The inability to accurately resolve subseismic-scale structural discontinuities such as natural fractures represents a significant source of uncertainty for subsurface modeling practices. Fracture statistics collected from outcrop analogs are commonly used to fill the knowledge gap to reduce the uncertainty related to fracture-induced permeability anisotropy. The conventional methods of data collection from outcrops are tedious, time consuming, and often biased due to accessibility constraints. Recent advances in virtual outcrop-based methods in fracture characterization enhance conventional methods by streamlining data collection and analysis. However, certain limitations and challenges exist in virtually obtained fracture data sets. The ability to identify fractures that are both exposed as lineations and as planes from a digital outcrop model depends heavily upon the fidelity and resolution of its surface display of RGB color, reducing the capacity of light detection and ranging (lidar) to the resolution of the scanner-attached camera. In the present study, we adopted a hybrid approach, combining lidar-based digital outcrop models and georeferenced high-quality photomosaics, providing improved texture maps in terms of pixel density compared to maps generated from on-scanner camera images. With this approach, the effects of truncation on digital outcrop models were limited, giving the ability to detect fractures that would otherwise be aliased from on-scanner camera imagery. The fracture system developed within the exposures of the Mississippian Boone Formation, an outcrop analog for age-equivalent reservoir objectives in Mississippi Lime hydrocarbon play, was characterized using conventional and virtual outcrop-based techniques. To test the fidelity of the virtual fracture extraction approach, fracture orientation statistics generated from lidar are compared with equivalent data sets collected using traditional surveys. The results suggest that terrestrial lidar, coupled with referenced gigapixel photomosaics, provide an effective medium for fracture identification with the capacity of resolving fracture characteristics with sufficient fidelity to potentially act as conditioning data for discrete fracture network models, making it an attractive alternative tool for fracture modeling workflows.
This article presents results of mercury in surface waters from Hunza River basin, Northern Areas, Pakistan. Small‐scale gold mining activities along the Hunza and Gilgit rivers are long known to be discharging mercury in the amalgamation and roasting processes. Previous studies reported high mercury concentrations in soils close to mining operations as well as serious health problems for miners. However, none of the studies have focused on the level of contamination in aqueous environments. This is the first study on the investigation of source and fate of sediment and river‐borne mercury in the Hunza River. The samples collected near gold panning sites showed higher mercury concentrations than critical levels established by the U.S. Environmental Protection Agency. The observed dissolved mercury concentrations ranged from 5.10 to 25.25 ng/l, whereas particulate‐bound mercury ranged from 4.85 to 154.62 ng/l. Particulate‐phase mercury corresponded to more than 75% of the total observed mercury concentrations for all of the sampled rivers. Thus, suspended sediments represented the major pathway of the riverine mercury transport. A mass balance calculation suggested an annual mercury flux of 48.6 g/km2 into the Hunza River basin. The samples collected from the most affected river, the Shimsal River, averaged to have 108 ng/l total mercury. This amount was close to the average soil mercury data of 151 ng/l as reported by the Pakistan Mineral Development Corporation in 2001. The dominant source of contamination was shown to be the leaching of large quantities of mercury from the mercury‐rich sediment and flood plain soil into the rivers, rather than the direct release from mining activities. Significant decrease in both dissolved and particulate‐bound mercury concentration downstream of Attabad Lake suggested that mercury is being accumulated or consumed in the lake. Although minimization or elimination of mercury loses from the mining process seems important for the well‐being of the miners, preventing the remobilization of accumulated mercury is equally important in mercury control in this region. Copyright © 2014 John Wiley & Sons, Ltd.
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