In order to calibrate equations for fault seal capacities to a specific basin, faults were analysed using core material from several Neogene hydrocarbon fields in the Vienna Basin, Austria. All studied specimens are siliciclastic rocks that were sampled from a depth interval < 2000 m, share a similar depth at time of faulting, diagenetic conditions and maximum burial depth. Laboratory results showed a permeability reduction in all fault rocks compared to the host rocks. Both, the highest and the lowest fault seal capacities were observed in the same fault rock type with a low phyllosilicate and clay content, classifying as cataclastic deformation bands. Investigating the strong permeability variations within these fault rocks, microscopic analyses revealed that the fault seal potential is strongly linked to the detrital dolomite content in the host rock. Grain size reduction processes occur preferably in the dolomite grains, accompanied by cementation. Our study suggests that – in addition to using standard fault seal analysis algorithms – accounting for host rock composition and grain size reduction therein might help to further constrain fault seal behaviour in shallow depths. Fault seal mechanisms need to be understood on field, formation and microscale before drawing conclusions for a full basin calibration.

Thematic collection: This article is part of the Fault and top seals collection available at: https://www.lyellcollection.org/cc/fault-and-top-seals-2019

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