Mohammad Javaheri

Onset of Convection in CO Sequestration in Deep Inclined Saline Aquifers

CO2-sequestration in deep geological formations has been suggested as an option to reduce greenhouse gas emissions. Saline aquifers are one of the most promising options for carbon dioxide storage. It has been investigated that if the layer of aquifer is deep enough, at depths more than 800 meters, dissolution of CO2 into brine causes density of the mixture to increase. If the corresponding Rayleigh number of the porous medium is enough to initiate convection currents, the rate of dissolution will increase. Early time dissolution of CO2 in brine is mainly dominated by molecular diffusion while the late time dissolution is predominantly governed by convective mixing mechanism. In this paper, linear stability analysis of densitydriven miscible flow for carbon dioxide sequestration in deep inclined saline aquifers is presented. The effect of inclination and its influence on the pattern of convection cells has been investigated and the results are compared with the horizontal layer. The current analysis provides approximations for initial wavelength of the convective instabilities and onset of convection that help in selecting suitable candidates for geological CO2 sequestration sites.

Modelling Mass Transfer Boundary Layer Instability in the CO-Based VAPEX Process

Vapex (vapor extraction) is a promising technique for the recovery of heavy oil and bitumen reservoirs, especially for cases where steam-assisted gravity drainage and other thermal recovery methods are not economical. In the Vapex process, a solvent is injected into the reservoir to reduce the oil viscosity and mobilize it towards the production well. CO2-based Vapex is an attractive option from both economical and environmental perspectives. In CO2-based Vapex, unlike other hydrocarbon solvents, the dissolution of CO2 in oil can result in a density increase of the diluted oil. As a consequence, the diluted oil has a higher density than the immobile oil beneath and a gravitationally unstable diffusive boundary layer is induced, which may lead to natural convection. In this paper, a mathematical model for the diffusive boundary layer in the CO2-oil contact region is developed; and, the possibility of convective mixing is examined using linear stability analysis, based on the amplification of the initial perturbations. It is found that in most experimental cases, depending on the Rayleigh number of the porous medium, convective mixing occurs, which results in higher dissolution of CO2 in oil and thus a higher oil production rate than what is expected from theoretical analysis. This would explain the unexpected higher oil production rate of some experiments in Vapex when CO2 was used as a solvent. In field-scale operations, the results are different. In field cases, since it is almost impossible for the Rayleigh number to exceed the critical Rayleigh number (Rac), convection does not happen.

The Effect of Heavy Oil Viscosity Reduction by Solvent Dissolution on Natural Convection in the Boundary Layer of VAPEX

We have studied the effect of viscosity on natural convection in the boundary layer of the vapor extraction (VAPEX) process. VAPEX is a heavy oil recovery method that uses solvents to reduce oil viscosity, and is a potential process in reservoirs where thermal recovery methods cannot be applied. Natural convection may happen in VAPEX if the solvents that are used to decrease oil viscosity increase the density of the oil. This can especially occur with

Linear Stability Analysis of Double-Diffusive Convection in Porous Media, with Application to Geological Storage of CO2

\text{ CO }_{2}

The Role of Counter-Current Flow in Simultaneous Water and Gas Injection Processes

CO2-based solvents. Reduction of the oil viscosity due to solvent dissolution can have a large impact on the onset of convection by decreasing the critical Rayleigh number. When the viscosity reduction is significant, the critical Rayleigh can decrease up to two orders of magnitude. The transverse Peclet number is also a crucial parameter in determining the critical Rayleigh and onset of convection. Our analysis shows that the longitudinal Peclet does not have a significant impact on the natural convention in VAPEX. When oil viscosity reduction is included in the analysis of boundary layer instability in VAPEX, natural convection may occur in high-permeable reservoirs (where Rayleigh number is high) leading to a greater oil production rate compared with current models where the effect of boundary layer instability has been ignored.

Residual Trapping in Simultaneous Injection of CO2 and Brine in Saline Aquifers

CO2-sequestration in deep geological formations has been suggested as an option to reduce greenhouse gas emissions. Saline aquifers are one of the most promising options for carbon dioxide storage. It has been investigated that if the layer of aquifer is deep enough, at depths more than 800 meters, dissolution of CO2 into brine causes density of the mixture to increase. If the corresponding Rayleigh number of the porous medium is enough to initiate convection currents, the rate of dissolution will increase. Early time dissolution of CO2 in brine is mainly dominated by molecular diffusion while the late time dissolution is predominantly governed by convective mixing mechanism. In this paper, linear stability analysis of densitydriven miscible flow for carbon dioxide sequestration in deep inclined saline aquifers is presented. The effect of inclination and its influence on the pattern of convection cells has been investigated and the results are compared with the horizontal layer. The current analysis provides approximations for initial wavelength of the convective instabilities and onset of convection that help in selecting suitable candidates for geological CO2 sequestration sites.