Wettability in complex porous materials, the mixed-wet state, and its relationship to surface roughness

AlRatrout, Ahmed; Blunt, Martin J.; Bijeljic, Branko

doi:10.1073/pnas.1803734115

Cited by 188 publications

(145 citation statements)

References 38 publications

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“…The results illustrate that for a given fluid cluster, a larger deficit curvature dictates a larger contact angle. Similar phenomenological trends that are found in previous publications (AlRatrout et al, , ) are now explained by our geometric approach.…”

Section: Discussionsupporting

confidence: 92%

Probing Effective Wetting in Subsurface Systems

Sun

McClure

Mostaghimi

et al. 2020

Geophysical Research Letters

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Wetting phenomena are of central importance for many natural and technological processes in subsurface geosciences. Surface roughness, chemical heterogeneity, and dynamic effects cause the microscopic contact angle to vary widely in subsurface multiphase systems. These effects must be characterized in a fundamental and transparent way to determine the overall state of wetting. Here, we apply the Gauss‐Bonnet theorem to establish a direct link between the contact angle and bulk fluid topology based on a newly defined term, deficit curvature. The resulting macroscopic measure is able to capture the average effects of complex microscopic variations in contact angle based on intrinsic geometric constraints that are imposed on the curvature of the contact line as a consequence of fluid topology. We show that deficit curvature is able to capture the effects of contact angle hysteresis and describe wetting in multiphase systems where geometrically complex contact lines are present along with surface heterogeneity.

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Section: Discussionsupporting

confidence: 92%

Probing Effective Wetting in Subsurface Systems

Sun

McClure

Mostaghimi

et al. 2020

Geophysical Research Letters

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“…The fact that we do not observe contact angles significantly above 90 • , indicating more strongly oil-wet conditions, is because we find effective values at rest on rough surfaces. Here the brine retained in the corners of the pore space renders the solid, on average, less oil-wet than a smooth surface of the same mineralogy [9,58].…”

Section: E In Situ Contact Angle Measurementsmentioning

confidence: 99%

Minimal surfaces in porous media: Pore-scale imaging of multiphase flow in an altered-wettability Bentheimer sandstone

et al. 2019

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High-resolution x-ray imaging was used in combination with differential pressure measurements to measure relative permeability and capillary pressure simultaneously during a steady-state waterflood experiment on a sample of Bentheimer sandstone 51.6 mm long and 6.1 mm in diameter. After prolonged contact with crude oil to alter the surface wettability, a refined oil and formation brine were injected through the sample at a fixed total flow rate but in a sequence of increasing brine fractional flows. When the pressure across the system stabilized, x-ray tomographic images were taken. The images were used to compute saturation, interfacial area, curvature, and contact angle. From this information relative permeability and capillary pressure were determined as functions of saturation. We compare our results with a previously published experiment under water-wet conditions. The oil relative permeability was lower than in the water-wet case, although a smaller residual oil saturation, of approximately 0.11, was obtained, since the oil remained connected in layers in the altered wettability rock. The capillary pressure was slightly negative and 10 times smaller in magnitude than for the water-wet rock, and approximately constant over a wide range of intermediate saturation. The oil-brine interfacial area was also largely constant in this saturation range. The measured static contact angles had an average of 80 • with a standard deviation of 17 •. We observed that the oil-brine interfaces were not flat, as may be expected for a very low mean curvature, but had two approximately equal, but opposite, curvatures in orthogonal directions. These interfaces were approximately minimal surfaces, which implies well-connected phases. Saddle-shaped menisci swept through the pore space at a constant capillary pressure and with an almost fixed area, removing most of the oil.

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“…In recent years, X-ray μ-CT has been used in the characterization of rock and fluid flow properties (Blunt et al 2013;Bultreys et al 2016a, b). This has extended beyond estimates of simple rock and single-phase flow properties (pore volume, single-phase flow permeability) to include rock mineral composition (Lai et al 2015), capillary pressure from fluid-fluid interfacial curvature (Armstrong et al 2012;Lin et al 2018), and the wetting state from fluid interfacial curvature and in situ contact angle measurements (AlRatrout et al 2018;Andrew et al 2014a;Scanziani et al 2017;AlRatrout et al 2017).…”

Section: Introductionmentioning

confidence: 99%

The Sensitivity of Estimates of Multiphase Fluid and Solid Properties of Porous Rocks to Image Processing

et al. 2019

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X-ray microcomputed tomography (X-ray μ-CT) is a rapidly advancing technology that has been successfully employed to study flow phenomena in porous media. It offers an alternative approach to core scale experiments for the estimation of traditional petrophysical properties such as porosity and single-phase flow permeability. It can also be used to investigate properties that control multiphase flow such as rock wettability or mineral topology. In most applications, analyses are performed on segmented images obtained employing a specific processing pipeline on the greyscale images. The workflow leading to a segmented image is not straightforward or unique and, for most of the properties of interest, a ground truth is not available. For this reason, it is crucial to understand how image processing choices control properties estimation. In this work, we assess the sensitivity of porosity, permeability, specific surface area, in situ contact angle measurements, fluid-fluid interfacial curvature measurements and mineral composition to processing choices. We compare the results obtained upon the employment of two processing pipelines: non-local means filtering followed by watershed segmentation; segmentation by a manually trained random forest classifier. Single-phase flow permeability, in situ contact angle measurements and mineral-to-pore total surface area are the most sensitive properties, as a result of the sensitivity to processing of the phase boundary identification task. Porosity, interfacial fluidfluid curvature and specific mineral descriptors are robust to processing. The sensitivity of the property estimates increases with the complexity of its definition and its relationship to boundary shape.

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Wettability in complex porous materials, the mixed-wet state, and its relationship to surface roughness

Cited by 188 publications

References 38 publications

Probing Effective Wetting in Subsurface Systems

Probing Effective Wetting in Subsurface Systems

Minimal surfaces in porous media: Pore-scale imaging of multiphase flow in an altered-wettability Bentheimer sandstone

The Sensitivity of Estimates of Multiphase Fluid and Solid Properties of Porous Rocks to Image Processing

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