Analytic Investigation of Convection During Conduction Heating of a Heavy-Oil Reservoir

Abstract

The assumption of constant temperature is often valid for the operation and analysis of most conventional oil reservoirs; however the average behaviour of reservoirs exposed to thermal flooding is non-isothermal. In addition to being nonisothermal, heated reservoirs are characterised by non-uniform temperature distribution. Where the heating mechanism is conduction, most analyses ignore convection (including natural convection) in the overall heat balance. However, the induced temperature gradient affects fluid properties (especially viscosity and density) and their spatial distribution.In this paper, possible buoyancy-induced natural convection is investigated by simulating one-dimensional vertical temperature profiles of a semi-infinite reservoir column, fully saturated with undersaturated heavy oil, subjected to conduction heating from the bottom. Using a realistic temperature dependence of the density and viscosity of typical Athabasca bitumen, vertical distributions of in-situ oil density, velocity and Nusselt number consistent with the induced temperature gradient are established. The simulation results indicate that at any time, oil density increases vertically away from the heat source, a condition that is gravitationally unstable, with a potential for fluid-redistribution, triggering convection. In this study, the magnitude of a Nusselt number is used as a proxy for the relative importance of natural convection. Although it is shown that free convection can be important, its significance depends on the duration of heating as well as rock and fluid properties. Consequently, we argue that the convective heat-transfer, in addition to temperature and time-dependent variations of oil density and viscosity, should be considered in realistic models of thermal recovery of heavy oil, even if the heating philosophy is "apparently" conduction.

Coupling Mechanism of Multiple-Thermal-Fluid Multi-Cycle Stimulation in Ultra-Heavy-Oil Reservoirs

“…According to the heating range and value of increasing formation temperature , dimensionless distance and dimensionless temperature curves are made, as shown in Figure 4. The inflection points of dimensionless distance and dimensionless temperature curves are used to divide the function areas of different heat transfer modes [17]. The inflection point is located at the 1/3 position (10 m) in the high-temperature oil-viscosity-reducing zone and the outer boundary (30 m) of the high-temperature oil-viscosity-reduction zone.…”

Effect of Oil Mass Flow Rate on Temperature Profile in Oil Wells

“…Several models are proposed for the distribution of temperature in specific geothermal and natural reservoirs and for the thermal injection model well-tested [3,4]. Lawal and Vesovic [5] developed a one-dimensional heat transfer model to predict the distribution of temperatures for various conditions. Authors used the relation between the temperature-dependent oil density and the viscosity of a bitumen reservoir.…”