Gravity-enhanced Transfer between Fracture and Matrix in Solvent-based Enhanced Oil Recovery (SPE 154374)

Description Solvent injection has been recently considered as an efficient method for enhancing oil recovery from fractured reservoirs. If the mass transfer was solely based on diffusion, oil recovery would have been unacceptably slow. The success of this method therefore depends on the degree of enhancement of the mass exchange rate between the solvent residing in the fracture and the oil residing in the matrix. A series of soak experiments have been conducted to investigate the mass transfer rate between the fracture and the matrix. In a soak experiment, a porous medium containing oil is immersed in an open space containing the solvent to simulate the matrix and the fracture respectively. We use a CT scanner to visualize the process. The experimental data are compared with a simulation model that takes diffusive, gravitational and convective forces into account. Application For oil wet conditions, injection of a liquid (waste) solvent can be considered as a possible alternative for recovery from naturally fractured reservoirs. In the absence of interfacial tension no residual phase trapping occurs. Gravity enhanced transfer leads to practical recovery rates. Results, Observations and Conclusions The initial stage of all experiments can be described by a diffusion-based model with an enhanced C"effective diffusion coefficientsC". In the second stage enhancement of the transfer rate occurs due to the natural convection of solvent in the fracture and its effect on the flow in the matrix. The experiments can be quantitatively mimicked by numerical simulations. We find that transfer rates depend on the properties of the rock, solvent and oil. Technical and economic aspects are further discussed in the paper. Significance The interaction between matrix and fracture is visualized for solvent flooding by means of X-ray computed tomography, which can be used to validate theories of enhanced transfer in fractured media.