PARAMETRIC STUDY OF FACTORS AFFECTING CAPILLARY IMBIBITION IN FRACTURED POROUS MEDIA

Open Access
Author:
Lee, Chung-Hao
Graduate Program:
Petroleum and Natural Gas Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 06, 2010
Committee Members:
  • Zuleima T Karpyn, Dissertation Advisor
  • Zuleima T Karpyn, Committee Chair
  • Turgay Ertekin, Committee Member
  • Derek Elsworth, Committee Member
  • Yilin Wang, Committee Member
  • Kamini Singha, Committee Member
Keywords:
  • Imbibition
  • Computed Tomography
  • Fractures
  • Capillarity
Abstract:
Capillarity, gravity and viscous forces control the fluids migration in geologic formations. However, experimental working addressing the simultaneous action of these driving forces as well as the impact of injection flow rate in fractured porous media is limited. Understanding how these variables affect fracture-matrix transfer mechanisms and invasion front evolution in fractured rocks are of crucial importance to modeling and prediction of multiphase ground flow. This study addresses the simultaneous influence of fracture orientation, rock and fluid properties, and flowing conditions on multiphase flow in fractured permeable media at laboratory scale. Displacement of a non-wetting phase (gas or liquid) by capillary imbibition was monitored using X-ray computed tomography (CT). Results were then mimicked using an automated history matching approach to obtain representative relative permeability and capillary pressure curves to further investigate the impact of matrix homogeneity/heterogeneity and boundary shape on the response of the imbibition front. Sensitive analyses, in combination with direct experimental observation, allowed us to explore relative importance of relative permeability and capillary pressure curves to saturation distribution and imbibing font evolution. Experimental observations combined with simulation results indicated the impact of fracture orientation on imbibition front evolution was minimal for the time- and length-scales considered in this investigation. While different injection rates and fluid types showed significant differences in the shape of the imbibing front, breakthrough time, and saturation profiles. The speed and shape of imbibing front progressions were found to be sensitive to matrix water relative permeability, capillary pressure contrast between matrix and fracture, and degree of rock heterogeneity. Results from this work also demonstrated conditions that favor co-current, counter-current, and the coexistence of both displacement mechanisms during imbibition. Co-current flow dominates in the case of water displacing air, while counter-current flow dominates in the case of water displacing kerosene. The balance of capillarity and relative permeabilities has a significant impact of the shape on the invasion front, resulting in periods of co-current and counter-current imbibition. This work presents direct evidence of spontaneous migration of wetting fluids into a rock matrix embedding a fracture. These observations and conclusions are not limited by the geometry of the system and have important implication for water flooding of naturally fractured reservoir and leak-off retention and migration after hydraulic fracture treatments.