3D reconstruction of trace fossils in organic-rich mudstones: implications for core-based studies and impact on shale gas reservoirs.

Graduate Student Seminar: Małgorzata Bednarz, Friday,  March 19^th 2010, 15.30, Room ER3005B.

Shale gas is extracted from low-permeability, organic-rich mudstones. Development of shale gas reservoirs relies on brittleness and enhanced permeability of these fine-grained low permeability rocks. Both brittleness and permeability can be controlled by aspects of the sedimentary fabric that can result from the burrowing activity of grain-selective sediment-feeding organisms.

This work aims to reconstruct the three-dimensional geometries of the common trace fossils found in shale gas reservoir facies in order to characterize the distribution of zones of enhanced brittleness, porosity and permeability. A new reconstruction of a Phycosiphon-like trace fossil from Cretaceous turbidites in Mexico allows a reassessment of its morphology in the light of existing conceptual models. Our palaeobiological model for the formation of the examined trace fossil is fundamentally different to that proposed for Phycosiphon. The reconstructed geometry reveals a doubled volume of the siltstone halo which surrounds the muddy faecal core of the burrow relative to existing models. Incorporation of this kind of understanding into shale gas reservoir characterization is an invaluable addition to routine sedimentological work.