ALBERT

Description: Recent technological advances have made the collection of digital geological data from outcrops a realistic and efficient proposition. The world-class exposures of Permian basin-floor turbidite fans of the Tanqua depocentre, Karoo Basin, South Africa have been the focus of one such study. These outcrops are faulted at a subseismic scale (displacements of up to 40 m), with continuous exposures of up to 40 km in depositional dip and 20 km strike directions. Digital data collection has been undertaken using a variety of methods: differential global-positioning systems (DGPS) mapping, surveying using laser total station and laser rangefinders, ground- and helicopter-based digital photography and photogrammetry, and digital sedimentary outcrop logging as well as geophysical data from boreholes. These data have then been integrated into several 3-D geological models of the study area, built using a subsurface reservoir-modelling system. The integrated dataset provides insights into the stratigraphic evolution of a deep-water fan complex by allowing true 3-D analysis and interpretation of data collected in the field. The improved understanding of these deep-water fan systems will improve existing models of offshore analogues by enhancing understanding of geometries and trends not resolvable from existing offshore data and by identifying potential problematic areas for fluid flow. Initial results from the application of this approach have been successfully applied to the conditioning of stochastic geological models of a subsurface deep-water reservoir from the North Sea.

Description: The routine application of digital survey technologies such as terrestrial lidar and photogrammetry to the characterization of fault and fractures in outcrop over the past decade has resulted in major advances in terms of the efficiency of discontinuity data acquisition. However, the reliance upon mesh- and point-cloud–based analysis approaches means that data sets obtained from these sources commonly offer heavily abstracted views of the measured fracture network due to the limited resolution of the input model. Here, we present an alternative approach that combines conventional two-dimensional (2D) image analysis with ray-tracing techniques to extract three-dimensional (3D) fracture trace maps from photogrammetrically calibrated image sequences. These 3D trace objects may be interrogated to obtain fracture network properties (trace length, intensity, and connectivity), with probabilistic methods used to estimate fracture orientation for high collinearity traces. Our approach possesses a number of advantages over existing digital surface reconstruction-based methods, with the use of a 2D pixel-based approach allowing established image-processing routines (e.g., edge detection/connected components analysis) to be applied to the characterization of fracture and fault properties. Moreover, the innately high resolution of the input images results in practically lossless 3D fracture trace representation, limiting truncation effects. As a result, the method is capable of resolving local variability in higher-order fracture properties such as fracture intensity, which are difficult to derive using existing approaches. We demonstrate the approach on pervasively faulted Permian age exposures of the Vale of Eden Basin, UK.

Description: 〈span〉Outcrop analogue studies allow detailed investigation of sandstone body geometry and architecture within fluvial systems. Characterization of these ele­ments is fundamental to understanding and quantifying sandstone body connectivity within hydrocarbon reservoir models, and hence improving recovery from those reservoirs being modeled. This study utilized a laterally and vertically continuous terrestrial light detection and ranging (lidar) data set from the La Serrata section of the Oligocene–Miocene Huesca fluvial fan, in the Ebro Basin in Spain. This data set was used to create a high-resolution three-dimen­sional digital outcrop model of a 2 km〈sup〉2〈/sup〉 cliff section representing the heterogeneity in the medial (midfan) portion of a large fluvial fan. Geostatistical information (i.e., sandstone body width and thickness) extracted from the models using quantitative analytical techniques, integrated with traditional sedimentary log data, allowed the calculation of probability density functions of 42 sandstone bodies from corrected (true) width measurements. These data show that sandstone bodies are up to 6 m thicker and 209 m wider than previous studies have estimated. Furthermore, an observed temporal trend of thickening and widening of sandstone bodies up section before a reduction in the uppermost portion provides evidence for possible avulsion events. These data, compared with previous studies of this and other fluvial systems, illustrate the efficacy of digital outcrop models as quantitative tools for accurate characterization of critical reservoir elements from outcrop analogues.〈/span〉

