Abstract

The detection, appraisal, and development of unconventional resources invoke some of the greatest technical challenges faced by the hydrocarbon-producing industry today. There exist vast gas and oil reserves in organic mudrocks, but unlocking them in a financially and ecologically viable manner demands the combined and effective implementation of geologic, geophysical, geomechanical, drilling, and production concepts in ways that we have not witnessed before. The very genesis and diagenesis of kerogen give rise to large and complex spatial variations of the storage/flow properties of organic mudrocks, anywhere from nano-size flow confinements to macroscopic sedimentary sequencing (see the accompanying photograph of an outcrop of the Eagle Ford Formation in west Texas). Quantifying the production potential of organic mudrocks requires the integration of geochemical, petrophysical, mechanical, and elastic measurements in nontraditional ways. New effective-medium theories are needed to describe the mechanistic relationships among a multitude of core, borehole, and seismic amplitude measurements. It is necessary not only to detect and quantify presence of kerogen but also to infer geomechanical properties for reliable prediction of hydrofracture efficiency, proppant placement, and fluid stimulation. Experience also shows that the “release” of hydrocarbon present in mudrocks through hydrofractures often involves fast depletion and poor recovery factors. Much work and experience are still needed to assess hydrofracture efficiency and forecast hydrocarbon depletion via in situ or remote measurements (e.g., microseismic amplitude data).

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