An Experimental Study on Carbonated Water Injection of Core Samples from Tight Oil Reservoirs from Ordos Basin

Carbonated water injection (CWI) is considered to be a win-win association for enhancing oil recovery and reducing environmental footprint. Therefore, the study of CWI potential has gained tremendous attention recently. Unfortunately, the dedicated research so far focus heavily on conventional reservoirs. In order to expand the application scope of CWI, the objective of this study is to carry out a coreflooding investigation of core samples from tight oil reservoirs. The experiments were carefully designed to assess the performance of CWI and to quantify the potential of additional oil recovery and CO2 storage capacity under various experimental conditions. We presented the results of a series of CWI coreflood experiments using the reservoir cores of tight sandstone with live crude oil. It is found that the ultimate oil recovery by CWI is higher than the conventional water injection in both secondary and tertiary recovery mode. The complex mechanisms are also investigated including CO2 content of injected carbonated water (CW), oil swelling and viscosity reduction. It was observed that both secondary and tertiary CWI could recover a significant amount of additional oil compared to conventional water injection. The results revealed that the oil recovery would be lower if CO2 concentration is reduced, but the extent of oil recovery reduction would be much less than the level of reduction in CO2 concentration. Oil swelling as a result of CO2 diffusion into the oil raised the pressure, and the reduction of subsequent oil viscosity were amongst the main mechanisms of oil recovery by CWI, which were obtained by the high pressure coreflood models and PVT studies. Higher oil recovery was obtained with the higher permeability and higher carbonation level. At the end of the injection period, an encouraging amount of dissolved CO2 was stored in the brine and the residual oil of the tight sandstone. The experimental results clearly indicate the potential of CWI for improving oil recovery and CO2 storage capacity in tight oil reservoirs. It is particularly attractive for the implementation of CWI for reservoirs that have limited access to large amounts of CO2. To the best of our knowledge, this is the first time to experimentally investigate CWI potential in tight oil reservoirs.