2019 AAPG Annual Convention and Exhibition:

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Influence of Mineralogy and Composition on the Geomechanical Properties of the Duvernay Unconventional Liquids Rich Gas Shale Play (Alberta, Canada): a Well Log Perspective


This study integrates outcrop and core observations with well log data and microseismic observations to gain a better understanding of the geological factors affecting the geomechanical properties of the Duvernay shale.

The Devonian Duvernay Formation, one of Canada’s most promising shale plays, has been targeted for shale gas and liquids since 2010. Integration of XRD and micro-hardness tests on core samples has demonstrated that clay and biogenic silica contents are the primary mineral components affecting the geomechanical properties of the Duvernay shale.

In the Kaybob Duvernay basin, although 43 Duvernay cores have been taken in a 7700 km2 area, this still leaves significant regions without any core coverage. Therefore, due to the high degree of vertical and lateral lithofacies heterogeneity within the reservoir, we cannot rely exclusively upon cores for reservoir and geomechanical characterization. For this purpose, indirect tools must be integrated.

To estimate mechanical properties in areas with poor core control, well logs were utilized. In this research, 12 Duvernay cores with available geological and geomechanical data were used to establish relationships between mineralogy and geomechanical properties of the reservoir. Well log signature of the cored wells was matched with geological and geomechanical results from lab analysis on core samples. This made it possible to identify and quantify the volume of the main different mineral phases within the Duvernay shale (silica, limestone, dolostone, pyrite and illite) directly using well logs.

Amongst all the different well logs considered, we will demonstrate that a combination of Spectral Gamma Ray (SGR) and Elemental Capture Spectroscopy (ECS) logs is the most reliable approach to confidently estimate mineralogy, TOC, clay type and clay volume of the Duvernay reservoir. These well log-derived mineral properties integrated with the core-established relationships between mineralogy and elastic properties were successfully applied to calculate mechanical properties of the shales from well logs. The complexity highlighted by the computed rock mechanical model is corroborated by the microseismic response of the Duvernay when undergoing hydraulic fracturing stimulation.

This integrated workflow on characterizing the geomechanical properties of the reservoir even from well log data is a great aid in optimizing the development of the Duvernay Formation and other shale plays around the world.