Single and Multiphase Flow and Transport in Fractured Porous Media

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SINGLE AND MULTIPHASE FLOW AND TRANSPORT IN FRACTURED POROUS MEDIA A DISSERTATION SUBMITTED TO THE DEPARTMENT OF CIVIL ENGINEERING AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

By

Arturo Alejandro Keller

© Copyright by Arturo Alejandro Keller, 1996

SINGLE AND MULTIPHASE FLOW AND TRANSPORT IN FRACTURED POROUS MEDIA © Copyright by Arturo Alejandro Keller, 1996

Abstract
This dissertation summarizes an experimental investigation of flow and transport of nonaqueous phase liquids (NAPLs) in fractured porous media, either in their own phase or as dissolved contaminants. We observed displacement mechanisms at the pore scale when two and three phases are present, using a micromodel, to test the presence of NAPL layers and double displacements. We also conducted single phase tracer experiments, as well as two- and three-phase displacements in real fractured granite and sandstone cores, at a larger scale, using a CAT-scanner. We characterized the fracture aperture distribution at high resolution, to determine the geometry of the pore space, and its influence on flow behavior. The pore space in the micromodels is a simile of a sandstone, which was etched onto a silicon wafer. The sizes of the pores are in the range 3-30 mm, the same as observed in the rock. We conducted the experiments at low capillary numbers (in the order of 10-7). We observed stable NAPL layers between water and air for the waterdecane-air system, even though it has a negative equilibrium spreading coefficient (as do many environmentally significant NAPLs), as well as four different types of double displacements. The NAPL layers are important because they result in very low NAPL saturations at large time scales (months to years). These results are valid for both NAPLs that are less dense than water (LNAPLs) and denser than water NAPLs (DNAPLs), since the formation of the NAPL layers depends only on the contact angles of the interfaces and the angle of the crevices where they are formed, and capillary forces dominate at the pore scale, relative to gravity and viscous forces. The large variation in fracture aperture results in preferential paths for contaminant transport, which results in very early breakthrough. For multiphase flow, capillary forces play a significant role in determining the movement of NAPL from the fracture to the porous matrix and vice versa. These issues, as well as the complex geometry of a network of fractures, have to be taken into consideration when designing a remediation scheme for fractured porous media.

Acknowledgments
First and foremost I would like to thank my wife, Brigitte, who supported my decision to make a radical turn in my life to embark in graduate studies and fulfill my career goals, despite the significant changes it involved in our lives. She has also endured many long hours waiting for me to come home from the lab, and has provided stability to our family by taking charge of our home and our daughters' education. I thank my daughters, Michelle and Nathalie, for their understanding and encouragement to finish this dissertation. I also thank my father and sisters for their support both in my decision to go on to graduate studies and to start my new career. My thanks also to Paul Roberts and Martin Blunt, who provided me with many ideas, insights and comments to help me find a path between the original research proposal and this dissertation. They have been great role models for my future plans. I also thank Lynn Orr and Peter Kitanidis for their comments and suggestions, as well as their encouragement. Last but not least I thank Charlie Werth, for his continuous competitive motivation to finish the Ph. D. I leave Stanford with many good friends.

Table of Contents

Abstract Acknowledgments 1. Introduction 1.1 Problem Statement 1.2 Research Objectives 1.3 Approach 1.4 Dissertation Overview 1.5 References...
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