Description: Recent developments in workflows and techniques for the integration and analysis of terrestrial LiDAR (Light Detection And Ranging) and conventional outcrop datasets are demonstrated through three case studies. The first study shows the power of three-dimensional (3D) data visualization, in association with an innovative surface-modelling technique, for establishing large-scale 3D stratigraphical frameworks. The second presents an approach to derive reliable geometrical data on sediment-body geometries, whereas the third presents a new technique to quantify the proportions, distributions and variability of sedimentary facies directly from outcrop. In combination, these techniques provide essential conditioning data for geocellular and stochastic facies modelling. Built upon robust, reproducible and quantitative data, the resultant models combine realistic 3D geological architectures with sufficient quantities of reliable numerical data required for stable statistical analysis and establishing uncertainty. Together this new information provides detailed understanding and quantification of the 3D complexity of the sedimentary systems in question, thus offering insights of value for predicting the subsurface anatomy of analogous petroleum systems. As such, use of LiDAR, when combined with conventional field geology, offers a powerful tool for quantitative outcrop analysis, tightly constraining 3D structural and stratigraphical interpretations, and effectively increasing the statistical significance of outcrop analogues for reservoir characterization.

Description: 〈span〉〈div〉Abstract〈/div〉Outcrop analogue studies allow detailed investigation of sandstone body geometry and architecture within fluvial systems. Characterization of these elements is fundamental to understanding and quantifying sandstone body connectivity within hydrocarbon reservoir models, and hence improving recovery from those reservoirs being modeled. This study utilized a laterally and vertically continuous terrestrial light detection and ranging (lidar) data set from the La Serrata section of the Oligocene–Miocene Huesca fluvial fan, in the Ebro Basin in Spain. This data set was used to create a high-resolution three-dimensional digital outcrop model of a 2 km〈sup〉2〈/sup〉 cliff section representing the heterogeneity in the medial (midfan) portion of a large fluvial fan. Geostatistical information (i.e., sandstone body width and thickness) extracted from the models using quantitative analytical techniques, integrated with traditional sedimentary log data, allowed the calculation of probability density functions of 42 sandstone bodies from corrected (true) width measurements. These data show that sandstone bodies are up to 6 m thicker and 209 m wider than previous studies have estimated. Furthermore, an observed temporal trend of thickening and widening of sandstone bodies up section before a reduction in the uppermost portion provides evidence for possible avulsion events. These data, compared with previous studies of this and other fluvial systems, illustrate the efficacy of digital outcrop models as quantitative tools for accurate characterization of critical reservoir elements from outcrop analogues.〈/span〉

Description: New, high-resolution lithofacies data from hanging-wall Miocene synrift (Rudeis Formation) exposures of the eastern Suez Rift margin, Egypt, reveal a submarine slope depositional system dominated by coarse-grained (pebble), heterogeneous, lenticular beds, formed by coalescing turbidity currents, slumps, and debris flows deposited on deforming submarine substrate. Flows include prerift clasts and contemporaneous shallow-marine fossil fragments originating from an uplifted eastern hinterland. Multiple terrestrial drainages debouched onto faulted offshore slopes or fed small fan deltas on narrow shelves (〈0.5 km width). Steep, subaerial rift-flank topography also shed rock avalanche and landslide material offshore. The 〉360 m Rudeis Formation is divided into stratigraphic units R1 and R2, which exhibit upward-coarsening and unordered vertical motifs. Ongoing faulting influenced synrift deposition by controlling the locus of subsidence and gravity base level. Mesoscale faults became inactive during Rudeis Formation times, with strain localized on the large rift border fault system, leading to a wider basin with time. We compare 16 subaqueous rift-margin basin fills from various tectonic and geographic settings and show they generally represent proximal gravity-flow deposits dominated by nongraded beds. We find little commonality in vertical grain-size trends, highlighting the diversity of stratal architectures. Most basin fills show an inverse relationship between maximum clast size and shelf width. We propose a new model to capture the spectrum of sedimentary responses to rifting within rift-margin basins, varying as a function of shelf width, slope gradient, maximum grain size, and textural maturity. Rudeis Formation strata at north Wadi Baba represent a particularly coarse-grained end member, deposited on steep slopes, with a narrow shelf.