Abstract

We introduce a new, cost-effective solution for the characterization of unconventional shale resources based on innovative analysis of drill cuttings. This solution was tested successfully on the Toarcian shales of the Couy-1 well, located in the southern Paris Basin, France. Ten samples of cuttings-sized rock fragments from different depths were subjected to several analytical methods to determine geochemical parameters (LECO and Rock Eval), the mineralogy and texture (QEMSCAN), and the mechanical properties (nanoindentation). Based on the results, the Toarcian shales were subdivided into two mineralogically distinct lithostratigraphic intervals. The Upper Toarcian shales consist of siltstone with a matrix of illitic clays, whereas the Lower Toarcian shales consist mainly of calcareous mudstone with a matrix of finely intermixed calcite and clays. The Young's modulus varies between 12.5 and 25.6 GPa and decreases with increasing TOC content. An interval with high TOC content (> 1.9%) is located between depths of 330 and 350 meter in the Lower Toarcian shales, with a maximum TOC content of 7.6%. A basic set of wireline logs was available and subjected to multi-mineral stochastic log interpretation. By calibrating the log interpretation with the results of the analytical methods, the main petrophysical parameters (TOC content, lithology, porosity, saturation) were successfully determined on log scale. This provides a method for upscaling core and drill cuttings measurements to reservoir scale. In addition, nanoindentation data were used to create a synthetic shear sonic log, allowing for calculation of elastic moduli and brittleness logs. The workflow introduced here provides a method for reliable and accurate characterization of unconventional shale resources based on existing data sets, i.e. drill cuttings and basic log sets. The results can be used for assessment of the hydrocarbon potential and identification of the most prospective zones within source-rock intervals.

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