Probing the intrinsically oil-wet surfaces of pores in North Sea chalk at subpore resolution
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Ultimate Oil recovery from chalk reservoirs is limited by many factors - including the grain size and the surface properties of the small mainly biogenic calcite particles that chalk is made off . Wettability, the tendency for water or oil to spread over a surface, of the particle surfaces is one of the controlling factors for the effectiveness of water flooding, one of the most common methods to improve oil recovery in Chalk reservoirs. Understanding surface wetting and its variability at scales smaller than the pore dimension will potentially provide clues for more effective oil production methods. We used atomic force microscopy-mediated adhesion and elasticity mapping derived from maps of force curves, to examine 5 x 5 µm2 areas of internal pore surfaces, using a tip functionalised to make it hydrophobic. We investigated chalk samples from inside a drill core sample from the Danish North Sea that had been drilled in a water-bearing formation. At this site, the chalk has never seen oil, though at other locations, the same stratigraphic horizon with the same rock properties is known to be a productive oil reservoir. Thus the properties of the investigated particle surfaces are inherent to the chalk, not a product of later migration of oil into the reservoir, which is known to alter the wettability of the surfaces. The data indicated distinct patches, with diameters ranging from 500 to 50 nm, which appears to have different wettability The size of the patches is significantly less than the size of the chalk particles and the data thus indicate variability in the wettability across an individual particle surface. Hydrophobicity varied by factors of more than 15, and elasticity, by more than 30. Some areas were both soft and hydrophobic but for many others, there was no correlation between hardness and adhesion properties. From these results, we propose that the macroscopic parameter, “wetting” is partly an inherent property of the chalk, and is linked directly to material present on the particle surfaces at the time of their deposition. The hydrophobic material, which varies in surface concentration at the nanometer scale, has produced mixed-wet internal pore surfaces.
Udgivelsesdato: 2009
Udgivelsesdato: 2009
| Originalsprog | Engelsk |
|---|---|
| Tidsskrift | Proceedings of the National Academy of Science of the United States of America |
| Vol/bind | 106 |
| Udgave nummer | 15 |
| Sider (fra-til) | 6071-6076 |
| Antal sider | 5 |
| ISSN | 0027-8424 |
| Status | Udgivet - 2009 |
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