Experimental study on replacement behavior of crude oil by CO₂ based on nuclear magnetic resonance technology

Abstract

Due to the high viscosity of Jimsar crude oil and the lipophilicity of the reservoir, CO₂ has an excellent performance in development of Jimsar shale oil. However, previous studies mostly focused on CO₂ fracturing, but the replacement of crude oil by CO₂ is rarely reported. Therefore, we conducted research on oil replacement by CO₂ through systematical experiments. Firstly, we designed an experimental approach based on nuclear magnetic resonance to quantify the replacement ratio of oil. Next, a series of experiments were conducted for analyzing the effect of pressure, soaking time, permeability, and fractures on replacement ratio. Finally, oil-water imbibition experiments were conducted to compare its development effect with CO₂ replacement for target reservoir. The study shows that the replacement capacity of CO₂ for crude oil increases with pressure. In the experiment, the replacement ratio increases from 27.46% (10 MPa) to 56.70% (40 MPa) after 24 hours. On the microscopic scale, the crude oil in large pores is replaced out firstly, then the smaller pores. And on the macroscopic scale, the replacement of crude oil is from outside to inside. High permeability and fractures in the core promote the intrusion of CO₂ into the core, raising the replacement ratio significantly. Since Jimsar reservoir is oil-wet, the oil recovery of oil-water imbibition is far less than that of CO₂ replacement. The minimum pore through which oil can be exploited by oil-water imbibition is 1 μm, while for CO₂ replacement the value is 0.08 μm. This study provides fundamental for CO₂ increasing oil recovery in Jimsar shale oil.

Graphical Abstract

Keywords:

• Jimsar shale
• soaking experiment
• replacement of crude oil by CO2
• nuclear magnetic resonance
• T2 spectrum
• oil-water imbibition

Additional information

Funding

This paper is supported by Project of Research and application of key technologies for exploration and development of continental medium and high maturity shale oil (Grant No. 2019E-26).