Effects of CH4/CO2 multi-component gas on components and properties of tight oil during CO2 utilization and storage: Physical experiment and composition numerical simulation

Abstract

An essential technology of carbon capture, utilization and storage-enhanced oil recovery (CCUS-EOR) for tight oil reservoirs is CO2 huff-puff followed by associated produced gas reinjection. In this paper, the effects of multi-component gas on the properties and components of tight oil are studied. First, the core displacement experiments using the CH4/CO2 multi-component gas are conducted to determine the oil displacement efficiency under different CO2 and CH4 ratios. Then, a viscometer and a liquid density balance are used to investigate the change characteristics of oil viscosity and density after multi-component gas displacement with different CO2 and CH4 ratios. In addition, a laboratory scale numerical model is established to validate the experimental results. Finally, a composition model of multi-stage fractured horizontal well in tight oil reservoir considering nano-confinement effects is established to investigate the effects of multi-component gas on the components of produced dead oil and formation crude oil. The experimental results show that the oil displacement efficiency of multi-component gas displacement is greater than that of single-component gas displacement. The CH4 decreases the viscosity and density of light oil, while CO2 decreases the viscosity but increases the density. And the numerical simulation results show that CO2 extracts more heavy components from the liquid phase into the vapor phase, while CH4 extracts more light components from the liquid phase into the vapor phase during cyclic gas injection. The multi-component gas can extract both the light components and the heavy components from oil, and the balanced production of each components can be achieved by using multi-component gas huff-puff.