Gas transport, sorption, and mechanical response of fractured coal

Open Access
Author:
Wang, Shugang
Graduate Program:
Energy and Mineral Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 13, 2011
Committee Members:
  • Derek Elsworth, Dissertation Advisor
  • Derek Elsworth, Committee Chair
  • Chris Marone, Committee Member
  • Jonathan P Mathews, Committee Member
  • Jamal Rostami, Committee Member
Keywords:
  • Gas transport
  • sorption
  • desorption
  • poromechanical
  • coal
Abstract:
Fractured coal exhibits strong and dynamic coupling between fluid transport and mechanical response especially when the pore fluid is a sorbing gas. This complex interaction is due mainly to (i) coal behaving as a dual porosity, dual permeability and dual stiffness medium, (ii) more than 90% of gas being sorbed into the coal matrix, and (iii) cleats providing the principal pathways for transport together with their important control on the strength and stability of coal according to the principle of effective stress. Part I of this dissertation (Chapters I-II) explores the enigmatic role of strains developed in unconstrained sorbing and swelling media and their role in either staunching or enhancing permeability. This is of particular interest in understanding to the behavior of CO2 when injected into sequestration sites, its interaction with caprocks and in the CO2-enhanced recovery of coalbed methane (CBM). Part II (Chapters III-V) examines the role of gas desorption in influencing the mechanical behavior, and in promoting energetic failure in sorbing media. This is of particular interest in understanding the failure processes of underground coal seams (e.g., coal and gas outbursts). Through experimental observations and mechanistic interpretations, process-based models are developed for predicting the fluid transport, sorptive and mechanical response of fractured coal.