Tight gas reservoirs exhibit storage and flow characteristics that are intimately tied to depositional and diagenetic processes. As a result, exploitation of these resources requires a comprehensive reservoir description and characterization program to identify properties which control production. In particular, tight gas reservoirs have significant primary and secondary porosity and pore connectivity dominated by clays and slot-like pores. This makes them particularly susceptible to the effects of overburden stress and variable water saturation. This paper describes an integrated approach to describe a tight gas sandstone at the pore scale in 3D. In particular, the primary and secondary porosity of a tight gas sandstone are identified and quantified in three dimensions using 3D X-ray micro-CT imaging and visualization of core material at the pore scale. 3D images allow one to map in detail the pore and grain structure and interconnectivity of primary and secondary porosity. Once the tomographic images are combined with SEM images from a single plane within the cubic data set, the nature of the secondary porosity can be determined and quantified. In-situ mineral maps measured on the same polished plane are used to identify different microporous phases contributing to the secondary porosity. Once these data sets are combined, the contribution of individual clay minerals to the microporosity, pore connectivity, and petrophysical response can be determined. Insight into the producibility may also be gained. This illustrates the role 3D imaging technology can play in a comprehensive reservoir characterization program for tight gas.

Skarn type deposits are important potential resources for Cu, Au, and Ag as well as other strategic metals, which require accurate characterization of the mineralogy, texture and grade for successful processing and environmental management. The mineralogy of these deposits and of the resulting tailings has traditionally been examined using transmitted light microscopy, cathodoluminescence, X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. In the present study, the Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN®) technology was applied to rapidly acquire spatially resolved mineralogical data from tailings associated with a Cu(Au,Ag) skarn type deposit. The resulting modal and textural data provided relevant additional information on the distribution of the ore minerals, including detail on the trace minerals, grain size distributions, and mineral associations. The following benefits of detailed mineralogical knowledge from this study can be pointed out: it improves the lithotyping of these complex deposit types and will benefit their ore processing strategies; it allows inferences to be made about the environmental behavior of the tailings, namely the acid mine drainage potential; it provides data about deportment of penalty and toxic elements, which are specifically As, Te, and Sb. Thus, particular applications of QEMSCAN include assessments of the acid consumption of the mineral assemblages (mainly assured due to calcite and dolomite) and of the abundance, distribution and mobility of potentially toxic elements, such as As.

High resolution Backscattered Electron images (BSE) can be used to extract textural information such as grain and pore size; specific surface area; and so forth. Based on this information porosity and permeability can be estimated. On the other hand, low resolution Energy Dispersive Spectroscopy Imaging (EDS) provides valuable information about the mineralogy and chemical composition of the rock samples. Scanning Electron Microscopy (SEM) instruments are capable of generating BSE images of core and cuttings samples in a relatively short period of time at very high resolutions. The story is different if EDS images are also acquired. For example EDS images at 20 μm point spacing usually do not take longer than 30 minutes to be captured, but if point spacing is reduced to 10 μm, then measurement time increases approximately by 4 times. This paper proposes a new methodology to combine high resolution BSE images with low resolution EDS images and to use the combined textural and mineralogical information in order to improve grain segmentation, grain size calculations as well as estimating porosity and permeability in rock samples. This methodology starts with the acquisition of the BSE and EDS images looking for an optimal relationship between acquisition time and image quality. Secondly the registration and fusion of the two images is performed and advanced image processing techniques are applied to extract information that corresponds to underlying physical characteristics such as porosity and permeability. Results of this methodology are encouraging, 4 to 5 μm point spacing BSE images have been registered and fused with 20 μm EDS images and excellent grain segmentation has been achieved. Calculated porosity values show a good match with helium porosity core data and estimated permeability using the Kozeny-Carman equation gives results in the same order of magnitude. This new approach saves time, operating costs and enable geoscientists to collect valuable rock data at the micro-scale level. Furthermore, this information can be used to estimate important rock properties when integrated with other data sources to improve reservoir characterization especially in cases where information is scarce or difficult to obtain.