Efficiency of heavy-oil/bitumen recovery from fractured carbonates by hot-solvent injection

This paper presents an extensive analysis of three different solvents injected through two different rock types under dynamic conditions, at elevated temperatures, to recover heavy-oil/bitumen from fractured carbonates. The main idea was to identify the optimal temperatures needed for maximal recovery by hot solvent injection for a wide range of solvents. We also considered the optimal conditions for effective solvent retrieval for the economics of this type recovery approach. In order to represent a wide range of carbon number solvents, heptane and naphtha were injected at atmospheric pressure and temperatures ranging from 70 to 120 °C and 21.5-100 °C, respectively. Propane was injected at a pressure of 1483-1511 kPa and a temperature ranging from 22 to 60 °C to be in the liquid phase. Indiana limestone (outcrop) and vuggy naturally fractured carbonate samples (outcrop core samples from a producing formation in Mexico) were selected as core samples. Hot solvent was injected continuously through artificially fractured cores followed by hot water (or steam injection) phase for solvent retrieval. The optimal temperatures for heavy oil recovery and solvent retrieval, in the subsequent hot water injection, for each kind of rock sample and type of solvent were determined. The results revealed that heavy oil recovery increase with the solvent carbon number used. Also, it was observed that when the temperature is higher than the saturation value for the given pressure curve, the recovery decreases and the lightest component of the heavy oil are dragged by the gas stream.