Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720587
Title: Modelling single and two-phase flow on micro-CT images of rock samples
Author: Starnoni, Michele
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2017
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Abstract:
In this Thesis, numerical simulations of single and two-phase pore-scale flow on three dimensional images obtained from micro-CT scanning of different reservoir rocks are presented. For single-phase flow, the petrophysical properties of rocks, namely Representative Elementary Volume (REV), mean pore and grain size, and absolute permeability, are calculated using an integrated approach comprising image processing, statistical correlation and numerical simulations. Two rock formations, one carbonate and one sandstone, are used throughout this Thesis. It is shown that REV and mean pore and grain size are effectively estimated using the two-point spatial correlation function. A comparison of different absolute permeability estimates is also presented, showing a good agreement between the numerical value and the experimentally determined one for the carbonate sample, but a huge discrepancy for the sandstone. For two-phase flow, the Volume-of-fluid method is used to track the interfaces. The surface tension forces are modelled using a filtered sharp formulation, and the Stokes equations are solved using the PISO algorithm. A study on the snap-off mechanism, investigating the role of several parameters including contact angle and viscosity ratio, is presented. Results show that the threshold contact angle for snap-off increases from a value of 28◦ for a circular cross-section to 30-34◦ for a square cross-section and up to 40◦ for a triangular one. For a throat of square cross-section, increasing the viscosity of the injected phase results in a drop in the threshold contact angle from a value of 30◦ when µ = 1 to 26◦ when µ = 10 and down to 24◦ when µ = 20, where µ is the viscosity ratio. Finally, a rigorous spatial averaging procedure is presented, leading to a novel definition of the macroscopic capillary pressure. Simulations results of drainage on the scanned images of the rock samples are used to compare different estimates of the macroscopic capillary pressure. The comparison reveals that, contrary to what is commonly done following the traditional approach, use of surface average for the pressures is more appropriate than that of volume average, when averaging the microscopic balance equations relevant for pore-scale two-phase flows in porous media.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.720587  DOI: Not available
Keywords: Fluid mechanics
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