Energi Simulation IAP on Carbon Utilization and Storage, Ryosuke Okuno

Overview

This project aims to develop technologies for aqueous CO2 nanobubble (NB) dispersion for enhanced oil recovery from conventional and unconventional reservoirs. The central hypothesis in this project is that the CO2-rich phase generated near the fronts of oil displacement in CO2 NB injection can greatly enhance oil recovery. Previous studies on carbonated water injection (CWI) showed a markedly increased oil recovery factor upon breakthrough (RFBT) in comparison to the control experiment with brine with no CO2 when the CO2-rich phase was generated near the displacement fronts. CO2 NB is expected to promote this new mechanism of oil recovery by substantially increasing the CO2 concentration in water beyond the inherent solubility. Aqueous CO2 NB injection is also expected to be much simpler and less expensive than CO2 injection because a small amount of CO2 is injected as an effectively homogeneous aqueous fluid (e.g., 1 tonne of CO2 in 15 tonnes of brine).

Background

The NB technology is increasing its applications in various industries, such as agriculture, wastewater treatment, mineral processing, fishery, and medical imaging. However, these prior applications are focused on open systems near or at atmospheric pressure. Such aqueous bubbles are unstable with a large number density in the absence of continuous input of energy.

We have studied methods of generating an aqueous NB fluid that can contain a large amount of an immiscible gas or gas mixture at elevated pressure in a controlled and scalable manner without using stabilizers, such as surfactants and polymers. The technology makes the gaseous species stably dispersed in the aqueous fluid as nano-scale bubbles and dissolved molecules. These two modes of containment can collectively make the overall concentration of the gaseous species much greater than its thermodynamic solubility in the aqueous fluid. By taking advantage of pressure, the technology finds its most promising applications in subsurface processes and high-pressure surface processes that are mediated by aqueous fluids.

Aqueous NB EOR will be similar to CWI from an operational point of view; however, the former can greatly enhance the displacement of oil by CO2 because it can generate a CO2-rich phase locally near the displacement fronts where the metastable aqueous phase (CO2-NB) releases CO2 to the oleic phase while the nanobubbles of CO2 with capillary pressure release CO2 to the surrounding aqueous phase. The in-situ formation of the CO2-rich phase is expected to be much more significant with CO2-NB than with CWI.

Figure 1. Corefloods of dead oil with NaCl brine, CWI slightly above the CO2 solubility (eCW), and CO2-NB.

Figure 2. Huff-n-puff experiments of live oil with Kentucky SS using miscible CO2 (supercritical) and CO2 NB.

Ways forward

• Steady-state generation of aqueous CO2 NB
• PVT tests with oil and thermodynamic modeling
• Systematic comparison between CO2 NB and CO2 injection in corefloods and huff-n-puff
• Fractional flow analysis
• Numerical simulation techniques
• Shear stability of CO2 NB
• Nitrogen NB