Abstract

Capillary desaturation experiments are combined with high-resolution microtomography imaging to understand the impact of wettability on the global and local distribution of fluids in the pore space of sandstone outcrops. Small cylindrical rock samples are cored, imaged in dry state then successively prepared at irreducible water saturation before steps of waterflood. Several samples also go through a wettability-alteration phase in order to expand the range of wettability conditions: namely, oil-wet to mixed-wet. Waterflooding is done at various capillary numbers and injected brine volumes, depending on the case. The entire rock is imaged at voxel resolutions of typically 2 or 4 µm, to ensure a high-quality segmentation.

Global oil saturation results show how the wettability impacts the shape of capillary desaturation curves, in particular, the existence of a critical capillary number. In the nonwater-wet experiments, oil saturation is controlled by a large, highly-connected oil cluster percolating from the inlet to the outlet of the sample. Such results are important for pore-scale flow modeling strategy and validation. We demonstrate that the wettability is not always uniformly distributed along the core despite of the use of classical wettability-alteration protocols, highlighting potential biases in traditional SCAL tests.

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