Key geological factors controlling oil displacement efficiency of CO₂ injection in low-permeability reservoirs

Abstract

Carbon dioxide (CO2) flooding is an effective method to enhance oil recovery in low-permeability reservoirs. Studying key geological factors controlling oil displacement efficiency is of great significance to the CO2 injection scheme design in low-permeability reservoirs. Focusing on low-permeable H reservoir in Songliao Basin, China, this paper describes the contact and connection of sand bodies, natural fractures and high-permeability zones with core samples, log data and experiment firstly. After that, the impact of interaction of sand body connection, natural fracture and high-permeability zone on oil displacement efficiency is determined by using geological and dynamic data in CO2 injection area. Results indicate that the connection of single sand bodies between injectors and producters wells primarily controls CO2 flooding in low-permeability reservoirs. Furthermore, coupling of sand body connection, natural fractures and high-permeability zones is the key geological factor governing oil displacement efficiency of CO2 injection in low-permeability reservoirs, where well or generally-connected sand bodies can improve the efficiency significantly. Meanwhile, the dominant seepage channels in other directions have no influence on producers, which is beneficial to improve CO2 flooding efficiency.

A multi-agent deep reinforcement learning method for co2 flooding rates optimization

“…It can be concluded that the P95 optimal case increases the sweep efficiency by decreasing the gas-oil ratio, that is reducing the negative influence results from the gas channeling. The gas channeling happens when the injected gas flows along the high permeability channel with low resistance and too early arrives the production well, which results in the high gas-oil ratio and the low sweep efficiency (Wang et al, 2021). The gas channeling is influenced by the reservoir heterogeneous degree and fluid viscosity difference seriously.…”

“…It has been acknowledged that the displacement efficiency of the completely miscible CO 2 flooding is reach to 100% (Holm, 1987). However, the oil recovery of the CO 2 flooding on site is not all favorable, for the inferior displacement efficiency and sweep efficiency (Zhang et al, 2018; Wang et al, 2021). Because the negative effects result from the miscibility degree, the strong heterogeneous reservoir, the adverse mobility ratio, and the gravity override, etc.…”

Review on Oil Displacement Technologies of Enhanced Oil Recovery: State-of-the-Art and Outlook

“…Nevertheless, CO 2 storage efficiency and oil recovery are estimated and the results can be biased. Wang et al 237 studied the geological factors affecting the efficiency of CO 2 injection in low permeability reservoirs. The results show that the sand body connection, natural fracture and high permeability zone coupling are the key geological factors controlling the efficiency of CO 2 injection in low permeability reservoirs.…”

Immiscible CO2 Flooding Efficiency in Low-Permeability Reservoirs: An Experimental Investigation of Residual Oil Distribution

“…The onshore proven undeveloped oil reserves in China are mainly low-permeability and ultralowpermeability reservoirs (Zhao et al, 2011;Duan et al, 2014). There are many researches in this field with different focuses (Li et al, 2017;Zhang et al, 2020;Wang et al, 2021). Field tests show that CO 2 flooding is a potential option to improve the oil recovery of low-permeability sandstone reservoirs (Zekri et al, 2006;Bourgeois et al, 2011;Wei et al, 2020a), which is the future development direction of enhanced oil recovery (EOR) in these reservoirs (Su et al, 2011;Hao et al, 2016;Li et al, 2019;Wu et al, 2020).…”