Many excellent aeolian sandstones suffer a decline of reservoir quality associated with structural compartmentalization by tectonic features. An onshore analogue, the Permo-Triassic Hopeman Sandstone, which crops out along the Southern side of the Moray Firth, Scotland, has been studied due to the difficulty in quantifying tectonic heterogeneities in the sub-surface. A hierarchy of structural flow barriers, with impermeable fault rock, has been observed. These vary from solitary deformation bands, via compound zones of bands to major slip surfaces/faults. Episodic faulting leads to the growth from bands to larger fault zones. Increased cementation of the sandstones is seen adjacent to these tight fault zones, and a zone of enhanced cementation, spatially governed by the main fault in the region, has been mapped. Conjugate extensional systems of deformation bands decrease in density away from major faults. Porosity reduction is related to proximity to faults, with porosity increasing abruptly away from the tectonic barrier; the deformation producing low-quality reservoir and flow barriers. Tectonic features have, intermittently, acted as both fluid conduits and barriers: enhanced cementation of sedimentary features adjacent to ‘tight’ faults shows migration of diagenetic brines along fractures. The relatively well sorted aeolian Hopeman Sandstones display better developed flow barriers than the poorly-sorted, mixed facies fluviatile Burghead Beds. Interaction of fluid-flow, diagenetic cementation and structural deformation produce flow barriers that compartmentalize the sandstones on all scales.

Large gas reserves are trapped in the coals of the Middle Jurassic (Callovian) Walloon Subgroup (lower part of the Injure Creek Group) in the Surat Basin, eastern Australia. The series is divided into the Juandah Coal Measures (upper), Tangalooma Sandstone and Taroom Coal Measures (lower).The upper and lower units are locally further subdivided. These economically important coals were deposited in an alluvial plain setting within an interior basin, which has no recorded contemporaneous marine influence. The coals are typically bituminous, perhydrous and low rank with a high volatile content. Despite individual ply (bench) thicknesses typically less than a metre, series of plies or seams of coals up to 10 m thick have historically been tentatively correlated across the entire play area (over 150 km). 2011-043r esearch-articleArticle19X10.1144/petgeo2011-043M. A. MartinWalloon Subgroup sedimentology and stratigraphy

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This paper presents a method to condition the permeability modeling of a thin, heterogeneous high-K dolomitized unit. The interval is an important drilling target for field development, so precise permeability modeling is required to optimize well placement and completion designs in order to maximize oil recovery and minimize early water breakthrough. Detailed core observations from 85 wells classify the unit into two groups: Group A, composed mainly of dolostone and Group B, comprised exclusively of calcareous dolostone. Regression analyses of plug porosity-permeability values are characterized by one regression line for each group by which dolostone represents a higher permeability trend relative to calcareous dolostone. Core-plug scaling is used to scale-up the porosity-permeability relationships from core plug- to modelscale (100 m by 100 m cells). The two regression lines accurately capture the permeability contrast within the dolomitized unit. To extend the method into a full-field model, it is necessary to calibrate the well logs to the core data. Comparison of cores with various log responses indicates the porosity log is the most useful tool to achieve this. Group A, characterized by higher dolomite content, is distinguished by a distinct decrease in the porosity due to progressive dolomitization. Porosity logs from 499 wells are interpreted and permeability values are assigned using the regression lines based on the detailed distribution map of both groups. The modeling approach using hundreds of well logs calibrated to cores yields a more detailed picture of the spatial permeability variations of the dolomitized unit. Dynamic data from ongoing history matching is also used to implicitly adjust the first-pass static model.

Tertiary to Cretaceous age karsts and collapse disturbances were observed from recent 3D seismic interpretation of an offshore Abu Dhabi oil-field. The seismic evidence of karst features was investigated using full-stack, spectral whitened, and discontinuity volumes. In addition, circular features were detected at specific sequence boundaries after examining curvature maps, disturbed amplitudes, velocity effects, and attenuation attributes. Several karsts and collapse disturbances tend to be associated with anhydrite beds overlaying thick carbonate intervals and seem to be limited to the Tertiary stratigraphic column; other karsts were observed to be limited to Cretaceous dolomite and limestone reservoir intervals. The Tertiary age karsts were observed to cause seismic image and amplitude disturbance at various depths, whereas the Cretaceous age karsts tend to be limited in radius and depth and have more limited effect on seismic response.In the attempt to better understand the limit of some karsts and collapse disturbances, well data (wireline log, conventional core, and thin-section) were investigated within the karst areas and integrated with 3D seismic data. 3D seismic based geometries and attributes were analyzed to evaluate the possibility of detecting the damage-zone limit versus velocity effect with depth due to fill material. Another effect investigated is that of fracture-fault zone distribution relative to karst localization.Analogue karst features of a similar age-range (Tertiary and younger) to the seismic examples occur within Jebel Hafit in the onshore UAE, where solution effects, debris fill, mineralization, and collapse effects can be observed and compared with the offshore examples. Here, structural discontinuities also enhance the karstic features.