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

摘要

Steam assisted gravity drainage (SAGD) is a well-known example of a non-isothermal gravity dominatedrecovery application. It is commonly observed that field scale applications of this process yield lessrecovery than estimated. This requires in-depth analysis of the problem at the pore scale to account forthe 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 ofmultiphase flow, the trapping mechanism and the distribution of phases, the formation and flow ofemulsions, and heat transfer mechanisms affect the process of non-isothermal gravity drainage dominatedheavy-oil recovery. Alteration of wettability due to phase change under steam heating and howwettability 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 duringgravity 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 isothermaland non-isothermal conditions, varying the air injection rate and the capillary properties. Detailedvisualization experiments were carried out to analyze: (1) The effects of oil viscosity, wettability and thespreading 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 andnon wetting phases).The analytical calculations based on the experimental observations (measured displacement rates) suggestthaat at low capillary numbers, the temperature does not have a significant influence in the residualsaturation of processed and crude oil. For heavy crude oil this is true for the capillary numbers less than0.02. Above this threshold capillary number, the oil recovery (and therefore residual oil saturation) isvery sensitive to the capillary number, i.e., the injection rate, interfacial tension, and wettability, and totemperature.