Petrographic analysis provides a detailed description of the texture (grain size, sorting, and grain contacts), sedimentary structures
(laminations, bioturbation), framework grain composition, authigenic minerals, and types and distribution of macroporosity seen in a thin section. Detailed petrographic techniques can be used in porosity modeling programs and analysis with ultraviolet light can be useful in delineating features that are too small to be easily recognized with standard petrographic analysis.
Petrographic Analysis for Burial History Modeling
A highly detailed petrographic analysis can be used as petrographic input for specific burial history modeling programs and reservoir
characterization models. This type of modal analysis includes a point count (minimum of 300 points) of over 150 categories of framework grains,
cements, and matrix, estimation of amounts of grain coats (typically 50 grains), and grain measurements (generally a minimum of 100 grains).
Petrographic analysis can be used to evaluate the pore system in a reservoir rock. The occurrence and distribution of pore types can be
identified, and pore structure analysis can determine the ratio of primary intergranular pores to secondary leached pores and provide critical
data for evaluation the efficiency of the pore network.
Epifluorscence petrography uses ultraviolet light to emphasize features in a thin section that are difficult to observe with standard
petrographic techniques. This technique is especially useful in identifying and describing microfractures and microporosity in shale thin sections.
Staining techniques can be used in preparing the thin sections to better enable identification of various carbonate minerals. Dual
carbonate stains will differentiate ferroan carbonates (mauve), ferroan dolomite (blue) and calcite (red) above). In cross-polarized light,
these carbonate minerals have similar optical characteristics and can be otherwise difficult to distinguish. Cross-polarized light is used to
easily identify twinned feldspar and quartz overgrowths (below).
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