Outcrop fracture characterization using terrestrial laser scanners: Deep-water Jackfork sandstone at Big Rock Quarry, Arkansas

Abstract

Determination of fracture orientation can be an important aspect of structural analysis in reservoir characterization. The availability of ground-based laser scanner systems opens up new possibilities for the determination of fracture surface orientation in rock outcrops. Scanners are available in low-sample-density, low-accuracy, and fast, high-sample-density, high-accuracy models. These automatic laser scanner systems produce enormous volumes or "clouds" of point data at an instrumentdependent accuracy and resolution, which can be at the millimeter level. This huge volume of data calls for an automated and objective method of analysis. We have developed a surface classifi cation algorithm based on a multipass partitioning of the point cloud. The method makes use of both spatial proximity and the orientation of an initial coarse-grained model of the point cloud. Unsupervised classifi cation of surface sets is demonstrated herein using the new algorithm. Both previously mentioned types of scanners have been used to map the Jackfork sandstone outcrop at Big Rock Quarry in Little Rock, Arkansas. We apply the surface classifi cation algorithm to these data to extract fracture surface orientations from the point cloud. The effectiveness of these new technologies when applied to fracture analysis is clearly demonstrated in this example. It is also shown that the low-density, low-resolution type of scanner is adequate to defi ne general geomorphology but is inadequate for fracture defi nition. The surface classifi cation algorithm can be used to reliably extract fracture and bedding strike and dip angles from the three-dimensional point locations acquired using centimeter-accurate, highdensity laser scanner systems.

3D characterization of fracture systems using Terrestrial Laser Scanning: an example from the Lewisian basement of NW Scotland

“…Figure 4d shows an image of the Kinlochbervie coloured point cloud that formed the basis for the fracture interpretation. Detailed descriptions of TLS data acquisition and interpretation techniques are given in (Ahlgren and Holmlund 2003;Bellian et al 2005;Hodgetts 2013;Kokkalas et al 2007;McCaffrey et al 2008;Olariu et al 2008;Wilson et al 2011). …”

“…(Gillespie et al 1993;Odling et al 1999). Many outcrops, however have the potential to provide access to 3D information, and a number of studies have demonstrated the potential for Terrestrial Laser Scanning (TLS) to provide an improved description of the 3D spatial properties of fracture systems exposed in bedrock outcrops (Ahlgren & Holmlund 2003;Trinks et al 2005;Olariu et al 2008;Seers et al 2014). Here we report a recent study on a potential outcrop analogue for the basement lithologies of the Rona ridge in which we used TLS to investigate fracture attributes and how they varied spatially in the hangingwall of a nearby major normal fault.…”

Common problems encountered in 3D mapping of geological contacts using high-resolution terrain and image data

“…New remote sensing techniques such as LiDAR [e.g., Lim et al, 2010;Jaboyedoff et al, 2012;Abellán et al, 2014], Photogrammetry [e.g., Sturzenegger and Stead, 2009;Firpo et al, 2011;Curtaz et al, 2014] and gigapixel photography [Stock et al, 2011;Lato et al, 2012;Kromer et al, 2014] have significantly improved the representation of three-dimensional surfaces during the last decade, especially for steep and inaccessible rock cliffs, allowing the development of high-resolution 2D geological maps [Putnam et al, 2014]. These techniques have also been used for the characterization of petroleum reservoir analogues and fracture systems at outcrop level [Olariu et al, 2008;Rotevatn, 2009;De Souza et al, 2013;Hodgetts, 2013;Penasa et al, 2014], texturing of high-resolution panoramas on digital outcrop models [Buckley et al, 2008[Buckley et al, , 2010Minisini et al, 2014] and 3D geological/mineralogical mapping [Sima et al, 2012;Kurz et al, 2013;Murphy et al, 2013]. However, from a practical point of view, it is still very difficult to work in a fully 3D environment, drawing 3D lines or folded surfaces, because: a) Common 3D geological modelling software packages (MOVE, GSI3D, PETREL, etc.)…”

Point clouds from oblique stereo-imagery: Two outcrop case studies across scales and accessibility

“…is presented within a virtual environment that can be rotated in three dimensional space and used for geological interpretation [Bellian et al, 2005]. DOMs have found particular use in the fields of reservoir studies [Pringle et al, 2004;Enge et al, 2007;Janson et al, 2007;Rotevatn et al, 2009;Fabuel-Perez et al, 2010], structural studies [Ahlgren and Holmlund, 2003;Sagy et al, 2007;Olariu et al, 2008] and in cliff erosion and natural hazards studies Rosser et al, 2005;Jaboyedoff et al, 2007;Kuhn and Prüfer, 2014] as well as in the generation of virtual field trips [McCaffrey et al, 2010]. Central to the generation of a DOM is the digital elevation model that describes the morphology of the outcrop.…”