Key Investigators M. Oostrom, J. Grate, C. Zhang, S. Sundaram Supporting Staff

1. Micromodel Pore-Scale Studies of Caprock-Sealing Efficiency and Trapping Mechanisms Related to CO2 Sequestration Key Investigators M. Oostrom, J. Grate, C. Zhang, S. Sundaram Supporting Staff M. Warner, J. Chun, T. Wietsma The legends PROTECTED INFORMATION and PROPRIETARY INFORMATION apply to information describing Subject Inventions as defined in Contract No. DE-AC05-76RLO1830 and any other information which may be properly withheld from public disclosure thereunder.

2. Knowledge of displacement processes is limited • Subsurface scCO2 sequestration is, to a large extent, affected by porous medium properties, fluid properties, and interfacial interactions. • Key scCO2 sequestration issues are related to: • 1. potential leakage from deep storage location through the caprock. • 2. storage capacity by hydrodynamic and capillary entrapment. From Juanes et al. (2005, WRR)

3. Knowledge of IFT and wettability are crucial • Caprock-sealing efficiency (maximum pressure that needs to be exceeded at interface before scCO2 moves into caprock) is expressed by the Young-Laplace equation: • IFT of brine/scCO2 fluid pairs > 0.020 mN/m in 5 – 45 MPa range (Hildenbrand et al., 2004). However, a literature review has shown that IFTs are poorly characterized and even contradictory. • Wettability of reservoirs or caprock ranges from water-wet to intermediate-wet.

4. Wettability alteration reduces caprock integrity and storage capacity Invading scCO2 might alter wettability. Chiquet et al. (2007) measured wettability changes from water-wet to intermediate-wet at higher pressures for mica and quartz due to decrease of brine pH that follows CO2 dissolution. (Chiquet et al., 2007)

5. Pore-scale experimental capability is needed • Given the lack of data at supercritical conditions and the insufficient understanding of displacement processes at the pore-scale, micromodel experimental investigations into caprock integrity and scCO2 storage capability issues have been recommended by numerous scientists. Increased knowledge should improve current upscaling practices (Chalbaud et al., 2007)

6. Science Questions • What roles do porous medium properties, fluid properties, and wettability (including contact angle hysteresis) play during hydrodynamic (primary) trapping, when scCO2 displaces brine, and during capillary (secondary) trapping, when brine displaces scCO2. • What are the effects of fluid-fluid interfacial tension, pore-size geometry, and wettability on caprock-sealing efficiency? • What are the constitutive relationships between capillary pressure, fluid saturation, relative permeability for pore-scale displacement processes?

7. Research Objectives • Develop a high-pressure, pore-scale flow and transport capability for highly controlled micromodel studies involving scCO2. The capability should include: • -Control of porous medium wettability • -The use of enhanced imaging of micromodels using solvatochromic dyes and/or fluorescent optodes • -Methods to obtain interfacial tension and contact angle data • Increase understanding of pore-scale mechanisms influencing (hydrodynamic and capillary) trapping and caprock integrity for porous medium wettability ranging from water-wet to oil-wet. • Based on pore-scale observations, develop procedures to determine up-scaled constitutive relations between fluid pressures, saturations, and relative permeability.

8. Micromodels In subsurface flow and transport studies, micromodels are representations of porous media etched into silicon wafers, glass, or polymers. Main purposes: • Increase spatial and temporal resolution. • Provide direct quantitative access to processes at the pore scale. • Study pore-scale processes under controlled conditions

9. Ca2+ Outlet CO32- Acid Inlet Microfluidics Experimental Laboratory 1. The ability to conduct micromodel experiments OG5N Ca 2. The ability to fabricate micromodels

10. Microfluidics Experimental Laboratory Current ambient pressure capability consists of Nikon Eclipse TE2000-E microscope, Teledyne Isco100DM Syringe pumps, and micromodels.

11. Micromodel Fabrication Methods - Current PNNL fabrication capability: Wet-etching with acids. - All micromodels used so far have been provided by University of Illinois. Models are fabricated using dry-etching procedure.

12. 1. Coat Si Wafer With PR 2. Align with Mask and Expose to UV light 3. Remove Exposed PR with Developer 5. Remove PR 4. Etch Substrate with Plasma Photoresist (PR) Layer Si Layer Chrome Mask 6. Oxidize Si Surface 7. Anodic bonding with glass SiO2 Layer Pyrex Glass Micromodel Fabrication: Dry Etching

13. Micromodel Fabrication: Dry Etching • Fabrication upgrades at EMSL: • Purchase of mask aligner (~350 K) • Acquisition of dry etcher (~700 K) using ARRA funds Dry-etching micromodel fabrication capability is crucial for this project

14. Capability Development Components • Micromodel fabrication (FY10) • High-pressure micromodel test cell (FY10) • Solvatochromic dye techniques (FY10) • Wettability modification techniques (FY11) • CO2 optode techniques (FY11 and FY12) • High-pressure surface/interfacial tension and contact angle measurements (FY10, FY11)

15. High-Pressure Micromodel System • Operating system consists of • -several pumps • high-pressure cell • imaging ability

16. Solvatochromic Dyes for Displacement Studies

17. Wettability Modifications • Silanization methods will be used to alter the hydrophilicity and hydrophobicity of micromodel internal surfaces. • The nature of silane used will determine the obtained contact angle. • Hydrophobic surfaces will be created of alkyl or long-chain aliphatic monolayers. • Masking techniques will be used to change wettability of desired portion of model.

18. Wettability Modifications • Examples: • Differences in wettability between • Lower and higher permeability zones • Fractured and granular zones

19. Interfacial Tension and Contact Angles • Data are needed to help • design the experiments • interpret results • provide independently obtained parameter values for pore-scale modeling exercises.

20. The project consists of the following FY10 tasks • Task 1. Development of high-pressure cell and assembly/testing of micromodel system. • Task 2. Micromodel fabrication. • Task 3. Development of solvatochromic dye technique • Task 4. Obtain relevant IFT/contact angle measurement • Task 5. Completion of first series of micromodel experiments to study free-phase scCO2 hydrodynamic and capillary trapping mechanisms. • Task 6. Data transfer to modeling project under CSI’s numerical suite.