Effects of diagenesis on shale nano-pore structure and implications for sealing capacity

A B S T R A C T: The effect of diagenesis on shale petrophysical characteristics is being investigated as part of a study on shale sealing capacity because of its significance for modelling hydrocarbon charge histories of sedimentary basins. Results to date indicate that diagenesis (degree of cementation and dissolution) significantly affects porosity and inter-connectivity of the nano-pores (0.3~0 nm), the pores constituting the main pore-throats for tight shales. Diagenesis causes tight shale permeabilities to vary over a range exceeding an order of magnitude (113 21 - 6 x 10 2o m 2) and porosities to vary between 1 and 12%. In addition, diagenesis significantly influences shale nano-pore resistance to collapse during compaction and burial, mainly at depth > 2-3 km, affecting hydrocarbon trapping, overpressure and sealing capacities. Dissolution tends to delay the timing of excess pressure pulses, while cementation has a reverse effect. The significance of diagenesis is reduced at shallower depths.

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