Experimental and numerical studies of CO2 injection into watersaturated porous medium: CO2 dissolution-diffusion-convection process

  • Titly Farhana Faisal

Student thesis: Master's Thesis

Abstract

One of the fundamental physical phenomena related to CO2 injection and storage in geological saline aquifers is the dissolution-diffusion-convection process of CO2 in the brine-saturated rock formation. Positive buoyancy of supercritical CO2 causes the CO2 to rise up and form a thin layer of free phase CO2 beneath the formation seal. Dissolution of injected CO2 within the ambient brine will increase storage security. CO2 saturated brine is 0.1-1% heavier than underlying brine. This will lead to density-driven convection which will greatly accelerate the mass transfer rate of CO2 into the brine and reduce time for solutal trapping compared to only molecular diffusion. Due to the very large timescales involved, reservoir modeling is the only feasible method to investigate this important phenomenon.The aim of this work is to produce results at laboratory scale via experiments and simulations which will inform studies of this long-term dissolution process at the reservoir scale. To visualize this convective phenomenon, experiments using transparent Hele-Shaw cells of size (20cm by 30cm) were performed as flow within the narrow gap of Hele-Shaw cell is mathematically analogous to 2D flow in porous medium. CO2 gas introduced at the top of the cell dissolves at the gas-water interface. The higher density at top leads to gravitational instability and consequently convective fingerings appear depending on the permeability of the system which is function of the Hele-Shaw cell aperture squared. Dissolution of CO2 reduces pH of the solution which is visually tracked using a pH tracking dye called Bromocresol green and captured at regular intervals using a CCD camera followed by image enhancement techniques. Experiments are repeated with variations in permeability and cell aspect ratio to vary the characteristic Rayleigh number (~1800 to 28000). The onset time for the beginning of instability is found to increase for lower permeability, which is consistent with linear stability analysis predictions. Corresponding simulations for the experimental parameters were performed using STOMP (Subsurface Transport Over Multiple Phases) Simulator developed by the Pacific Northwest National Laboratory's Hydrology Group. Comparison of experimental and numerical results shows very good agreement in terms of convection pattern, advancement and timescales.
Date of Award2012
Original languageAmerican English
SupervisorMohamed Sassi (Supervisor)

Keywords

  • Convective Clouds
  • Water-Saturated

Cite this

'