Abstract We examined the distribution of fault rock and damage zone structures in sandstone and shale along the Moab fault, a basin-scale normal fault with nearly 1 km (0.62 mi) of throw, in southeast Utah. We find that fault rock and damage zone structures vary along strike and dip. Variations are related to changes in fault geometry, faulted slip, lithology, and the mechanism of faulting. In sandstone, we differentiated two structural assemblages: (1) deformation bands, zones of deformation bands, and polished slip surfaces and (2) joints, sheared joints, and breccia. These structural assemblages result from the deformation band-based mechanism and the joint-based mechanism, respectively. Along the Moab fault, where both types of structures are present, joint-based deformation is always younger. Where shale is juxtaposed against the fault, a third faulting mechanism, smearing of shale by ductile deformation and associated shale fault rocks, occurs. Based on the knowledge of these three mechanisms, we projected the distribution of their structural products in three dimensions along idealized fault surfaces and evaluated the potential effect on fluid and hydrocarbon flow. We contend that these mechanisms could be used to facilitate predictions of fault and damage zone structures and their permeability from limited data sets.

Abstract Faults are important elements of petroleum systems that influence the migration and trapping of hydrocarbons in sedimentary basins. When faults undergo displacement, their fluid transmissibility properties change as a result of juxtaposing lithologies across the fault, by smearing semi-permeable or impermeable argillaceous rocks within fault zones and by pumping or valving aqueous fluids. We describe here a 4D hydrocarbon migration model that incorporates juxtaposition and argillaceous smear processes. The technique uses the geometries of strata that are cut by faults and their physical properties to construct 3D models in which the evolution of cross-fault relationships can be calculated and the development of fault-zone argillaceous smear predicted. Hydrocarbon migration pathways through faulted structures are then investigated with a 4D migration model based on invasion percolation (IP) techniques. The controls on hydrocarbon migration have been investigated for fieldwork-derived models of rock volumes from the Moab Fault, Utah, USA to test the modelling techniques against reality. As a result predominantly of argillaceous smear, hydrocarbons are shown to accumulate in the hanging wall of parts of the modelled section of the Moab Fault, but leak across juxtaposed sandstones elsewhere on the fault to produce footwall accumulations. The techniques are then applied to a seismically derived model of the Artemis Field, UK Southern North Sea, to demonstrate how hydrocarbon charging history and pathways are influenced by fault geometries. Multiple model realizations enable the risk associated with charging of individual fault compartments to be assessed.

Abstract Structural geometries, faults and their movement histories, together with the petrophysical properties of flow units, are some of the major controls on hydrocarbon migration pathways within sedimentary basins. Currently, structural restoration, fault-seal analysis and hydrocarbon migration are treated as separate approaches to investigating basin geohistory and petroleum systems. Each of these separate modelling approaches in their own fields is advanced and sophisticated but they are not compatible with each other. Lack of integration produces incorrect palaeogeometries in basin models and inaccurate migration pathways. A combined structural restoration and fault-seal analysis technique, integrated with fast hydrocarbon migration pathway modelling code based on invasion percolation (IP) methods, is described. These modelling methods are used to develop a 4D basin modelling workflow in which evolving basin geohistories and geometries form an integral part of the analysis of hydrocarbon migration and trapping. By combining structural restoration and 3D fault-seal analysis it is possible to investigate the evolution of structurally complex traps through time. Integration of these techniques with a numerically fast migration pathway modelling technique allows hydrocarbon migration pathways and accumulations to be modelled through the evolution of the basin with time. Additionally, the effects of uncertainties in structural geometry, fault seal or any of the model input parameters can be explored using a risk-driven approach to modelling. These methods are demonstrated using synthetic, computer generated, 3D models and a well-constrained model of the Moab Fault, Utah, USA. Comparison of modelled structural geometries, fault-seal properties and predicted trapped hydrocarbons with outcrop data is used to validate the integrated modelling approach. The validated techniques are then applied to a seismically derived, 3D model from the southern North Sea, UK, to demonstrate how an integrated, risk-driven approach to modelling allows the effects of uncertainties in the distribution of hydrocarbon accumulations to be investigated.

Abstract The geometry, orientation and distribution of deformation bands and fractures in eolian sandstones, siltstones and shales of the San Rafael Desert and Moab Fault area have been investigated. The results show that deformation bands, which are cataclastic in eolian sandstones and disaggregation structures in siltstones, are unevenly distributed throughout the damage zone in the form of individual bands, deformation band zones and deformation band clusters. The density of bands increases with increasing grain size. In thin (<3 m) eolian sandstones deformation band frequency is significantly lower than in thicker eolian sandstones, whereas above this thickness the frequency seems not to be related to layer thickness. Furthermore, large faults do not develop higher concentrations of deformation bands. Somewhat simplified, this suggests that damage zone growth occurs by expansion into its hanging wall and footwall. Still, the highest concentrations of deformation bands occur close to the main fault, which is of importance when considering their effect on fluid flow. Their general fault-parallel conjugate arrangements favour intra-damage zone flow parallel to rather than perpendicular to the fault.