Abstract:

Under the situation of intensifying CO₂ emissions and increasingly serious environmental problems, carbon emission reduction is urgent. CO₂-EOR is the main means of geological storage of CO₂, but most of the researches on CO₂-EOR at home and abroad are to study the residual oil, and there are few studies on the form of CO₂ storage during oil flooding. In this paper, nuclear magnetic resonance is used to detect CO₂ displacement online combined with numerical simulation is used to study the CO₂ storage morphology and distribution characteristics of different core saturated oil after gas flooding. The results show that the NMR technology combined with the microscopic gas flooding oil numerical simulation method can effectively study the microscopic storage morphology of CO₂. When CO₂ in the core replaces crude oil, it first enters the large pore to drive oil, and after the pressure in the large pore reaches a certain level, the crude oil flows to the small hole throat with uneven distribution of capillary force around it, and the gas continues to drive the crude oil until the small pore pressure accumulates to a certain value in the small pore. Numerical simulations are performed using COMSOL Multiphysics software. Microscopic simulation results shows that CO₂ in large pores mainly exists in the form of continuous free gas, while CO₂ in small pores is first retained in dissolved form. There is no CO₂ completely stored in free gas or dissolved gas in both large and small pores.

Key words: CO₂ flooding, unmiscible, CO₂ micro-storage, NMR, numerical simulation