Applications of digital outcrop models: two fluvial case studies from the Triassic Wolfville Fm., Canada and Oukaimeden Sandstone Fm., Morocco

Abstract

The application and benefits of employing digital outcrop models (DOMs) are discussed using two Triassic fluvial case studies to demonstrate data collection and integration methods. Developments in data analysis techniques are examined to demonstrate their utility for collecting meaningful and reliable statistical information needed to build realistic stochastic reservoir models. To establish a significant geostatistical dataset a large number of accurate observations are required. It is difficult to get the necessary statistics using subsurface data alone, due to the limited resolution and/or areal coverage of respectively seismic and well data. Outcrop studies are, therefore, commonly utilized to provide analogue statistical information (e.g. channel width, length, thickness and thickness vs. width ratio). Traditional data collection methods used in the field are however largely restricted to areas with (easy) physical access, or using remote observations with limited accuracy, such as photographic methods.Digital data collection techniques such as LiDAR (Light Detection and Ranging) and differential GPS allow more accurate measurements, as well as from previously inaccessible locations, to be taken of sedimentary architecture. The technique generates much larger volumes of measurements, as the area from which accurate data can be extracted is increased. This offers a more meaningful statistical dataset, hence reducing uncertainty in the final reservoir model.Both case studies, the Oukaimeden Sandstone Formation (OSF), Morocco and Wolfville Formation, Canada, are from Late Triassic braided fluvial systems. The OSF dataset has been used to illustrate how geometric information of channel width versus thickness relationships (W:T) are collected using a projection plane technique. The results show W:T variations between 3.49:1 in the Lower Oukaimeden member, 1.54:1 in the Middle Oukaimeden member and 3.75:1 in the Upper Oukaimeden member, demonstrating the observed architectural evolution of the fluvial system. The Wolfville Formation case study shows how DGPS in combination with LiDAR data has been used to more accurately map faults to obtain statistical information on fault orientation (NE-SW) and length (mean ¼ 38.3 m and median ¼ 18.2 m). Another applied analysis technique utilizes a facies classified point-cloud to aid surface correlations between sedimentary logs and construct a log based correlation panel from which estimates of facies frequencies are derived.

Ground-based and UAV-Based photogrammetry: A multi-scale, high-resolution mapping tool for structural geology and paleoseismology

“…11; Supplementary Material). Rock textures and fabrics can be produced with high fidelity, using processing and visualization tools such as Agisoft Photoscan™, which perform well in both the ground-based studies discussed here and UAV-based studies (Turner et al, 2013). Photo-based models also compare favourably with laser scanning techniques when used to identify joints, discontinuities and orientations (e.g.…”

“…Turner et al (2012) report the absolute accuracy of the orthorectified images produced from this method is typically < 400 mm. Using this direct georeferencing technique, absolute accuracies are dominated by the navigation grade GPS errors, estimation of the camera focal length and interior/exterior orientation parameters and imprecise synchronization between the GPS receiver and camera (Turner et al, 2013). This series of steps is now largely implemented in off-the-shelf software products such as Photoscan (Table 1).…”

“…DSLR) with fixed optics, collecting slightly convergent imagery (Wackrow and Chandler, 2011;James and Robson, 2014), and surveying the outcrop using flight lines from 2 orthogonal directions (P. Kovesi pers comm.). Recently, Turner et al (2013) obtained large improvements to the absolute accuracy of the direct georeferencing technique with modifications to the onboard GPS receiver, synchronization between the GPS receiver and camera and corrections between the GPS antenna and camera position. Absolute accuracies of 100e200 mm were achieved (Turner et al, 2013).…”

“…Recently, Turner et al (2013) obtained large improvements to the absolute accuracy of the direct georeferencing technique with modifications to the onboard GPS receiver, synchronization between the GPS receiver and camera and corrections between the GPS antenna and camera position. Absolute accuracies of 100e200 mm were achieved (Turner et al, 2013). Similar improvements are only likely to accelerate in the next few years, and the need for GCPs may well be eliminated in the near future at the point where direct georeferencing techniques achieve similar accuracies to GCP studies constrained by differential GPS.…”

The application of outcrop analogues in geological modelling: a review, present status and future outlook

“…Early studies interpreted geology on to this point cloud (e.g. Bellian et al 2005) but, more recently, the points are triangulated and images are draped on to the surface generating a photo-realistic model that can be used to generate highly accurate and precise measurements of geobodies in the outcrop (van Lanen et al 2009;. More recently, helicopter-mounted LiDAR has been used to collect very large datasets, km to tens of km long (Buckley et al 2008b;Rittersbacher et al 2013).…”