eming Xu

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

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 instrument-dependent 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 classification 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 classification 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 classification 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 define general geomorphology but is inadequate for fracture definition. The surface classification algorithm can be used to reliably extract fracture and bedding strike and dip angles from the three-dimensional point locations acquired using centimeter-accurate, high-density laser scanner systems.

Creating virtual 3-D outcrop

Because of the high precision of present-day GPS and reflectorless laser technology, geologic information and remotely sensed data (i.e., seismic and GPR grids, wells) can be positioned accurately in 3-D and reconstructed as a virtual image. Hence, we have developed the “virtual outcrop” for applications that require knowledge about the 3-D spatial arrangements of rock types.

Digital Geologic Mapping of the Ferron Sandstone, Muddy Creek, Utah, with GPS and Reflectorless Laser Rangefinders

The traditional approach to geologic mapping consists of sketching, taking orientation and thickness measurements with compass and tape, and noting positions of features on topographic maps or photos. These methods are time consuming, often difficult to realize in rough terrain, and poorly constrain lateral variations in sedimentary facies in relatively flat lying strata. We describe a case study that captures the three-dimensional architecture of sandstone bodies and key geological surfaces such as stratigraphic boundaries and faults using digital capture techniques. The Ferron sandstone in Utah is a superbly exposed ancient delta deposit that provides an improtant outcrop analog to fluvio-deltaic subsurface reservoirs. It has been the focus of many traditional outcrop studies, but here we use a methodology (“cybermapping”) based on GPS with offsets from a continuous ranging mode reflectorless laser rangefinder (“laser sketch”) for collection and analysis of basic stratigraphic and structural data in a relatively remote area. We also show hos this data can be analyzed and visualized in three dimensions. The study area was mapped in two days, which included hiking several kilometers into the area. One-the-fly and rapid static post processing of GPS surveying was used for positioning the reflectorness laser rangefinders; 60,000 points were acquired mapping sedimentological and structural features, terrain, and control points. The resultant quantitative 3D model of the geology and terrain allowed robust geometric visualization and analyses.

Real time and the virtual outcrop improve geological field mapping

New off-the-shelf technologies are providing a quick way for geologists to “capture” observations in the field digitally and may become the standard tools of the early 21st century. A fully contained digital field system capable of decimeter-level accuracy is available now for less than

Recent developments in digital gravity data acquisition on land

10,000 and, since the technologies are rapidly evolving, it should become even more functional, accurate, portable, and cost effective. This system relies on the Global Positioning System (GPS) at various levels of accuracy. Reflectorless laser rangefinders with anglemeasuring capabilities are used to remotely position geologic features with accuracy from centimeters to decimeters relative to the GPS positions. The laser rangefinder can also be used to reference oblique digital photography of outcrops. Data capture with lasers and GPS, integrated with digital photographs and conventional outcrop information, provide a “virtual” outcrop that is fully constrained geometrically and geographically.

Integrated studies of Mexico with gravity, magnetic, and GIS database

Land gravity meters have traditionally been analog, with readings carried out and transcribed manually. The precision (theoretically 10–50 μGal) and the observation rate are very dependent on the skill of the observer. However, the advent of digital recording meters, now offered by several commercial firms, has automated much of the work. As a result, land gravity surveying is both faster and more accurate than in the past and can now be applied to problems where it previously was of little help.

Digital acquisition, analysis, and visualization in the earth sciences

Numerous geologic and geophysical studies in Mexico have been carried out at the University of Texas at Dallas in cooperation with organizations and universities in Mexico. Truly efficient integrated studies require digital databases for computer analysis. Such digital integration has been carried out in Mexico utilizing geophysical, geologic, and associated GIS (Geographical Information Systems) databases.

Integrated Study of Ancient Delta-Front Deposits, Using Outcrop, Ground-Penetrating Radar, and Three-Dimensional Photorealistic Data: Cretaceous Panther Tongue Sandstone, Utah, U.S.A.

Perhaps the greatest obstacle to building an integrated Earth science cyberinfrastructure is the disconnect between the collection of field data and the construction of an associated digital database. This was recognized as a major issue by participants of the Integrated Solid Earth Science Cyberlnfrastructure workshop held at the University of Kansas in 2003, and led to a workshop spanning three days in April 2006, sponsored jointly by the U.S. National Science Foundation and GEON, the Geosciences Network (http://www.geongrid.org). Twenty-eight participants with backgrounds in a broad range of disciplines from institutions in the United States were joined by representatives from Canada, the United Kingdom, and China to explore the motivations and issues surrounding digital acquisition, analysis, and visualization through a series of demonstrations, breakout sessions, and plenary discussions.