Multi-scale structural analogues: rifts, segmented faults and sub-seismic scale deformation

Recent advances in digital data acquisition and visualization techniques can be used to create virtual field excursions. These excursions can help to provide new insights into classic field localities, which in turn may help to reduce geological uncertainties and to disseminate key geoscientific concepts to reservoir engineers and other non-specialists. We present THREE virtual field-excursions that examine the structural geology of passive margins, the internal structure of fault zones, and sub-seismic scale structural heterogeneity, respectively.

1). Google Earth is increasingly being used as a research tool. In particular, virtual fieldtrips created from remote sensed datasets and accessed with viewers such as Google Earth are widely used for reconnaissance studies, planning field data collection campaigns and/or providing context for virtual outcrop datasets. Our first virtual fieldtrip will utilize this tool to illustrate the geometry and spatial arrangement of normal faults on the Norwegian passive margin and the currently-active central Apennine region in Italy.

2). Faults can act as baffles to fluid flow within hydrocarbon reservoirs. The accurate prediction of structural compartmentalization in hydrocarbon reservoirs depends on realistic implementation of faults in flow simulators. Such implementation depends, in turn, upon characterizing fault zone permeability, thickness and, in some cases, internal structure (e.g. size and spatial distributions of fault rocks and sand lenses). The aim of the second virtual fieldtrip is to visit key localities along the Arkitsa, Moab and Maghlaq normal faults to examine the nature of fault segmentation, and variations in fault zone thickness and fault rock distribution.

3). Faults with throws <20 m are not visible in typical 3D seismic profiles. Consequently, there are significant uncertainties in predicting the subsurface location, geometry, and connectivity of small-scale faults and hence the impact these structures have on reservoir performance. We have addressed this problem by capturing selected outcrops using terrestrial laser scanning (TLS). The example we present is a network of sub-seismic scale, post-sedimentary faults that cut a thinly bedded sandstone/shale sequence exposed at Lamberton, SE Scotland. This virtual excursion demonstrates the power of digital datasets in quantifying fault attributes to very high levels of detail. The faults are exposed in low cliffs and on a wave-cut platform defined by three sub-horizontal sandstone beds and are characterized by small scarps (<50 cm high) that formed due to erosion of the shale interbeds. We used TLS to capture the detailed surface topography of the three sandstone beds and adjacent cliffs and to build a fault network model of the outcrop. The high spatial resolution of the Lamberton model has provided new insights into fault and relay ramp geometry within a sub-seismic scale fault network, and has allowed us to evaluate and constrain fault system attributes to a level of detail that would be difficult to achieve by traditional field studies alone.