The Effect of Pore Topology on Fluid Flow in Carbonates

Abstract

Porosity is the term used to describe the voids in a rock. This porosity is made up of many pores which form a pore network. Pore scale displacement in fluid flow is relevant to a number of industrial and environmental applications. The characteristics of the pore network control the way in which fluid flow occurs throughout the network. Carbonate rocks have particularly complex pore networks due a range of post-depositional processes that modify pore size, shape and connectivity. Although the contributions of factors such as pore throat size and pore network connectivity on fluid flow are reasonably well understood, there is a limited understanding of the effect of pore topology. This research aims to provide a pore-scale picture of the dynamics of fluid flow in both single and multiphase immiscible flow through the use of digital image analysis of fluid flow experiments. The dynamics and patterns of interface displacement as well as the size distribution of trapped oil ganglia were visualised using 2D microfluidic experiments. Different pore topologies resulted in different oil recoveries, however the effect of pore topology was not constant across fluid pairs with different viscosity ratios. Pore size was shown to be a key factor in the recovery efficiency of polymer flooding. This demonstrates that microfluidic experiments offer a methodology to quickly assess a number of different pore topologies under different fluid flow conditions. A range of rock types were imaged in 3D using X-Ray micro-computed tomography to visualise and quantify the range of pore topologies which exist in carbonates. These pore systems were used to assess the reliability of using 2D digital image analysis for permeability prediction, and show that 3D digital image analysis is a far superior technique for reliable pore topological characterisation and permeability prediction. A highly correlated multi-linear regression between permeability and pore topological parameters shows the relevance of pore topologies in predicting permeability. In addition to the investigation of single phase flow in a range of different carbonate pore systems, an investigation into multiphase immiscible displacement in a single carbonate pore system has been conducted. Through the use of synchrotron X-Ray tomographic imaging of an experimental core-flood (oil-brine drainage followed by imbibition) insights into the dynamics of multiphase flow have been gained. The pathway followed by the non-wetting fluid during drainage is strongly linked to the pore topological parameters measured during the analysis of the experiment. Oil initially invades simple pores with low elongation, which are aligned with the flow direction, before invading increasingly complex pores, less aligned to the flow direction. A channelization of flow occurs associated with an area of large, elongate pores. This research demonstrates that pore topology, particularly elongation and orientation to flow direction, has a clear influence on flow and warrants further investigation.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Nima Shokri (Supervisor) & Catherine Hollis (Supervisor)