The Difference in Damage to Low-Permeability Reservoirs by Different Injection Methods of CO2 Flooding

Abstract

Low-permeability reservoirs have become an important field of oil and gas development in China. CO2 flooding technology is an effective technical means for tertiary oil recovery. Although the asphaltene in the system is deposited in the form of a solid after CO2 injection into the reservoir in contact with crude oil, which causes a certain blockage to the reservoir, the dissolution during the injection process improves the seepage capacity of the reservoir as a whole, and the damage degree of CO2 flooding to low-permeability reservoirs under different injection modes is different. In this paper, the damage degree of asphaltene precipitation to low-permeability reservoirs under different injection modes of CO2 flooding is quantitatively characterized. The mechanism experiment of organic scale plugging after continuous CO2 flooding and CO2–water alternate flooding, the wettability experiment of reservoirs, and the evaluation experiment of CO2–water solution on rock dissolution are carried out, and the variation characteristics of relative permeability curve parameters are evaluated. In this paper, the damage degree of asphaltene precipitation to low-permeability reservoirs under different injection modes of CO2 flooding is quantitatively characterized. The mechanism experiment of organic scale plugging after continuous CO2 flooding and CO2–water alternate flooding, the wettability experiment of reservoirs, and the evaluation experiment of CO2–water solution on rock dissolution are carried out. The variation characteristics of relative permeability curve parameters are evaluated. The results show that the organic scale produced by CO2 flooding will block the pore throat of the rock, but, on the whole, the dissolution caused by the reaction of CO2 and chlorite is stronger, which makes the recovery rate of low-permeability reservoirs effectively improved. The organic scale blockage caused by CO2–water alternating flooding is weaker than that caused by continuous CO2 flooding. The dissolution effect is better and the permeability is higher. It can achieve a better oil displacement effect in pores with a pore size greater than 0.2 μm. On the whole, it can increase the core pore space and seepage channel, so that the recovery rate of low-permeability reservoirs can be effectively improved. This study has important theoretical and practical significance for improving oil recovery in low-permeability reservoirs.