Abstract It is well established that compaction bands (CBs), joints and faults are often present in the same rock volume in the Jurassic aeolian Aztec Sandstone, exposed in the Valley of Fire State Park, Nevada, USA. Because the permeability of CBs can be one or more orders of magnitude less than the matrix permeability, and joint permeability, depending on its aperture, can be several orders of magnitude greater than matrix permeability, the combined effect of these structures on subsurface flow can be complex and substantial. In this study, we investigate the effects of a variety of intersecting geological structures on fluid flow. This is accomplished by performing two- (2D) and three-dimensional (3D) permeability upscaling and waterflood simulations over areas/volumes populated by hydraulically interacting geological features. The regions considered are approximately the size of typical grid blocks used for reservoir or aquifer flow simulations, so the results are of practical interest. The systems studied include models with two sets of vertical CBs intersecting at various angles, an inclined CB set intersecting a vertical CB set, a joint set intersecting a CB set at various angles, and a small fault and its damage zone overprinting a CB set. Our numerical results quantify the impact of these composite structures on subsurface flow and show, for example, that the intersection angle of two sets of structures can have a considerable effect on the upscaled directional permeability. In addition, waterflood simulations demonstrate that the efficiency of oil recovery can be significantly impacted by the direction of flow relative to the orientation of intersecting geological structures.

Abstract Using an elastic dislocation model, we incorporate a historical earthquake catalog, mapped Marmara Sea fault traces, and fault slip distributions for the 1999 Izmit earthquake inferred from InSAR and GPS data to determine various stress change scenarios crucial for evaluating future earthquake potential in the eastern Marmara Sea. We have tested six plausible past rupture configurations arising from the uncertainty in the location of the western termination of 1999 Izmit earthquake rupture and the location of the 1963 Yalova earthquake rupture. Coulomb stresses calculated are increased on the Princes’ Islands, Çinarcik, and Armutlu fault segments in each case. In four of the six plausible configurations of previous ruptures, the Çinarcik fault receives the greatest average stress change. In one other configuration, the average stress increase on the Princes’ Islands fault is greatest. In another, the stress changes on the Çinarcik and Princes’ Islands faults are comparable. Moreover, we show that rupture initiating on either the Princes’ Islands or Armutlu faults would be favoured to propagate onto the Central Marmara, or Imrali fault, respectively, based on the favourable geometries of the respective fault intersections. Rupture initiating on the Çinarcik fault, however would be limited to a much shorter length based on its mapped western termination. Therefore, while the earthquake-induced stress changes may, in most cases, be greatest on the Çinarcik fault, an earthquake initiating on this fault segment may produce a shorter cumulative rupture compared to rupture initiated on the two other major eastern Marmara Sea fault segments. These results are encouraging for the use of geomechanical modelling tools in addressing uncertainties inherent in most geological and geophysical data applied to earthquake-related problems.

Abstract To refine flow models for sand-dominated fault rock, we present petrophysical data of host and fault rock samples from the eolian Aztec Sandstone, Valley of Fire State Park, Nevada, that has been deformed by strike-slip faults formed by progressive shearing along joint zones. The data include bulk mineralogy, porosity, permeability, grain-size distribution, and mercury-injection capillary pressure measurements of 40 host, fragmented, and fault rock samples. To investigate the impact of shear strain on fault zone properties, three sample localities with average shear strains of 28, 63, and 80 were investigated (25-160-m [82-525-ft] slip). No bulk mineralogical changes caused by fault zone cementation or mineral alteration were detected when comparing host and fault rock. Fault rock permeability is one to three orders of magnitude lower than median host rock permeability. Porosity reductions are less pronounced and show considerable overlap in values between the sample suites. Some fault rock samples appear to have dilated with respect to median host rock porosity. Median grain sizes for fault rock samples range from 3 to 51 mm, which is as much as two orders of magnitude reduction from host rock median grain sizes. There appears to be a lower limit of median grain size of 3 mm for fault rock samples irrespective of average fault shear strain. Fault rock capillary injection pressures range from one to almost two orders of magnitude higher than the host rock equivalent. For standard fluid properties, calculated maximum sealable hydrocarbon column heights range between 10 and 70 m (33 and 230 ft) of gas and 20-120 m (66-400 ft) of oil. These petrophysical data show that faults formed by shearing of joints in high-permeability, sand-prone systems will act as significant barriers to fluid flow during reservoir production and might be capable of sealing small to moderate hydrocarbon columns on an exploration timescale as well, assuming adequate continuity of the fault rock over large areas of the fault.