Comparison of Mesoscopic Fracture Analysis Techniques: A Case Study Near Onion Creek Diapir, Paradox Basin, Utah
Faults and fractures are abundant along the diapir contact in the Onion Creek Diapir in eastern Utah and relate to the mechanisms of diapir formation. Western Onion Creek exhumes two spectacular exposures of the diapir contact and adjacent wall rocks providing two nearly orthogonal transects oriented ∼E-W and S-N. In this study, I used field measurements from natural outcrops and a 3D model developed using Structure-from-Motion/Multiview Stereo photogrammetry to evaluate fracture reservoir development along diapir margins. The 3D-Model was developed using Agisoft Photoscan from ∼3200 ground-based images and was georeferenced using 76 ground control points located with a GPS unit capable of cm level accuracy. Simultaneous measurements of ground control points with a handheld WAAS enabled GPS allowed a comparison of model accuracy with this lower resolution GPS. Although horizontal positions of the handheld GPS were in line with known errors in differential GPS, the vertical estimates from the handheld produced a systematic error. The origin of this error is uncertain but likely is related to local terrain affecting the handheld GPS. The 3-D models were interpreted using Maptek I-site Studio, allowing 3D mapping of fractures and bedding as well as measurements of strike and dip from fractures visible on the model. This allowed direct comparison of model based measurements to field measurements at focus sites. This comparison of model results with field data showed comparable results at all sites where fractures formed clear surfaces on the model and arguably the model results were superior at one site where a second fracture set was revealed by allowing measurements at the top of a cliff, above the site. At complexly deformed sites near the diapir contact, however, measurements made on the model were unsatisfactory, producing measurements that were inconsistent with the field data due to insufficient 3D control and resolution of the model at this site. This problem could have been eliminated had we taken high resolution images of this site as a virtual outcrop, allowing sufficient point density for resolving surfaces on the model. Future studies should consider this approach of developing higher resolution models within larger models where this kind of assessment is needed.
Iraz, Muhammed Tarik, "Comparison of Mesoscopic Fracture Analysis Techniques: A Case Study Near Onion Creek Diapir, Paradox Basin, Utah" (2018). ETD Collection for University of Texas, El Paso. AAI13425086.