Capillary-Driven Flow in Fractured Sandstone

Open Access
Author:
Karpyn, Zuleima Tharays
Graduate Program:
Petroleum and Natural Gas Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
November 16, 2004
Committee Members:
  • Abraham S Grader, Committee Chair
  • Phillip Michael Halleck, Committee Member
  • Turgay Ertekin, Committee Member
  • Derek Elsworth, Committee Member
  • Chris Marone, Committee Member
Keywords:
  • Capillarity
  • flow in fractures
  • imbibition
  • experiment
  • fracture aperture
Abstract:
Studies concerning flow in fractured rocks have important applications in hydrocarbon recovery, hydrogeology, and environmental remediation of subsurface spills. To properly design immiscible flow processes, it is crucial to understand fracture-matrix transfer mechanisms. The main goal of this work is to identify key parameters affecting fracture-matrix flow during capillary imbibition in fractured sandstone. The author attempts to unfold the following questions: • Is there a physical correlation between fracture aperture distribution and the properties of the surrounding rock? • How does the geometry of a fracture determine fluid occupancy and preferential flow paths within it? • What is the relative contribution of co-current and counter-current flow during capillary imbibition in fractured rock? Two major experiments are described in the present study: one focused on fluid occupancy in the fracture void, and the other focused on fracture-matrix flow during spontaneous capillary imbibition. These experiments were performed in layered Berea sandstone with a single longitudinal fracture. The artificially created fracture was oriented perpendicular to the natural bedding of the rock for the case of spontaneous capillary imbibition. Samples were initially vacuum saturated with the desired resident phase. During the capillary imbibition experiment, small amounts of a wetting phase were introduced into the bottom of the fracture, allowing it to imbibe and exchange places with the resident non-wetting phase through the fracture-matrix interface. Fluid occupancy in the fracture as well as saturation changes during the imbibition process were monitored using Micro-Computed Tomography (MCT). Numerical simulation of various experimental scenarios was carried out. Experimental observations combined with simulation results indicate that the fracture exhibits strong capillary behavior. Experimental observations also show strong correspondence between fluid invasion in the matrix and variations in porosity in the matrix bedding planes. Different porosities correspond to different permeabilities and capillary pressure curves. Co-current and counter-current flow occur during capillary imbibition in a fractured rock. Fluid accessibility in the fracture is also an important factor governing imbibition in fractured media. Fluid discontinuity and occupancy are key parameters affecting fluid accessibility between the matrix and fracture domain. Other factors affecting imbibition are interfacial tension, fracture roughness, and presence of micro-fractures.