Visual Investigation of CO2 Mixing in Water and Oil at Realistic Reservoir Conditions
When CO2 is injected into aquifers or oil fields for permanent storage and enhanced oil recovery purposes, CO2 mixes with the fluid phases (water and oil) present in the reservoir. The CO2 dissolution initiated by the diffusion will increase the density of the liquid-phase, and thereby accelerate the convective flow of CO2. This phenomenon will significantly enhance the underground CO2 storage degree and oil recovery rate. It is important to understand this process more in detail. Many studies are available in the literature where CO2 convective mixing have been experimentally studied in the water phase at the gas phase and liquid phase.
Experiments with visualization of CO2 dissolution into fluid phases, both water and oil in porous media at reservoir temperature and pressure conditions were not available in the literature. Hence, the objective of the presented work was to visually investigate the mixing of supercritical CO2 (sCO2) with water and oil by convective flow at realistic reservoir conditions (pressure and temperature).
Three different scales of experiments were designed at 50 °C and 100 bar. Porous media of different permeabilities were prepared of glass beads of different sizes. CO2 convective mixing experiments into both water and oil were carried out on all scales vertically.
- 2-dim Hele-Shaw experiments
- Pore-scale micromodel experiments
- 3-dim column experiments
In Part 1 of this thesis, at the beginning, it is discussed the details of available experiments in the literature and the theory behind the convective mixing in water and oil.Then, details of the experimental methods, such as materials used, design of the 2-dim Hele-Shaw cells, micromodel, and 3-dim column cell are described. Moreover, details of the concepts behind visualization methods are described. Furthermore, brief experimental procedures together with experimental cases that have been carried out are described.
In the main remarks, a summary of the qualitative visualization results and quantitative analysis are presented as two main parts. 1. CO2 mixing in water 2. CO2 mixing in oil. In both parts experimental results are presented from all three types of experimental setups (i.e. 2-dim Hele- Shaw, micromodel and 3-dim column). Afterwards, scaled experimental data with Rayleigh number vs CO2 transport velocity and dimensionless time are analysed. Effects of the boundary conditions from the experimental cases are discussed. Lastly, relevance of the findings, limitations of the work and future work are suggested with together with summarized main findings in the conclusions.
In Part 2 of the thesis, scientific publications relevant to the main study are presented. CO2 convective mixing experiments in 2-dim Hele-Shaw cell are presented in Paper Ⅰ (low-pressure) and Paper Ⅱ (high-pressure) for both bulk water and homogenous porous media. In Paper Ⅲ CO2 convective mixing experiments in water-saturated heterogeneous porous media presented. Paper Ⅳ is presenting with visual investigations of CO2 convective mixing experiments at pore scale into both water and oil using the micromodel apparatus. Visual investigation of CO2 convective mixing in oil inside 2-dim Hele-Shaw cell are presented in Paper Ⅴ. Paper Ⅵ and Paper Ⅶ are presenting the 3-dim column experiments in water and oil respectively.