Secondary oil migration: oil-rock contact volumes, flow behaviour and rates

Determining oil-rock contact volumes associated with secondary migration is a major challenge due to the heterogeneous nature of the sedimentary structures and petrophysical properties of carrier systems at multiple length scales. In this paper, we argue that migration occurs at, or near, the percolation threshold of the carrier system and show that the oil-rock contact volumes are a function of the heterogeneity of the threshold pressure field of the medium, as well as the orientation of the sedimentary fabric relative to the orientation of the net migration vector. The flow properties are intimately tied to the flow mechanism, which for secondary oil migration is likely to occur via capillary creep. An understanding of the distribution of threshold pressures within a sample volume will enable us to estimate the oil-rock contact volume during secondary oil migration, whether the volume considered is a core plug in size or an entire carrier sequence.