Reservoir Engineering: Contact Angle Measurement
1. To what extent, the ‘gravitational force’ plays a crucial role:
(a) when the fluid flow remains to be perfectly horizontal;
(b) when the fluid flow remains to be perfectly vertical;
(c) when the fluid flows at an angle towards gravity; and
(d) when the fluid flows at an angle against gravity; - towards dictating whether
(i) the cohesive forces between the liquid molecules remain to be stronger than the adhesive forces between the solid and liquid molecules (and as a result, the liquid balls up and tending to avoid contact with the surface); or,
(ii) the solid/liquid adhesion remaining stronger than the cohesion within the liquid molecules (and as a result, no drop forms and the liquid tending to spread on the surface)?
Whether such role of ‘gravity’ would remain to be similar both @ laboratory-scale as well as @ field-scale?
If not, how would ‘contact angle’ measured @ laboratory-scale would be able to provide ‘an inverse measure of wettability’ @ field-scale?
2. In the absence of an atomically flat and chemically homogenous ideal surface – associated with a real field reservoir scenario; (for that matter, even with laboratory-scale experimental conditions), whether force per unit length OR energy per unit area would remain to be more apt towards the determination of contact angles (where, the formation of a perfect spherical cap geometry remains ruled out)?
3. Which one of the following essentially controls the wettability @ laboratory-scale? (a) the advancement of solid/liquid interface to a certain area; OR (b) the advancement of three-phase contact line to a certain length; upon placing a sessile droplet on a substrate?
4. Which one of them plays a very crucial role in ceasing the apparent contact angle @ field-scale?
(a) the surface roughness;
(b) the chemical heterogeneity of surface; or
(c) physical/chemical properties of reservoir fluids.
5. Even, if we manage to measure advancing, receding and static apparent contact angles along with the details of contact angle hysteresis – towards determining the properties of surface; whether the nature of surface roughness, chemical heterogeneity and shear hydrophobicity @ laboratory-scale and @ field-scale would more or less remain to be the same?
6. Why does apparent contact angle remain to be significantly different from (a) advancing contact angle;
(b) receding contact angle; and
(c) local contact angle?
7. How important is the ratio of drop-size to wavelength towards contact angle measurement?
8. How exactly could we get rid-off stick-slip movement of drops; and what exactly happens when the drop volume exceeds 10 micro-liters – towards contact angle measurement?
1) Fluid flow at interface: Article Fluid Flow with Dynamic Contact Angle: Numerical Simulation
Gravity inclusion: Article Measurement of contact angle under different gravity generat...
2) I'm not sure this is what you want, but: if the surface is not a well-defined surface but has defects, you don't actually measure the surface energies you are looking for but that of a defected surface which is probably an average value over various energies. I would expect that usually the trend would go towards "wetting is more likely".
3) The wettability is an absolute parameter, the hysteresis effects you describe don't affect this parameter, but are error sources in the exact determination of it.
4) I'm not a field-scale guy, so no specific idea. In general, all of them have an influence.
5) Regarding the scales, again I can't say more than in 2
6) Hysteresis phenomena are very common in contact angle measurements, it may have to do with a metastable situation being reached and requiring the proper activation to overcome. I think the notion that values determined from sessile bubble experiments are considered more accurate than sessile drop experiments have something to do with it. But of course sessile bubble may be hard to realize outside the lab.
7) What wavelength? Are you measuring your contact angles with a interferometer? Is equation (1) here what you are looking for? Article Interfacial shape and contact-angle measurement of transpare...
8) I would assume the bigger your drop gets, the bigger the influence of gravity deformations will become, but I don't know a paper on it.
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