Experimental and Analytical Modeling of Gravity Drainage Dominated Heavy-Oil Recovery Under Non-Isothermal Conditions: A Microscale Approach

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Abstract Steam assisted gravity drainage (SAGD) is a well-known example of a non-isothermal gravity dominated recovery application. It is commonly observed that field scale applications of this process yield less recovery than estimated. This requires in-depth analysis of the problem at the pore scale to account for the residual oil saturation in the swept zone. It is still uncertain to what extent pore scale mechanisms, such as the counter and co-current nature of multiphase flow, the trapping mechanism and the distribution of phases, the formation and flow of emulsions, and heat transfer mechanisms affect the process of non-isothermal gravity drainage dominated heavy-oil recovery. Alteration of wettability due to phase change under steam heating and how wettability interacts with spreading coefficients are still enigmatic. In this paper, we used a single capillary tube to mimic an elementary volume in the swept area during gravity dominated displacement under non-isothermal applications. We carried out two-phase (air-oil) and three phase (air-oil-initial water saturation) flow displacements in a capillary tube under isothermal and non-isothermal conditions, varying the air injection rate and the capillary properties. Detailed visualization experiments were carried out to analyze: (1) The effects of oil viscosity, wettability and the spreading coefficient on isothermal and non-isothermal displacement, (2) the interplay among capillary, gravity and viscous (steam injection rates) forces and wettability using different size capillaries, and (3) residual oil saturation and phase distribution in the capillaries (mainly the thicknesses of the wetting and non wetting phases). The analytical calculations based on the experimental observations (measured displacement rates) suggest that at low capillary numbers, the temperature does not have a significant influence in the residual saturation of processed and crude oil. For heavy crude oil this is true for the capillary numbers less than 0.02. Above this threshold capillary number, the oil recovery (and therefore residual oil saturation) is very sensitive to the capillary number, i.e., the injection rate, interfacial tension, and wettability, and to temperature.