Maximal oil recovery by simultaneous condensation of alkane and steam.

This paper deals with the application of steam to enhance the recovery from petroleum reservoirs. We formulate a mathematical and numerical model that simulates coinjection of volatile oil with steam into a porous rock in a one-dimensional setting. We utilize the mathematical theory of conservation laws to validate the numerical simulations. This combined numerical and analytical approach reveals the detailed mechanism for thermal displacement of oil mixtures discovered in laboratory experiments. We study the structure of the solution, determined by the speeds and amplitudes of the several nonlinear waves involved. Thus we show that the oil recovery depends critically on whether the boiling-point of the volatile oil is around the water boiling temperature, or much below or above it. These boiling-point ranges correspond to three types of wave structures. When the boiling point of the volatile oil is near the boiling point of water, the striking result is that the speed of the evaporation front is equal or somewhat larger than the speed of the steam condensation front. Thus the volatile oil condenses at the location where the steam condenses too, yielding virtually complete oil recovery. Conversely, if the boiling point is too high or too low, there is incomplete recovery. The condensed volatile oil stays at the steam condensation location because the steam condensation front is a physical shock.