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GeoSystems Gas Shale AnalysisOur experience in the evaluation of gas shales started with early work with Mitchell Energy on the Barnett Shale and as part of the group of companies involved in the Gas Research Institute studies of the Appalacian shales. We have developed sample preparation techniques to allow backscatter imaging to be applied to improving the understanding of mineral distribution in shales. The analysis helps to characterize gas shale properties from reservoir quality and mechanical properties. Our typical gas shale analysis integrates the results of petrographic analysis including the evaluation of mineralogy, rock fabric and mineral distribution with geochemical and petrophysical data. These results are then integrated with log data to develop predictory models to allow the population of this data over the total section. A summary of our laboratory services provided for the evaluation and characterization of gas shales are as follows: BACKSCATTER ELECTRON IMAGING (SEM) Examination of ultrapolished flat samples (specially polished thin sections or impregnated sample billets) with the SEM in backscatter electron imaging mode (BSE). Variations in backscatter coefficient (effectively a function of density) are expressed as changes in gray scale. Digital BSE photomicrographs of shale samples (core or cuttings) are processed with image analysis software to yield quantitative information concerning mineralogy as well as volume of micropore space and kerogen volume SHALE THIN SECTION ANALYSIS (rotary or conventional cores) Point count analysis yields quantitative information concerning grain size, sorting, rock composition (volume and distribution of shale, detrital grains and skeletal fragments) as well as volume of authigenic minerals (pyrite, calcite, dolomite, apatite). Thin section analysis also yields information concerning shale fabric, shale particle orientation, vertical heterogeneity and layering. Shale thin sections are impregnated with rhodomine dyed epoxy to facilitate identification of microporosity and microfracturing using luminescent microscopy techniques. Digital color thin section photomicrographs along with written descriptions are provided. SHALE THIN SECTION ANALYSIS (drill cuttings) Cuttings can provide a qualitative description as described above although point count data is not provided. This analysis allows zones with no conventional or rotary cores to be studied and integratied into the interpretations. The X-ray diffraction analysis provides fundamental information concerning shale mineralogy, including variations in clay mineral composition, silicification and authigenic mineral phases (such as apatite, pyrite and carbonate mineral). Analysis provides semi-quantitative determination of bulk rock and/or clay mineralogy. CORE DESCRIPTION – Interpretation of Depositional Environments Foot-by-foot examination and description of core noting vertical variations in lithology, rock texture (grain size and sorting), nature of basal and upper bed contacts, sedimentary structures, fossils, trace fossils, hydrocarbon staining and fracturing. Vertical variations in these rock properties provide the basis for the interpretation of depositional environments. The core description is presented in graphical form and integrated with thin section analysis, routine core (porosity, permeability, saturation) and open hole log data. The graphical display also presents foot-by-foot interpretation of depositional environments. The graphical core description is accompanied by selected core photographs and a detailed written report describing the characteristics of the cored section, the interpretation of depositional environments, sequence stratigraphy and significance in terms of reservoir morphology and orientation. Modern analogs are included. FRACTURE ANALYSIS Foot-by-foot description and classification of fractures by type. Detailed description of the physical characteristics of each fracture set including length, aperture, spacing, hydrocarbon staining, and degree of mineralization. For oriented cores, the strike, dip azimuth and dip magnitude are measured and recorded for each fracture set. Fracture strike and dip azimuth data are presented in rose diagrams and dip magnitude in histograms for each fracture type. Analysis of rose diagrams/ histograms results in the identification of different fracturing styles (extensional or shear) and fracturing history. Rock/Log ModelingPetrophysical, petrographic, geochemical and mechanical property data is integrated with wireline logs to develop a rock/log model that allows for the prediction the following parameters in non-cored wells:
Contact GeoSystems
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