Visual Investigations on the Oil Recovery and Sequestration Potential of CO₂ in Naturally Fractured Oil Reservoirs

Abstract

CO 2 sequestration into geologic formations such as oil reservoirs, coal beds and aquifers is a possible way to reduce the emissions of this anthropogenic gas into the atmosphere. Among these, sequestration into oil reservoirs while enhancing oil recovery is one of the most feasible ways as the additional oil recovery would offset the cost of CO 2 sequestration operation. We postulate that the matrix, the main source of oil, could be a good CO 2 storage medium. Hence, we focus on the matrix-fracture interaction during CO 2 injection into naturally fracture oil reservoirs (the Weyburn and Midale fields are good examples for this case) in this paper.Proper design of this process is essential to maximize both the amount of CO 2 sequestered and oil recovered. In this cooptimization process, miscibility, oil viscosity, matrix properties (permeability, porosity, pore characteristics, wettability, etc.), fracture properties (permeability, orientation, connectivity), injection rate, gravity, and the physical state of CO 2 play a critical role. Clear understanding of the contributions of these properties on the dynamics of matrixfracture interaction is essential in designing EOR and CO 2 sequestration application.In this paper, the dynamics of CO 2 injection was studied experimentally. 2-D glass-bead models with a fracture in the middle were prepared and pentane was used as solvent to displace the kerosene or mineral oil to mimic miscible CO 2 displacement. The focus was on the displacement patterns and solvent breakthrough controlled by matrix fracture interaction and pore scale behaviour of solvent-oil interaction for different matrix (wettability), fracture and injection conditions (rate, vertical vs. horizontal injection) as well as oil viscosity. Besides the visual investigation, the produced fluid was analyzed to calculate the solvent cut and oil recovery.It is believed that the visual understanding of the process will provide substantial information for further modelling studies.

Pore-Scale Investigation of the Matrix−Fracture Interaction During CO2Injection in Naturally Fractured Oil Reservoirs

“…This, however, requires more CO 2 injection at higher rates compared to lower rates, as also shown in our earlier fully, first-contact, miscible experiment. 24,25 At 1200 and 1500 psi, injected CO 2 at 50 mL/h mixed with the fracture fluid first. Figures 9 and 11 show the development of the miscible front in the fracture and the interaction with the oil in the matrix.…”

“…In a recent study, Javadpour and Fisher provided information about the fabrication of new generation micromodels and a new technique to monitor saturation changes without coloring the fluids. 23 In our earlier studies, 24,25 we conducted visualization experiments displacing different types of oil with a first-contact miscible solvent in the single-fractured matrix under different orientation and rate conditions. In these studies, the matrixfracture interaction during first-contact miscible displacements was investigated by experimental and simulation studies.…”

“…In our earlier studies, , we conducted visualization experiments displacing different types of oil with a first-contact miscible solvent in the single-fractured matrix under different orientation and rate conditions. In these studies, the matrix−fracture interaction during first-contact miscible displacements was investigated by experimental and simulation studies.…”