Visualization study of CO2-EOR in carbonate reservoirs using 2.5D heterogeneous micromodels for CCUS

Abstract

Carbon dioxide enhanced oil recovery (CO2-EOR) is one of the significant technologies to increase oil production and also to reduce greenhouse gas emissions. Carbonate reservoirs distribute widely in the world and show an extremely potential for CO2 geological sequestration and enhanced oil recovery, which is a promising technology for CCUS. However, the complex interfacial properties and strong heterogeneity of carbonate reservoirs lead to serious CO2 channeling, resulting in poor carbon sequestration. Microfluidic experiments in synthetic characterization of strongly heterogeneous reservoirs are a novel method to study multiphase flow in porous media. In this study, a heterogeneous micromodel was prepared using sequential photolithography and calcium carbonate (CaCO3) in-situ growth technique, which was used to construct CaCO3 layer by crystallization on the microchannel surface. The micromodel was represented by a 2.5-dimensional (2.5D) network of pores and fractures at different depths, which was used to simulate the natural structure of carbonate reservoir. The morphological and structural characteristics of the 2.5D micromodel were characterized using scanning electron microscopy, atomic force microscopy, and profilometer. The surface wettability was characterized by determining the contact angle. The results showed that a 1–2 μm layer of CaCO3 grew on the microchannel surface, and the channel surface tended to hydrophobicity. The flow behavior of CO2 in reservoirs and the capacity of foam to control CO2 mobility were simulated using 2.5D micromodels. Among them, CO2 channeling is more obvious and realistic in micromodel. Accordingly, foams with and without nanoparticles (NPs) armor were used to control CO2 mobility. The bubble disproportionation, and liquid drainage of bare surfactant foam induced gas–liquid separation in fractures and pores. Subsequent big and soft bubbles illustrated poor CO2 mobility control performance, and the micro-fractures and pores were not effectively swept and stored with CO2. Extremely stable CO2 foam was obtained with the construction of NPs-armor on foam films, more conducive to the trapping of CO2 in bubbles. The findings of this study can help understand complex CO2 flow behavior in carbonate reservoirs and presents a promising method with NPs-armor stabilized CO2 foams for carbon sequestration and enhanced oil recovery in carbonate reservoirs.