Accurate observations and descriptions of the role of heterogeneity on water and CO2 transport and immobilization in porous and fractured geologic media are important for understanding and modeling multiphase conditions present in geologic carbon storage reservoirs. The growth in in-situ imaging has lead to remarkable advancements in understanding and quantification of this complex fluid transport behavior. Despite these advancements, commonly used imaging and experimental methods such as clinical computed tomography, micro computed tomography, nuclear magnetic resonance, and optical imaged micromodels each have limitations. Each modality faces individual challenges with observing fluid advection, dispersion, and diffusion, in 3D geologic porous media. In this work, micro-positron emission tomography (micro-PET), in combination with other imaging methods, is utilized to study a number of challenging transport problems in earth science.