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Research Papers: Fundamental Issues and Canonical Flows

Microfluidics Underground: A Micro-Core Method for Pore Scale Analysis of Supercritical CO2 Reactive Transport in Saline Aquifers

[+] Author and Article Information
David Sinton

e-mail: sinton@mie.utoronto.ca
Department of Mechanical and Industrial Engineering and Institute for Sustainable Energy,
University of Toronto,
5 King's College Road,
Toronto, ON, M5S 3G8, Canada

1Corresponding author.

Manuscript received August 5, 2012; final manuscript received December 13, 2012; published online March 19, 2013. Assoc. Editor: Kendra Sharp.

J. Fluids Eng 135(2), 021203 (Mar 19, 2013) (7 pages) Paper No: FE-12-1366; doi: 10.1115/1.4023644 History: Received August 05, 2012; Revised December 13, 2012

Carbon sequestration in microporous geological formations is an emerging strategy for mitigating CO2 emissions from fossil fuel consumption. Injection of CO2 in carbonate reservoirs can change the porosity and permeability of the reservoir regions, along the CO2 plume migration path, due to CO2-brine-rock interactions. Carbon sequestration is effectively a microfluidic process over large scales, and can readily benefit from microfluidic tools and analysis methods. In this study, a micro-core method was developed to investigate the effect of CO2 saturated brine and supercritical CO2 injection, under reservoir temperature and pressure conditions of 8.4 MPa and 40 °C, on the microstructure of limestone core samples. Specifically, carbonate dissolution results in pore structure, porosity, and permeability changes. These changes were measured by X-ray microtomography (micro-CT), liquid permeability measurements, and chemical analysis. Chemical composition of the produced liquid analyzed by inductively coupled plasma-atomic emission spectrometer (ICP-AES) shows concentrations of magnesium and calcium in the produced liquid. Chemical analysis results are consistent with the micro-CT imaging and permeability measurements which all show high dissolution for CO2 saturated brine injection and very minor dissolution under supercritical CO2 injection. This work leverages established advantages of microfluidics in the new context of core-sample analysis, providing a simple core sealing method, small sample size, small volumes of injection fluids, fast characterization times, and pore scale resolution.

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Fig. 2

SEM images of Indiana limestone core samples used in this study (a) intergranular pores; (b) intragranular pores of the dotted red line region in part (a). For both cases, the black areas are pores and gray areas are grains. Scale bars indicate 500 μm in (a) and 10 μm in (b).

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Fig. 3

Pore structure changes due to CO2-saturated brine injection for 3 h (a) before CO2 injection; (b) after CO2 injection; (c) binary image conversion from gray image and histogram. Coronal plane is the horizontal plane, sagittal plane is the vertical plane, and transaxial plane is the axial plane. The image resolution is 4.9 μm per pixel. Black areas are pores and gray areas are grains. The degree of dissolution is significant, with a porosity increase from 18.1% to 26.8% and an observable increase in pore connectivity.

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Fig. 1

Schematic of the experimental setup for the micro-core flooding experiments with pure CO2 and CO2 saturated brine. The system uses a microfluidic chip style holder and connections which simplify the apparatus as compared to conventional core-study methods. The parts inside the dotted line were kept at constant temperature of 40 °C in a water bath. An image of the micro-core is shown inset.

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Fig. 4

Pore structure changes due to pure CO2 injection through the core for 3 h (a) before CO2 injection; (b) after CO2 injection. Coronal plane is the horizontal plane, sagittal plane is the vertical plane, and transaxial plane is the axial plane. The image resolution is 4.9 μm per pixel. Black areas are pores and gray areas are grain. In comparison with CO2-saturated brine flooding (Fig. 3), very little dissolution occurs in this case. Porosity increase is minor, from 17.5% to 19.5%.

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Fig. 5

Pressure drop across the core at each flow rate for permeability calculations before and after core flooding for 3 h at reservoir conditions of 8.4 MPa and 40 °C. (a) CO2-saturated brine core flooding. The linear fit of the flow rate versus pressure drop correlation R2 value is 0.999 for before and 0.996 for after core flooding. (b) ScCO2 core flooding. The linear fit of the flow rate versus pressure drop correlation R2 value is 0.993 for before and 0.966 for after core flooding.

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Fig. 6

Chemical analysis of the produced liquid showing both the Ca2+ and Mg2+ ion concentrations over time. (a) Ca2+ ion concentrations in the produced liquid measured with ICP-AES over the 3 h core flooding experiments with CO2-saturated brine and pure scCO2. (b) Mg2+ ion concentrations in the produced liquid measured with ICP-AES over the 3 h core flooding experiments with CO2-saturated brine and pure scCO2.

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