Wellbore Heat Transfer Model for Wax Deposition in Permafrost Region

Abstract

Producing waxy oil in arctic area may cause wax deposited on the well wall. Since wax deposition is strongly thermal related, accurate heat transfer model is necessary in predicting and preventing wax depostion. A mathematical model was derived based on energy balances for heat exchange between the producing fluids and production string as well as the formation/permafrost. To simplify the calculation, oil and gas were assumed well mixed as one single-phase in the tubing. Furthermore, Singh's model for wax deposition was coupled with the heat transfer model. Wax concentration and effective diameter were updated with time in the temperature calculation. Pressure distribution was calculated over time to check whether the reservoir energy was sufficient to produce the oil during the production process. Besides, a user friendly GUI was developed by VB and MATLAB to run the simulation. The effects of permafrost, thermal insulation, well geometry and wax deposition on the heat transfer calculation were studied. Simulation results illustrated insulating the wellbore and evacuating the production casing annulus effectively reduced the wellbore heat loss. The model can be used in the temperature prediction of an injection well or production well in permafrost region or non-permafrost region.