Fei Jiang

Impact of interfacial tension on residual CO2 clusters in porous sandstone

We develop a numerical simulation that uses the lattice Boltzmann method to directly calculate the characteristics of residual nonwetting-phase clusters to quantify capillary trapping mechanisms in real sandstone. For this purpose, a digital-rock-pore model reconstructed from micro-CT-scanned images of Berea sandstone is filtered and segmented into a binary file. The residual-cluster distribution is generated following simulation of the drainage and imbibition processes. The characteristics of the residual cluster in terms of size distribution, major length, interfacial area, and sphericity are investigated under conditions of different interfacial tension (IFT). Our results indicate that high interfacial tension increases the residual saturation and leads to a large size distribution of residual clusters. However, low interfacial tension results in a larger interfacial area, which is beneficial for dissolution and reaction processes during geological carbon storage. Analysis of the force balance acting on the residual clusters demonstrates that trapping stability is higher in high interfacial tension case, and the interfacial tension should be a controlling factor for the trapping stability in addition to the pore geometry and connectivity. The proposed numerical method can handle the complex displacement of multicomponent systems in porous media. By using this method, we can obtain residual-cluster distributions under different conditions for optimizing the storage capacity of carbon-storage projects.

Estimation of three‐phase relative permeability by simulating fluid dynamics directly on rock‐microstructure images

Given the worlds growing demand for energy, a combination of geological CO2 sequestration and enhanced oil recovery (EOR) technologies is currently regarded as a promising solution, as it would provide a means of reducing carbon emissions into the atmosphere while also leading to the economic benefit of simultaneously recovering oil. The optimization of injection strategies to maximize CO2 storage and increase the oil recovery factors requires complicated pore-scale flow information within a reservoir system consisting of coexisting oil, water, and CO2 phases. In this study, an immiscible three-phase lattice-Boltzmann (LB) model was developed to investigate the complicated flow state with interaction between water, oil, and CO2 systems in porous media. The two main mechanisms of oil remobilization, namely, double-drainage and film flow, can be captured by our model. The estimation of three-phase relative permeability is proposed using the digital rock physics (DRP) simulations. The results indicate that the relative permeability of CO2 as calculated using our steady state method is not sensitive to the initial oil fraction if the oil distribution is originally uniform. Bakers (1988) empirical model was tested and found to be able to provide a good prediction of the three-phase relative permeability data. Our numerical method provides a new tool for accurately predicting three-phase relative permeability data directly based on micro-CT rock images.

The study of heterogeneous two-phase flow around small-scale heterogeneity in porous sandstone by measured elastic wave velocities and lattice Boltzmann method simulation

Two-phase fluid flow is strongly controlled by small-scale (subcore-scale) heterogeneity of porous sandstone. We monitor the heterogeneous/anisotropic two-phase flow (CO2 and water) in porous sandstone and conduct multichannel VP and VP anisotropy measurements under super critical CO2 conditions during CO2 injection (drainage) and water reinjection (imbibition) processes. In drainage, VP shows large reduction (~10%) in all sections of the core sample and changes from the bottom inlet side to upper outlet side. It is considered that VP reduction reflects the CO2 movement in the specimen. The VP anisotropy of the upper two planes indicates clear increase. The results of this experiment indicate the heterogeneous CO2 flow around laminae in porous sandstone and characteristic behavior of these laminae as a barrier for CO2. On the other hand, flow of water is not affected by this barrier. This characteristic CO2 water flow around laminae is observed in the numerical simulation results. This simulation study also indicates that the capillary number is not directly affected on two-phase fluid flow around small-scale heterogeneity in porous sandstone. These results suggest that the small-scale heterogeneity behaves as a CO2 gate and strongly controls CO2 behavior in porous sandstone.

Impact of the kinetic boundary condition on porous media flow in the lattice Boltzmann formulation

To emphasize the importance of the kinetic boundary condition for micro- to nanoscale flow, we present an ad hoc kinetic boundary condition suitable for torturous geological porous media. We found that the kinetic boundary condition is one of the essential features which should be supplemented to the standard lattice Boltzmann scheme in order to obtain accurate continuum observables. The claim is validated using a channel flow setup by showing the agreement of mass flux with analytical value. Further, using a homogeneous porous structure, the importance of the kinetic boundary condition is shown by comparing the permeability correction factor with the analytical value. Finally, the proposed alternate to the kinetic boundary condition is validated by showing its capability to capture the basic feature of the kinetic boundary condition.