Multiscale study of chemically-tuned waterflooding in carbonate rocks using micro-computed tomography

Carbonate reservoirs host more than half of the remaining oil reserves worldwide. Due to their complex pore structure and intermediate to oil-wet nature, it is becoming more challenging to produce the remaining oil from these formations. Over the past two decades, chemically-tuned waterflooding (CTWF) has gained the attention of researchers worldwide. Experimental, numerical, and field studies in this area suggest that changes in injected water salinity and ion composition have the potential to increase oil recovery both in sandstone and carbonate reservoirs via wettability alteration. However, the physico-chemical mechanisms involved in improving oil recovery by CTWF remain poorly understood. This could be attributed to the interplay of several mechanisms at the pore-scale resulting in the incremental oil recovery observed at the macro-scale. It is also mainly due to the lack of consistent experimental data across different scales (i.e.: field scale, core-scale, and pore-scale), reducing the possibility of drawing accurate correlations across length-scales. This study proposes multiscale experimental measurements to investigate the effect of oil composition on the performance of CTWF, where continuum-scale floods are performed to investigate the effect of oil composition on oil recovery from oil-wet carbonate rocks by CTWF. In parallel, in-situ pore-scale measurements of wettability and interface curvature alteration are performed. X-ray microtomography is used to perform direct measurement of changes in interfacial curvatures and in-situ 3D contact angle distributions at the micro-scale at different stages of the CTWF. The study also aims at finding a correlation between the magnitude of improvement in oil recovery at the macro-scale and the corresponding magnitude of wettability alteration at the pore-scale at different conditions. This allows for a better understanding of the physico-chemical mechanisms controlling CTWF, which helps advance currently existing CTWF models, as well as result in more well-informed candidate reservoir selection and the development of a workflow to determine the optimum injection brine properties for a given crude oil-brine-rock system.