An Integrated Approach to Incorporate Intraplate Stress, Lithospheric Memory and Slip Tendency Into Models for Fault Zone Permeability

Worum, G.¹, J.D. Van Wees², A. Gartrell³, F. Mulders², S.A.P.L. Cloetingh⁴ (1) Eotvos University, Budapest, Hungary (2) TNO, Utrecht, Netherlands (3) CSIRO, Bentley, Australia (4) Free University, Amsterdam (Vrije Universiteit), Amsterdam, Netherlands

In the past decade, a variety of methodologies have been developed for the characteri­zation of fault zone permeability. Analysis techniques estimate fault permeability parameters from Shale Gauge Ratio (SGR) and fault zone thickness. However, as recently shown for the Timor Sea, SGR based fault transmissibility fails to explain leakage. Here, a new fill-spill model has been produced for the Skua Oil Field that challenges the importance of Mio-Pliocene fault reactivation as the principal control on trap integrity. Integration of contempo­rary and palaeo-fluid-flow indicators within a 3D structural framework, guided by 3D struc­tural restoration, highlighted the important role of pre-existing fault intersections. The Timor Sea case demonstrated that fault reactivation can act as the principal control on fault per­meability through the formation and opening of fractures in the fault zone.

Based on the insights from this case study we developed an integrative model for qual­ititatively assessing formation and opening of fractures, which take as input parameters: (1) evolution of the stress field, (2) fault slip tendency and fault displacement and (3) fault size, shape and linkage. It is demonstrated that the integration of these factors can easily be incorporated in the standard workflow of building 3D geological models for exploration and production. Predicted fault fracture density magnitudes are qualitative and subject to many uncertainties, which will be discussed. Of particular importance is knowledge on the stress history and lithospheric memory (e.g. pre-existing fault size), making particular fault zones more prone to fault reactivation and fault fracturization than others.