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SAGD technology has been successfully and widely applied in the development of superheavy oil and oil sand projects. Before normal SAGD process, some preheating ways are often needed to realize interwell hydraulic connection, and this means that determining reasonable SAGD conversion timing from the preheating stage is an essential precondition for good performance. Previous numerical simulations or qualitative analysis of temperature fall-off data are often adopted in the industry, but they have deficiencies in terms of dependent on static geological model or insufficient data utilization. Therefore, on the basis of the temperature and pressure monitoring process comparison in China's superheavy oil and Canada's oil sand projects, this paper proposed a temperature fall-off interpretation model to obtain thermal diffusivity and preheating radius at different measurement points along the horizontal section by combining an unsteady thermal conduction model under constant heating power of wellbores in the radial coordinate system and approximately unsteady thermal conduction model with constant wellbore temperature and Fourier's law of thermal conduction. Besides, the duration time, interpretation method, and application flow chart of temperature fall-off test were presented. Then, it was validated to successfully determine the timing of SAGD conversion from the preheating stage by an example combining with tracking numerical simulation, temperature inflection point analysis, and index analysis during the partial-SAGD and initial SAGD stages. The findings of this study can help determine the SAGD conversion timing from the preheating stage simpler and faster especially for the case of long horizontal well section deployed with more temperature measurement points. [ABSTRACT FROM AUTHOR]

To improve the thermal effects of solvents on heavy oil reservoirs and realize the combined action of multiple flooding mechanisms, such as solvent heating and extraction, without steam mixing, based on the M Block heavy oil reservoir in Canada, three sets of comparative hot solvent-assisted gravity drainage experiments under different temperatures and pressures were carried out through an indoor three-dimensional (3D) physical simulation device. The development characteristics of the solvent chamber in the hot solvent-assisted gravity drainage technology were studied under different pressures and temperatures, and the recovery factor, cumulative oil exchange rate, and solvent retention rate were analyzed. The results showed that due to the effect of gravity differentiation, the development morphology of the solvent chamber could be divided into three stages: rapid ascent, lateral expansion, and slow descent. When the temperature was constant, the reservoir pressure decreased, the recovery rate increased, the cumulative oil exchange rate increased, and the solvent retention rate decreased; when the pressure was constant, the temperature increased, the viscosity of heavy oil decreased, the recovery rate increased, the cumulative oil exchange rate increased, and the solvent retention rate was low. Additionally, the study also showed that for hot solvents in different phases, the use of hot solvent vapor not only required less injected solvent but also exhibited a high oil production rate, which shortened production time and reduced energy consumption. Moreover, the oil recovery rate was higher than 60%, the solvent retention rate was lower than 10%, and the cumulative oil exchange rate was higher than 3 t / t , which constituted better economic benefits and provided a reliable theoretical basis for onsite oilfield applications. [ABSTRACT FROM AUTHOR]