Characteristics of fault zones in sandstones from NW England: application to fault transmissibility

Faults within outcrops of Permo-Triassic sandstones from NW England have been analysed, and their throws and fault zone thicknesses measured. These data were collected in order to provide a basis for estimating fault zone transmissibility. Logarithmic plots of fault throw versus fault zone thickness from the same localities show a positive correlation, and this relationship can be used to estimate fault zone thicknesses from fault throws derived from seismic data within similar successions. By combining fault zone thickness with laboratory-derived measurements of fault zone permeability, we show that fault transmissibilities can be estimated for input into reservoir simulation. These results can be applied to the assessment of seal potential and transmissibility in offshore oil and gas fields reservoired in Permo-Triassic sandstones. Layer thickness has a control on the fault populations, giving rise to separate population slopes for faults contained within a distinctive layer compared with those that extend outwith the layer. If layer thickness effects are not taken into account, extrapolation of a single power law trend may lead to an overestimation of the number of small faults in a population.