Effect of Natural Convection Patterns on Optimal Location and Size of a Heat Sink in a Geothermal Reservoir
نویسندگان
چکیده
Geothermal energy resources such as geopressured geothermal brine (GGB) reservoirs and hot saline aquifers (HSA) can be potential clean energy resources provided the heat extraction from the subsurface is done in an economic and environmental friendly manner. In the proposed study, we are simulating the heat transfer processes around a downhole heat exchanger placed in a long lateral wellbore in a confined geothermal reservoir. Natural convection patterns in saturated porous media that are induced due to the heat extraction process influence the overall amount of heat extracted. Verification and validation studies are presented to evaluate the predictive capability of a thermal reservoir simulator. Several parametric studies (15 cases) are presented to quantify the role of the natural convection on the optimal location and the length of the downhole heat exchanger (DHE). INTRODUCTION During the geothermal heat extraction process, the fluid flow in the porous media could control the heat transport rate both by natural convection as well as forced convection. The role of natural convection is typically small as compared to the forced convection and depends on reservoir geometry as well as properties. However, at the time scales of long production life of the geothermal resource, natural convection could play a significant role. For geothermal resources such as GGB and HAS, natural convection may be significant during and after heat extraction to impact the overall heat extracted. The present simulation study focuses on the fluid flow and heat transfer processes around a DHE placed in a long lateral wellbore in a confined saturated geothermal reservoir. The DHE is represented as a horizontal heat sink with linearly varying specified temperature located in the saturated aquifer layer. Several parametric cases are studied to include the effect of DHE length and its vertical position on the heat transfer rate as well overall heat extracted. NATURAL CONVECTION SIMULATION IN A GEOTHERMAL RESERVOIR Natural Convection Natural convection is the fluid motion generated by density differences due to temperature gradients. The ratio of the natural convection to the conduction is given by a dimensionless group, Rayleigh number (Eq. 1).
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