Improving the Performance of Vapor Extraction of Heavy Oil and Bitumen Using the Warm VAPEX Process

摘要

The advantages of solvent-based enhanced oil recovery processes for production of heavy oil and bitumen have always been sacrificed with their low oil production rates and also high solvent costs. Attempts have been made to integrate the solvent and thermal processes to attain better recovery techniques in terms of improved oil production rate, oil quality, and material and energy requirements. In this paper, the process of warm VAPEX is introduced where the injected solvent is superheated. The temperature of solvent vapor (nC5), permeability of packed medium, and the viscosity of oil in place were considered as experimental factors. The VAPEX experiments were performed at 3 temperature levels (36, 43 and 50 °C) using Cold Lake bitumen and Lloydminster heavy oil at two permeability levels (220 and 830 Darcy). The performance of the warm VAPEX process was compared to that of the conventional VAPEX. The packed model was placed in an isothermal bath of circulating hot air to lower the heat loss to surrounding and also to avoid temperature variations of the environment between different trials. During the experiments, the live and dead oil production rates, solvent content analysis, asphaltene content analysis and also residual oil analysis were conducted. The production performance was enhanced, to some extent, when the solvent was allowed to condense, by lowering the temperature of the isothermal bath below the solvent dew point temperature. However, upon a moderate degree of superheating (i.e., the mid-level temperature of 43 °C), the bitumen production was substantially increased at both levels of permeability. The solvent content and solvent-to-oil ratio during the warm VAPEX process decreased with increasing the degree of superheat. Except for the warm VAPEX trial at bubble point temperature, the solvent-to-oil ratios were lower in the warm VAPEX, as compared to the baseline. The asphaltene content analysis showed insignificant deposition of asphaltene during the conventional VAPEX process in which condensation did not occur. On the other hand maximum asphaltene precipitation was achieved at the lowest temperature level (bubble point temperature). At a fixed level of permeability and initial oil viscosity, the residual oil saturation increased with the level of solvent superheating. Therefore, by applying optimal operating conditions, the oil production rate significantly increases while the solvent-to-oil ratio decreases as a result of decreased solubility of solvent in the bitumen. Both factors favor the economy of the VAPEX process. In-situ upgrading of the crude will also occur, which contributes to the improved quality of the produced oil.