Abstract: Layer-bound normal faults commonly form polygonal faults with fine-grained sediments early in their burial history. When subject to anisotropic stress conditions, these faults will be preferentially oriented. In this study we investigate how faults grow, evolve and interact within regional-scale layer-bound fault systems characterized by parallel faults. The intention is to understand the geometry and growth of faults by applying qualitative and quantitative fault analysis techniques to a 3D seismic reflection dataset from the Levant Basin, an area containing a unique layer-bound normal fault array. This analysis indicates that the faults were affected by mechanical stratigraphy, causing preferential nucleation sites of fault segments, which were later linked. Our interpretation suggests that growth of layer-bound faults at a basin scale generally follows the isolated model, accumulating length proportional to displacement and, when subject to an anisotropic regional stress field, resembling to a great extent classical tectonic normal faults.

Abstract: Normal faults grow via a sympathetic increase in their displacement and length (‘isolated model’) or by rapid establishment of their near-final length prior to significant displacement accumulation (‘constant-length model’). The isolated model has dominated the structural geology literature for >30 years, although some 3D seismic data-based studies support the constant-length model. Because they make different predictions regarding rift development, and earthquake size and recurrence intervals in areas of continental extension, it is critical to test these models with data from natural examples. Here we outline a range of techniques that constrain the kinematics of synsedimentary normal faults and thus test competing fault growth models. We then apply these techniques to three seismically imaged faults, showing that, in general, they grew in accordance with the constant-length model, although periods of relatively minor tip propagation and coeval displacement accumulation, characteristics more consistent with the isolated model, also occurred. We argue that analysis of growth strata represents the best way to test competing fault growth models; most studies utilizing this approach support the constant-length fault model, suggesting it may be more widely applicable than is currently assumed. It is plausible that the very early development of large faults is, however, characterized by the development of faults that, pre-linkage, grow in accordance with the isolated model; we may simply lack the data resolution, especially in the subsurface, to resolve this very early stage of fault growth.

Abstract This chapter describes the methodology and geologic findings of assessments of regional gas accumulations in the Greater Green River and Wind River basins that were conducted at the U.S. Department of Energy’s National Energy Technology Laboratory (DOE-NETL). These assessments were undertaken to better understand the nature and remaining potential of key elements of the nation’s natural-gas resource base. The resource assessments of DOE-NETL are unique in that they are not designed to estimate recoverability under either current or most likely future conditions. Instead, these assessments feature a detailed geologic characterization of the potential resource (a large fraction of the in-place resource) from which computer models can be used to estimate technically and economically recoverable resources for a variety of alternative future technology and market scenarios. This chapter focuses on data collected for selected parts of regional gas accumulations in the Greater Green River and Wind River basins. These results indicate the distribution of interpreted in-place resources by depth and by estimated porosity, permeability, and water saturation. Among other findings, the data confirm that a vast part of the remaining resource occurs in low-porosity formations with elevated water saturations. Also presented is an overview of the modeling results that indicates the sensitivity of resource recoverability to selected improvements in technology-related parameters.