Bureau of Economic Geology

Fault geometry, an integrated study

October 9, 2020 9:00 AM
Anita Torabi

Dr. Anita Torabi
Professor in Structural Geology
University of Oslo, Norway

Understanding fault geometry and processes of faulting are important research areas for many applications such as petroleum exploration and production; geothermal energy managements; hydrogeology; waste disposal and CO₂ storage underground; earthquake seismology and geological hazard studies. Faults can be described as comprising a core and an enveloping damage zone (e.g. Caine et al. 1996).  The fault core accommodates most of the displacement along multiple slip surfaces and may include fault rocks such as fault gouge, cataclasites, breccia, clay smear, fractures, diagenetic features, and lenses of deformed and undeformed rocks trapped between slip surfaces. Whereas, the deformation is less intense in the damage zone and may include fractures and/or deformation bands depending on the initial porosity of the host rock, minor faults, and folds (Torabi et al., 2020). Fault geometric attributes include fault shape, fault displacement, length, damage zone width and fault core thickness (Caine et al., 1996; Torabi and Berg, 2011).

Currently, there are uncertainties in defining and understanding of fault 3D geometry. These uncertainties are to some extent related to the accessibility of the fault geometric attributes and the methodological constraints, utilizing biased data. Details of fault damage zone and fault core structures can be mapped at outcrop, however, their descriptions and statistical handling are usually constrained by their accessibility in the field and their definitions by individual researchers.

Reflection seismic data is used to study faults in the subsurface, although the interpretation of faults could be affected by the seismic resolution and the accuracy of interpretation (Marchal et al., 2003; Lohr et al., 2008; Iacopini et al., 2016; Torabi et al., 2016). Utilizing seismic attributes, we are able to directly images faults from seismic without a need for interpretation. Using this method, we extracted fault geometric attributes directly from fault images in the fault attribute volumes and studied the 3D shape and displacement distribution of faults (Torabi et al., 2019). By integrating spectral decomposition with seismic attribute workflows, we created enhanced fault attribute volumes with a high resolution, allowing us to detect, and map fault damaged zone (fault damage zone plus fault core in outcrop scale) in seismic data (Alaei and Torabi, 2017). Finally, we integrated the data from outcrop and seismic study in the scaling relations between the faults geometric attributes in order to predict the fault geometry in the subsurface.

References

Alaei, B., Torabi, A., 2017. Seismic imaging of fault damage zone and its scaling relation with displacement. Interpretation 5, 4, SP83-SP93.

Caine, J. S., Evans, J. P., and Forster, C. B. 1996. Fault zone architecture and permeability structure. Geology, 24,1025-1028.

Iacopini, D., Butler, R. W. H., Purves, S., McArdle, N. and De Freslon, N., 2016. Exploring the seismic expression of fault zones in 3D seismic volumes. Journal of Structural Geology, 89, 54–73, doi: 10.1016/j.jsg.2016.05.005.

Lohr, T., Krawczyk, C.M., Oncken, O., Tanner, D., 2008. Evolution of a fault surface fraom 3D attribute analysis and displacement measurements. Journal of Structural Geology, 30, 6, 690-700.

Marchal, D., Guirad, M., Rives, T., 2003. Geometric and morphologic evolution of normal fault planes and traces from 2D to 4D data. Journal of Structural Geology, 25, 1, 135-158.

Torabi, A., Berg, S.S., 2011. Scaling of fault attributes; a review, Marine and Petroleum Geology, 28, 8, 1444-1460.

Torabi, A., Alaei, B. and Kolyukhin, D., 2016. Analysis of fault scaling relations using fault seismic attributes. Geophysical Prospecting. doi: 10.1111/1365-2478.12440.

Torabi, A., Alaei, B., Libak, A., 2019. Normal fault 3D geometry and displacement revisited; Insights from faults in the Norwegian Barents Sea. Marine and Petroleum Geology, 99, 135-155.

Torabi, A., Ellingsen, T.S.S., Johannessen, M.U., Alaei, B., Rotevatn, A., Chiarella, D., 2020. Fault damage zone architecture and its scaling laws. From: OGILVIE, S. R., DEE, S. J., WILSON, R. W. & BAILEY, W. R. (eds) 2020.