Hot Solvent-Assisted Gravity Drainage in Naturally Fractured Heavy Oil Reservoirs: A New Model and Approach to Determine Optimal Solvent Injection Temperature

Hot solvent-assisted oil recovery is a low emission-intensity oil recovery method from heavy oil resources. This method is particularly promising for fractured reservoirs where the application of current thermal methods may involve challenges associated with heat loss and early breakthrough. In this study a new model of heat and mass transfer for oil recovery from a single matrix block of a naturally fractured reservoir using a hot miscible solvent is developed. Because of the difference in magnitude between thermal and mass diffusivities, heat diffuses beyond the solvent-oil interface and there is no significant convective heat transfer. This results in a reduction of oil viscosity in the center of the matrix block and a vertical convective flow pattern instead of a pattern parallel to the oil solvent interface observed during cold solvent injection. Using this model, optimization graphs are developed to perform a fast qualitative assessment of the applicability of a hot solvent-assisted gravity drainage process in naturally fractured reservoirs with various parameters without the need of complex simulations and experiments. An algorithm is presented to estimate the recovery time or target injection temperature of potential hot solvent-assisted oil recovery processes using these optimization graphs. This can reduce computational time and provide a quick evaluation of the hot solvent-assisted gravity drainage process in naturally fractured heavy oil reservoirs.