Thermal Near-well Region Reservoir Simulation Solution for Wellbore Simulations

Temperature distributions in the reservoir near-wellbore region are important parameters that must be calculated precisely in many operations because both pressure and temperature deplete fast in the near-well region. Most wellbore simulators use an overall constant heat transfer rate for the reservoir-wellbore heat balance. This approach is far from accurate especially for thermal applications as temperature profiles and thermal properties of the fluids in the wellbore and reservoir change both in space and time, especially with inflow. This paper presents the solution of a coupled combined wellbore-near-well region thermal simulation during drilling, well testing, completion design, fracturing job design, temperature sensor placement, etc. The solution presented in this paper features a nodal network of a wellbore simulator and a thermal hydraulic near-wellbore reservoir simulator. Energy and momentum balance are implicitly solved at each time step. The simulation domain is fully discretized along the longitudinal and radial directions in wellbore proximity (3-10m). For testing and validation of the developed solver, a 3D finite volume computational fluid dynamics (CFD) simulator was used, and good agreement was demonstrated in tested cases. For one of the validation examples, an injection of hot water into the formation was modeled. The simulator accurately predicted both the propagation of the water front and temperature field variation with time. In contrast to many traditional wellbore simulators that account only for thermal conductivity in the reservoir, the developed simulator also considers convective heat transfer (by the movement of the fluids), making it applicable for lower completion zones. The proposed solution exhibits excellent stability and speed, which are usually the weak points of thermal reservoir simulators and provides engineers with an easy tool for modeling fluid and heat exchange between the near-wellbore reservoir region and a wellbore over time.