity on joint density in a welded ignimbrite
AU - Soden, A.M.
AU - Lunn, R.J.
AU - Shipton, Z.K.
PY - 2016/8/31
Y1 - 2016/8/31
N2 - Joints are conduits for groundwater, hydrocarbons and hydrothermal fluids. Robust fluid flow models rely on accurate characterisation of joint networks, in particular joint density. It is generally assumed that the predominant factor controlling joint density in layered stratigraphy is the thickness of the mechanical layer where the joints occur. Mechanical heterogeneity within the layer is considered a lesser influence on joint formation. We analysed the frequency and distribution of joints within a single 12-m thick ignimbrite layer to identify the controls on joint geometry and distribution. The observed joint distribution is not related to the thickness of the ignimbrite layer. Rather, joint initiation, propagation and termination are controlled by the shape, spatial distribution and mechanical properties of fiamme, which are present within the ignimbrite. The observations and analysis presented here demonstrate that models of joint distribution, particularly in thicker layers, that do not fully account for mechanical heterogeneity are likely to underestimate joint density, the spatial variability of joint distribution and the complex joint geometries that result. Consequently, we recommend that characterisation of a layer’s compositional and material properties improves predictions of subsurface joint density in rock layers that are mechanically heterogeneous.
AB - Joints are conduits for groundwater, hydrocarbons and hydrothermal fluids. Robust fluid flow models rely on accurate characterisation of joint networks, in particular joint density. It is generally assumed that the predominant factor controlling joint density in layered stratigraphy is the thickness of the mechanical layer where the joints occur. Mechanical heterogeneity within the layer is considered a lesser influence on joint formation. We analysed the frequency and distribution of joints within a single 12-m thick ignimbrite layer to identify the controls on joint geometry and distribution. The observed joint distribution is not related to the thickness of the ignimbrite layer. Rather, joint initiation, propagation and termination are controlled by the shape, spatial distribution and mechanical properties of fiamme, which are present within the ignimbrite. The observations and analysis presented here demonstrate that models of joint distribution, particularly in thicker layers, that do not fully account for mechanical heterogeneity are likely to underestimate joint density, the spatial variability of joint distribution and the complex joint geometries that result. Consequently, we recommend that characterisation of a layer’s compositional and material properties improves predictions of subsurface joint density in rock layers that are mechanically heterogeneous.
KW - joint density
KW - joint distribution
KW - material properties
KW - mechanical heterogeneity
KW - mechanical layer thickness
UR - https://www.sciencedirect.com/journal/journal-of-structural-geology
U2 - 10.1016/j.jsg.2016.05.010
DO - 10.1016/j.jsg.2016.05.010
M3 - Article
AN - SCOPUS:84973645175
SN - 0191-8141
VL - 89
SP - 118
EP - 129
JO - Journal of Structural Geology
JF - Journal of Structural Geology
ER -