Pore-scale flow simulation of supercritical CO2 and oil flow for simultaneous CO2 geo-sequestration and enhanced oil recovery

Recently, carbon capture, utilization, and storage (CCUS) with enhanced oil recovery (EOR) have gained a significant traction in an attempt to reduce greenhouse gas emissions. Information on pore-scale CO₂ fluid behavior is vital for efficient geo-sequestration and EOR. This study scrutinizes the behavior of supercritical CO₂ (sc-CO₂) under different reservoir temperature and pressure conditions through computational fluid dynamics (CFD) analysis, applying it to light and heavy crude oil reservoirs. The effects of reservoir pressure (20 MPa and 40 MPa), reservoir temperature (323 K and 353 K), injection velocities (0.005 m/s, 0.001 m/s, and 0.0005 m/s), and in situ oil properties (835.3 kg/m³ and 984 kg/m³) have been considered as control variables. This study couples the Helmholtz free energy equation (equation of state) to consider the changes in physical properties of sc-CO₂ owing to variations in reservoir pressure and temperature conditions. It has been found that the sc-CO₂ sequestration is more efficient in the case of light oil than heavy oil reservoirs. Notably, an increase in temperature and pressure does not affect the trend of sc-CO₂ breakthrough or oil recovery in the case of a reservoir bearing light oil. For heavy oil reservoirs with high pressures, sc-CO₂ sequestration or oil recovery was higher due to the significant increase in density and viscosity of sc-CO₂. Quantitative analysis showed that the stabilizing factor (ε) appreciably varies for light oil at low velocities while higher sensitivity was displayed for heavy oil at high velocities.

A Selection Flowchart for Micromodel Experiments Based on Computational Fluid Dynamic Simulations of Surfactant Flooding in Enhanced Oil Recovery

A selection flowchart that assists, through Computational Fluid Dynamics (CFD) simulations, the design of microfluidic experiments used to distinguish the performance in Chemical Enhanced Oil Recovery (CEOR) of two surfactants with very similar values of interfacial tension (IFT) was proposed and its use demonstrated. The selection flowchart first proposes an experimental design for certain modified variables (X→: porosity, grain shape, the presence of preferential flowing channels, and injection velocity). Experiments are then performed through CFD simulations to obtain a set of response variables (Y→: recovery factor, breakthrough time, the fractal dimension of flow pattern, pressure drop, and entrapment effect). A sensitivity analysis of Y→ regarding the differences in the interfacial tension (IFT) can indicate the CFD experiments that could have more success when distinguishing between two surfactants with similar IFTs (0.037 mN/m and 0.045 mN/m). In the range of modifiable variables evaluated in this study (porosity values of 0.5 and 0.7, circular and irregular grain shape, with and without preferential flowing channel, injection velocities of 10 ft/day and 30 ft/day), the entrapment effect is the response variable that is most affected by changes in IFT. The response of the recovery factor and the breakthrough time was also significant, while the fractal dimension of the flow and the pressure drop had the lowest sensitivity to different IFTs. The experimental conditions that rendered the highest sensitivity to changes in IFT were a low porosity (0.5) and a high injection flow (30 ft/day). The response to the presence of preferential channels and the pore shape was negligible. The approach developed in this research facilitates, through CFD simulations, the study of CEOR processes with microfluidic devices. It reduces the number of experiments and increases the probability of their success.

Pore-scale simulation of water/oil displacement in a water-wet channel

Water/oil flow characteristics in a water-wet capillary were simulated at the pore scale to increase our understanding on immiscible flow and enhanced oil recovery. Volume of fluid method was used to capture the interface between oil and water and a pore-throat connecting structure was established to investigate the effects of viscosity, interfacial tension (IFT) and capillary number (Ca). The results show that during a water displacement process, an initial continuous oil phase can be snapped off in the water-wet pore due to the capillary effect. By altering the viscosity of the displacing fluid and the IFT between the wetting and non-wetting phases, the snapped-off phenomenon can be eliminated or reduced during the displacement. A stable displacement can be obtained under high Ca number conditions. Different displacement effects can be obtained at the same Ca number due to its significant influence on the flow state, i.e., snapped-off flow, transient flow and stable flow, and ultralow IFT alone would not ensure a very high recovery rate due to the fingering flow occurrence. A flow chart relating flow states and the corresponding oil recovery factor is established.

Imaging and characterizing fluid invasion in micro-3D printed porous devices with variable surface wettability

Fluid invasion in porous media widely exists in many applications, such as waterflooded oil/gas recovery, carbon geo-sequestration, water filtration and membrane distillation. The invasion dynamics is significantly affected by the surface wettability, interfacial tension, pore-throat topology and many other parameters. In this work, we experimentally investigate the effect of surface wettability on the multiphase flow behavior, particularly the interfacial dynamics, through direct visualization of fluid invasion in a porous microfluidic device (micromodel). The micromodels have been fabricated by using a micro-stereolithography 3D printer with acrylate-based resins. With a high printing resolution of up to 2 μm, these micromodels successfully mimic the complex pore-throat features of natural porous media (i.e. rocks) based on their thin-section or micro-CT images. Moreover, the transparency of the as-printed micromodel also enables microfluidic flow imaging. By injecting different fluids into surface-modified micromodels, we observe and study the invasion dynamics, including the lateral interfacial curvature, multiphase flow path and fluid trapping behavior, under various surface wettability conditions. By combining optical flow imaging and numerical simulation, we have systematically analyzed the wettability-dependent residue distribution and revealed four different types of trapping mechanisms. This work offers a novel methodology to study microscale flow in porous media with micro-3D printing and multiphase flow imaging.

Pore-scale simulation of wettability and interfacial tension effects on flooding process for enhanced oil recovery

For enhanced oil recovery (EOR) applications, the oil/water flow characteristics during the flooding process was numerically investigated with the volume-of-fluid method at the pore scale. A two-dimensional pore throat-body connecting structure was established, and four scenarios were simulated in this paper. For oil-saturated pores, the wettability effect on the flooding process was studied; for oil-unsaturated pores, three effects were modelled to investigate the oil/water phase flow behaviors, namely the wettability effect, the interfacial tension (IFT) effect, and the combined wettability/IFT effect. The results show that oil saturated pores with the water-wet state can lead to 25-40% more oil recovery than with the oil-wet state, and the remaining oil mainly stays in the near wall region of the pore bodies for oil-wet saturated pores. For oil-unsaturated pores, the wettability effects on the flooding process can help oil to detach from the pore walls. By decreasing the oil/water interfacial tension and altering the wettability from oil-wet to water-wet state, the remaining oil recovery rate can be enhanced successfully. The wettability-IFT combined effect shows better EOR potential compared with decreasing the interfacial tension alone under the oil-wet condition. The simulation results in this work are consistent with previous experimental and molecular dynamics simulation conclusions. The combination effect of the IFT reducation and wettability alteration can become an important recovery mechanism in future studies for nanoparticles, surfactant, and nanoparticle-surfactant hybrid flooding process.

Microscopic modeling of critical pressure of permeation in oily waste water treatment via membrane filtration

Membrane pore blockage is a great concern during membrane processes in oily water treatment.