Volume 34: CCUS Technologies for the Carbon Neutrality: Part II

Experimental investigation of large volume CO2 injection for EOR and sequestration purposes Qi Huan, Li Yiqiang, Liu Zheyu

Abstract

The idea of implementing CO2 injection for reservoir development is shifting from the traditional scheme of injecting small amounts of gas to prevent gas breakthrough, to a large pore volume (PV) injection approach based on expanding the swept volume gradually. To investigate the law and mechanism of EOR and gas sequestration by large PV injection during the CO2 drainage method, a series of large PV CO2 injection experiments were carried out. The cores’ permeability and porosity at different stages of injection were measured, and then the microscopic characteristics and mineral types were analyzed, full-diameter cores were used for large PV CO2 injection experiments to analyze the dynamic characteristics of CO2 injection under the influence of factors such as the degree of miscibility, heterogeneity, and core dip angle. Results showed that with the progress of CO2 injection, the porosity and permeability of the core followed a dynamic law of decreasing first and then increasing. The reaction of calcite, potassium feldspar, and other minerals with acid solutions to form precipitation and segregation, and the loss of fines leading to partial blockage of the throat, both are the main causes of early changes in the physical properties. However, migration and decomposition of the blockage and the development of micro-fractures caused by large PV CO2 injection can further improve the physical properties. Furthermore, it is found that heterogeneity can easily cause premature CO2 gas channeling and reduce the degree of recovery before the gas breakthrough. However, the high degree of miscibility is favorable for improving this situation. The amount of CO2 storage per unit of crude oil produced shows a pattern of rapid decrease followed by a gradual increase throughout the whole drainage stage, and the gas injection volume remains essentially unchanged when it exceeds 2 PV. Therefore, achieving high recovery efficiency and CO2 utilization rate is the fundamental reason for implementing large volume CO2 injection.

Keywords CO2 EOR-sequestration, large volume injection, miscible and immiscible, core flooding, physical property change, carbon neutrality