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Title: Self-potential during multiphase flow in complex porous media
Author: Zhang, Jiazuo
ISNI:       0000 0004 6347 2718
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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The rock pore space in many subsurface settings is saturated with water and one or more immiscible fluid phases; examples include non-aqueous-phase liquids (NAPLs) in contaminated aquifers, supercritical CO2 during sequestration in deep saline aquifers, the vadose zone, and hydrocarbon reservoirs. Self-potential (SP) methods have been proposed to monitor multiphase flow in such settings. However, to properly interpret and model these data requires an understanding of the saturation dependence of the streaming potential. This study presents a methodology to determine the saturation dependence of the streaming potential coupling coefficient and streaming current charge density in unsteady-state drainage and imbibition experiments and applies the method to published experimental data. Unsteady-state experiments do not yield representative values of coupling coefficient and streaming current density (or other transport properties such as relative permeability and electrical conductivity) at partial saturation because water saturation within the sample is not uniform. An interpretation method is required to determine the saturation dependence of coupling coefficient and streaming current density within a representative elementary volume with uniform saturation. The method makes no assumptions about the pore-space geometry. We also applied pore network models that can capture the distribution of fluids and electrical charge in real complex porous media to investigate and quantify streaming potential signals during multiphase flow at the pore level. The network modelling results were tested against the interpreted data and experimental data of Estaillades carbonate and St. Bees sandstone, which provided reliable pore-scale explanations of the experimental observations. The results presented here can be used to help interpret SP measurements obtained in partially-saturated subsurface settings.
Supervisor: Jackson, Matthew ; Vinogradov, Jan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral