Anthony Robin Westerman

3D high-resolution digital models of outcrop analogue study sites to constrain reservoir model uncertainty: an example from Alport Castles, Derbyshire, UK

Advances in data capture and computer technology have made possible the collection of 3D high-resolution surface and subsurface digital geological data from outcrop analogues. This paper describes research to obtain the 3D distribution and internal sedimentary architecture of turbidite channels and associated sediments at a study site in the Peak District National Park, Derbyshire, UK. The 1D, 2D and 3D digital datasets included Total Station survey, terrestrial photogrammetry and remote sensing, sedimentary logs and a Ground Penetrating Radar (GPR) dataset. A grid of 2D GPR profiles was acquired behind a cliff outcrop; electromagnetic reflection events correlated with cliff face sedimentary horizons logged by Vertical Radar Profiling. All data were combined into a Digital Solid Model (DSM) dataset of the site within reservoir modelling software. The DSM was analysed to extract 3D architectural geometries for petroleum reservoir models. A deterministic base model was created using all information, along with a suite of heterogeneous turbidite reservoir models, using 1D, 2D or 3D information. The model suite shows significant variation from the deterministic model. Models built from 2D information underestimated connectivity and the continuity of geobodies, but overestimated channel sinuosity. Advantages of using 3D digital outcrop analogue data for 3D reservoir models are detailed.

Sand Volcanoes of the Carboniferous Ross Formation, County Clare, Western Ireland: 3-D Internal Sedimentary Structure and Formation

An exceptionally well preserved sand volcano cluster approximately 7 m (23 ft) in diameter lies on top of mass-wasting deposits in the Carboniferous Ross Formation in western Ireland. Sandstone dikes were observed near the volcanoes, emanating from sandstone units beneath the slumped intervals. The volcano cluster was the focus of sedimentary, geophysical (ground-penetrating radar), and surveying (differential global positioning system) methods, with the aim of digitally reconstructing the volcanoes in three dimensions and elucidating their origin and significance. Data analysis determined that single volcanoes were, in fact, composite, with early small cones being overwhelmed by a later dominant cone during deposition. Volcanoes were sourced through feeder dikes that were correlated through slump horizons to underlying in-situ sandstones. A four-stage origin is inferred: (1) initial overpressured sand escaped up through tension gashes in the slump horizons to deposit multiple, small sand cones on the new sea floor; (2) more widely spaced vents allowed multiphase ejection to envelop initial cones and to produce larger volcanoes with a single vent; (3) composite volcanoes loaded and subsided into the underlying substrate and local sand chamber during continued deposition before final cessation; and (4) deposition of overlying pelagic sediments and lithification. Volcanoes may be sited on local sea-floor, topographic highs.

The use of vertical radar profiling (VRP) in GPR surveys of ancient sedimentary strata

Abstract Vertical radar profiling (VRP) is an application of ground penetrating radar (GPR) technologies that can extract important subsurface information from suitable outcrops. Using standard GPR equipment, a site-specific time-depth calibration can be obtained, along with correlation of observed sedimentological horizons exposed on cliff-faces. These horizons may then be correlated with subsurface reflection events imaged on fixed-offset profiles. Summaries of six GPR study sites, where the VRP technique was used, are detailed. Where possible, CMP and VRP velocities have been compared, and show good correlations. Geochemical analysis of selected sedimentary rocks shows that increasing grain size and quartz mineral percentages generally lead to increased GPR velocities. Reflection events tend to be associated with sandstone/shale boundaries.

The use of GPR to image three-dimensional (3-D) turbidite channel architecture in the Carboniferous Ross Formation, County Clare, Western Ireland

Abstract Petroleum reservoir models are currently built from two-dimensional (2-D) information. An understanding of both the large-scale and internal three-dimensional (3-D) architecture of turbidite channel deposits is important for both hydrocarbon exploration and production. A ground penetrating radar (GPR) survey was undertaken on a study site exposing Upper Carboniferous Ross Formation deposits in western Ireland. Both channel margins and intrachannel fill were imaged in 3-D. Constant-offset, 2-D reflection sections were calibrated by vertical radar profiles. GPR data were integrated with sedimentary and survey data to produce a 3-D model of the study site.

Reservoir Impact of Small-scale Aeolian Dune Architecture - From Acquisition to Simulation in the Wahiba Sands, Oman

Small-scale dune heterogeneity has a significant impact upon recoverable reserves within aeolian hydrocarbon reservoirs. Complex geometries exist, with bounding surfaces and primary strata types often negatively impacting fluid flow. Incorporating the effects of such architectural elements into reservoir models is essential when accurately determining their effect on development strategies. In order to assess their impact, we acquired a small pseudo-3D dataset from the Wahiba Sands, Sultanate of Oman, using ground-penetrating radar (GPR). In this paper we discuss the acquisition, processing and modelling of this dataset. Data are interpreted to be of a small linear dune. Radar stratigraphic units have been interpreted and mapped in 3D; a small-scale analogue reservoir model has been produced. Simulation studies have been conducted to assess the impact of a range of sensitivities, including the affects of permeability contrast, flow direction and capillary pressure. Results indicate that permeability contrasts have a significant impact on recovery, whilst flow direction is the dominant factor. The resulting models may not be directly transferable to a specific subsurface scenario, but the generic spatial information can be a useful guide.