This model is the python implementation of the SBT model for simulating heat extraction with closed-loop geothermal systems.
Theoretical description of the model is discussed in: https://doi.org/10.1098/rspa.2015.0494 Example closed-loop geothermal simulations using the SBT model are presented in: https://doi.org/10.1016/j.geothermics.2021.102318 and https://www.sciencedirect.com/science/article/pii/S037565052100273X
The slender-body theory (SBT) simulator is a Python-based tool for simulating the production temperatures, production pressures and heat extraction with closed-loop geothermal systems. The SBT model combines a one-dimensional discretization along the heat exchanger with analytical equations for heat transfer in the rock. This approach allows for fast simulations (i.e., with a computational time of seconds) in comparison with full three-dimensional finite difference, finite volume or finite element models, which may require hours of computational time. The SBT model allows for heat exchanger curvature and captures thermal interference between different heat exchangers (e.g., multiple laterals). However, the model requires constant, uniform and homogenous rock properties and assumes heat conduction only in the reservoir. The SBT model can handle both co-axial (“pipe-in-pipe”) and U-loop type configurations. The co-axial configuration can have injection either in the annulus or center pipe. A U-loop type configuration can have multiple laterals originating from one point and merging at another point.
To simulate co-axial heat exchangers, set the input parameter "clg_configuration" to 1. For simulating U-loop designs, set the input parameter "clg_configuration" to 2. There are two versions of the SBT model, "v1" and "v2", specified in the input parameter "sbt_version". The main differences between “v1” and “v2” is that “v1” assumes constant heat transfer fluid properties and does not calculate the fluid pressure profile, but it does allow for variable injection temperatures and flow rates (including shut-in) and has the fastest computational speed. The “v2” versions require constant injection temperature and flow rate but simulate both the fluid temperature and pressure and allow for variable fluid properties along the heat exchanger and over time. For designs where the heat transfer fluid is approximately incompressible (e.g., water) and undergoes limited temperature increase along the heat exchanger, “v1” would be sufficient, while for simulating fluids undergoing large variations in temperature or that are compressible (e.g., supercritical CO2), “v2” would be required. The SBT v2 models have built-in property tables as a function of temperature and pressure for water and CO2, generated by CoolProp.