Methods to measure contact angles in scCO2-brine-sandstone systems

Numerous methods are used to measure contact angles (θ) in multiphase systems. The wettability and θ are primary controls on CO2 residual trapping during Geologic Carbon Storage (GCS) and determining these values within rock pores is paramount to increasing storage efficiency. One traditional experimental approach is the sessile drop method which involves θ measurements on a single image of droplets. More recent developments utilize X-ray micro-computed tomography (CT) scans which provide the resolutions necessary to image in situ θ of fluids at representative conditions; however, experimental micro-CT data is limited and varied. To further examine θ distributions in supercritical-CO2-brine-sandstone systems, a combination of manual and automated θ measurement methods were utilized to measure θ using both sessile drop and micro-CT images of two sandstone cores. The purpose of this work was threefold: (1) compare two current and two new θ measuring methods using micro-CT images of scCO2-brine-sandstone systems; (2) determine how traditional experimental method (sessile drop) θ results compare to in situ θ results (micro-CT); and (3) determine if the Matlab Contact Angle Algorithm (MCAA) from Klise et al. (2016) can be used to measure θ scCO2-brine-sandstone systems. One of the two new methods utilizing open-source software resulted in comparable average θ and θ ranges to the primary manual measuring method (Andrew et al., 2014b) reported in literature that requires commercial software to complete. An additional new method involves immersive interaction with micro-CT image volumes that no other software currently provides. Both processes are found to be promising for future work. θ measured using micro-CT images at in situ conditions result in a broader θ distribution than those measured using sessile drop images. These findings suggest some pores are intermediate-wet in an in situ sandstone system and factors other than interfacial tension influence trapping. Lastly, MCAA θ results consistently produced broader θ distributions and higher average θ than the manual θ measurements. This is a result of some automated measurements incorrectly identifying directional quantities leading to skewed results. MCAA is still promising for future work with careful attention to data interpretation.

Duke Scholars

Author Laura Elizabeth Dalton Civil and Environmental Engineering