Structure and content of the Moab Fault Zone, Utah, USA, and its implications for fault seal prediction

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 exis,ng 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.Assessment of the sealing potential or capacity of fault zones in the sub-surface is an important aspect of both the search for hydrocarbon reservoirs and their exploitation. The sealing potential of a fault is a function of the sequence juxtapositions across the fault and of the presence or absence of membrane seals resulting from the structure and content of the fault zone (Weber et al.

From mechanical modeling to seismic imaging of faults: A synthetic workflow to study the impact of faults on seismic

“…Eichhubl et al, 2005) and 3D (e.g. Childs et al, 1996;Foxford et al, 1998). However, outcrop data come mostly from faults with small-scale displacement of cm to Dm (Childs et al, 2009) and are limited to specific combinations of lithology and fault displacements (e.g.…”

“…While the internal structure of the fault core is hardly predictable (e.g. Foxford et al, 1998), the surrounding fault-related deformation decreases more or less in a systematic manner from a maximum at the centre of the fault to zero at the fault damage zone boundaries (e.g. Brogi, 2008;Schueller et al, 2013).…”

“…Much of what we know about the structure and internal properties of faults comes from outcrop studies. Field studies of exceptional fault outcrops have given unprecedented detail of the structure and properties of faults in 2D (e.g., Eichhubl et al, 2005) and 3D (e.g., Foxford et al, 1998), as well as an understanding of the physical and chemical processes operating in faults. These studies have also highlighted the complexity of faults in 3D (e.g., Childs et al, 1996, their Fig.…”

Structural heterogeneity and permeability in faulted eolian sandstone: Implications for subsurface modeling of faults

“…These may exhibit significant variability at the outcrop to oil field scale (Foxford et al, 1998;Walsh et al, 1998;Beach et al, 1999;Hesthammer and Fossen, 2000;Shipton and Cowie, 2001). The lowest permeability case, flow perpendicular to the fault zone (transverse flow), is considered for these analyses.…”

Evaluation of reservoir compartmentalization and property trends using static modelling and sequence stratigraphy

“…These fault zones are composed of disarranged and reaggregated fragments of the host rock lithostratigraphy (Foxford et al 1998;Aydin and Eyal 2002). The total flow retarding effect of a fault is caused by the distribution, rearrangement, and juxtapositions of lithological fragments, and thus, permeability collapses within faulted rocks.…”