Paper No. 13
Presentation Time: 11:40 AM


VROLIJK, Peter1, MYERS, Rodrick2, KETTERMANN, Michael3, KLEINE VENNEKATE, Gisa4, NOLLET, Sofie5, NOORSALEHI-GARAKANI, Sohrab3, SCHMATZ, Joyce6 and URAI, Janos L.7, (1)N/a, ExxonMobil Upstream Research Co, P. O. Box 2189, Houston, TX 77252-2189, (2)ExxonMobil Upstream Research Co, P. O. Box 2189, Houston, TX 77252-2189, (3)Geologie-Endogene Dynamik, RWTH-Aachen, Lochnerstr 4-20, Aachen, 52056, Germany, (4)Geotechnik im Bauwesen, Institut fuer Grundbau, Bodenmechanik, Felsmechanik, u. Verkehrswasserbau, Mies-van-der-Rohe-Str. 1, Aachen, 52074, Germany, (5)Petrel Exploration Geology - Product Analyst, Schlumberger Information Solutions, Ritterstr. 23, Aachen, 52072, Germany, (6)Lehrgebiet für Geologie-Endogene Dynamik, RWTH Aachen, Lochnerstrasse 4-20, Aachen, 52056, Germany, (7)Structural Geology, Tectonics and Geomechanics, RWTH Aachen, Lochnerstrasse 4-20, Aachen, 52056, Germany,

Normal faults in under- to normally consolidated sedimentary rocks are a complex assortment of the offset lithologies. Our conceptual model of a fault zone includes variably deformed sedimentary slivers (negligible to moderate shear strain) separated by localized shear zones. In this view the gross hydrologic properties of a fault zone depend on the lithologies included in the fault and the geometric distribution and continuity of those lithologies.

Available methodologies used to evaluate cross-fault flow properties (e.g., SGR or CSP) are predicated on the definition of a fault as a single surface as defined by seismic reflection data and do a poor job of accounting for the variability in fault zone structure observed in nature. Over the past decade we have undertaken a series of novel sandbox experiments to define primary controls on fault zone structure that determine cross-fault flow in simple sand-clay systems. We have observed how ‘soft’ clays become volumetrically concentrated in fault zones, how ‘hard’ clays bend, break, and sometimes shear-soften, and how multiple clay beds become amalgamated and form significant cross-fault barriers. We have also discovered that holes develop in the gouge that overcome the permeability-reducing effects of the clay smear and that these holes may be associated with the intricate relay structure of the fault zone. Moreover, the type of fault relay complexity may be associated with the boundary condition of fault propagation dip with respect to the material properties of the faulted materials (i.e. friction angle).

Taking these experiments in the context of other field and subsurface examples, we have learned that fault processes that deform the offset and entrained sedimentary lithologies play an important role in determining the hydrologic properties of faults as they determine the distribution and continuity of those lithologies, and counteracting those processes are those that thin and create holes in fault gouge lithologies.