Wettability and wettability alteration at the pore- and nano- scales
File(s)
Author(s)
Rüecker, Maja
Type
Thesis
Abstract
It has been well documented that Darcy scale multiphase flow is significantly influenced by the wettability of the fluid-solid system. So far this impact can only be determined through costly and time intensive experiments. To predict observations at the core-scale, smaller scale parameters influencing the results need to be determined and assessed. In this work core-scale wettability responses were compared to nano-and pore- scale observations by combining micro-computed tomography and atomic force microscopy. Amott spontaneous imbibition tests were used to determine the core-scale wettability. A relationship was found between wettability and the capillary pressure applied during the sample initialization with crude oil. Samples initialized with higher capillary pressure showed an oil-wet behaviour, while samples initialized with lower capillary pressure appeared mixed-wet leaning towards the water-wet side. CT waterflood experiments showed that ganglion dynamics behaviour, in which the connectivity of the oil phase changes via break-up and coalescence, is enhanced in mixed-wet systems. The oil-filling events appeared larger and more frequent than in water-wet samples. Contact angle distributions often used to assess wettability at this length scale were found to not reflect the wettability of the sample correctly. The CT images showed thin oil-layers, just above the resolution of the image covering the grains of the rock, while all contact angles obtained from the same images appeared water-wet. These apparently contradictory results were targeted with a new approach based on atomic force microscopy. Surface roughness measured with AFM was used for drainage simulation assessing the surface coverage by the two fluids present in the rock. The surface coverage at connate water-saturation varied from 1.5% - 50% depending on the capillary pressure applied. These results were compared to in situ fluid film measurements on the nano-scale, which showed a surface coverage of 60 % when the initialization protocol for mixed-wet sample was followed. This small scale wettability pattern may lead to the different responses observed at larger scales. The conducted experiments show how the different aspects of wettability across length scales impact capillary pressure and relative permeability at the core-scale.
Version
Open Access
Date Issued
2018-06
Date Awarded
2019-01
Copyright Statement
Creative Commons Attribution Non-Commercial No Derivatives licence
Advisor
Blunt, Martin
Luckham, Paul
Sponsor
Shell Global Solutions International B.V.
Publisher Department
Earth Science and Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)