Abstract - The structure and content of the Moab Fault zone
are described for 37 transects across the fault zone where throws range
from less than 100m to c. 960m. The 45km long fault trace intersects a
sedimentary sequence containing a high proportion of sandstones with good
reservoir properties, interspersed with numerous mudstone layers. Typically,
the fault zone is bounded by two external slip zones with the fault zone
components separated by up to nine internal slip zones. Fault zone components
are tabular lenses of variably deformed sandstones and sandstone cataclasites
and breccia, with a wide size range, usually enclosed in a matrix of shaley
fault gouge containing mm to m scale entrained sandstone fragments. Neither
fault zone structure nor content can be predicted by extrapolation over
distances as little as 10m. Although variable in thickness, shaley gouge
is always present except where the mudstone is < c. 20% of the faulted
sequence. The distribution of shaley gouge conforms with existing algorithms
for predicting the presence or absence of shaley gouge in subsurface fault
zones. The fault zone heterogeneity is attributed to tip-line and asperity
bifurcation processes.
In: Faulting, Fault Sealing and Fluid Flow in Hydrocarbon
Reservoirs. Geological Society of London, Special Publication, 147, 87-103, 1998.