Faults in nature commonly affect surrounding rock volumes and can as such be described as fault envelopes with a given internal geometry and architecture. Modeling techniques currently employed when modeling faults in petroleum reservoirs are mostly two-dimensional (2-D); hence, a need is present for more accurate and realistic description and quantification of deformational architectures and properties to accurately predict fluid flow in fault zones.Fault facies (FF) modeling is a concept for three-dimensional (3-D) fault zone characterization, facies modeling of fault rocks and fluid flow simulation, which is presented here and demonstrated by the use of a synthetic fault model. FF modeling is performed by first generating a 3-D grid of the fault envelope, which includes the conventional fault plane. Second, a kinematic strain calculation is executed in the FF grid. The strain parameter is used to calculate a fault product distribution factor (FPDF), which describes the fault displacement in the fault envelope. This parameter together with strain distribution is subsequently used to condition the fault model for facies modeling. Finally, FF modeling is executed. To achieve adequate flexibility and realism, pixel-based modeling is combined with object-based modeling methods to populate the FF grid with facies.This synthetic model shows that it is possible to honor structural outcrop observations in fault zones, and FF modeling is able to produce realistic looking fault zone deformation structures in 3-D. It is possible to implement faults with varying width and displacement, although the FF grid itself has a regular fixed width. This is highly advantageous as compared to controlling the fault geometry with the grid itself. We propose that FF modeling can improve fault zone characterization and also capture fluid flow uncertainty in fault zones in a more realistic way than is possible with 2-D methods.

for the fourteenth SPE Bergen One Day seminar 18th April 2007 Session: Geoscience and reservoir engineering Faults in reservoir models – unwanted surprises and new methods for avoiding them Tveranger, J.*, Braathen, A.**, Cardozo, N.*, Espedal, M.*, Fredman, N.*, Fossen, H.**, Nøttveit, H.*, Røe, P.***, Skorstad, A.***, Soleng, H.*** and Syversveen, A-R.*** * Center for Intergrated Petroleum Research (CIPR), University of Bergen, Allègaten 41, N-5007 Bergen, Norway ** The University Centre in Svalbard, P.O. Box 156, N-9171 Longyearbyen , Norway *** The Norwegian Computing Centre, Gaustadallèen 23 P.O. box 114, Blindern N-0214 Oslo, Norway Standard reservoir modelling techniques routinely incorporate faults as simple offsets along grid splits. The impact of faults on reservoir fluid flow is thereby captured by the combined effect of stratigraphic displacement and transmissibility modifiers attached to the cell surfaces bordering the grid split. These transmissibility modifiers can be derived either from specialised tools calculating expected transmissibility from combining information on reservoir lithology with fault throw, or by ad hoc history matching of the simulation model. However, this approach disregards the fact that fault impact in reservoirs is commonly not limited to a single, clear-cut fault plane but affects a volume of host rock thereby creating a complex 3D architecture. By failing to incorporate the presence of often extensive fault damage zones and fault core architectures into the reservoir model actual 3D flow inside and through fault zones is not captured in-place volumes are overestimated fault sealing (including capillary seals) is highly simplified communication along faults can not be forecast model uncertainty cannot be properly evaluated as fault features critical for reservoir behaviour are not included in the model hazardous areas for drilling can not be reliably predicted The Fault Facies project addresses this problem by a concerted research effort involving structural geologists, mathematicians, modellers, programmers and reservoir engineers. The project has developed a practical methodology that allows volumetric gridding of fault zones on reservoir scale models and populating the resulting fault envelopes with realistic fault architectural elements and petrophysical properties. Models are built using a standard reservoir modelling tool (Irap RMS) employing a customised gridding algorithm in HAVANA. Architecture and petrophysical properties of the fault zones are modelled by adapting facies model tools developed for object based modelling of sedimentary facies and employing volumetric strain as a conditioning parameter for the resulting fault zone architecture and petrophysical properties. The new method is fully integrated with existing modelling workflows and can be added onto existing models with no need to build new models from scratch. Although still under development the Fault Facies method offers a practical solution to evaluation of fault impact on reservoir fluid flow in realistic detail.