Thermal modeling for calculation of formation temperatures for deep water wells with chemical heat source

Incedalip, Oguz
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Drilling through depleted zones is becoming more common as the resources are exhausted and the fields mature. To be able to access deeper sections of the reservoirs, it is essential to drill through depleted zones effectively. This need brings around the challenges including severe lost circulation and poor zonal isolation. Artificially strengthening the wellbore is of crucial importance in order to achieve successful drilling as well as cementing for deep water wells. Altering the thermal stresses results in increased tangential stresses in the vicinity of the wellbore and therefore increases the fracture gradient. Thermal stresses can be increased through a controlled exothermic chemical reaction of certain salts which are coated via pharmaceutical techniques to delay the reaction until the carrier fluid transports the materials to the target zone. This approach with its innovative method surpasses other methods like downhole heaters as it is more practically feasible. The technique has a great potential to decrease mud losses, hence to decrease non-productive cost and time. In this study a computational thermal model is developed in order to calculate the temperature distribution of the formation as well as the annular and tubular fluids for given heat generation rates. The numerical model which uses finite volume techniques is developed for an axisymmetric cylindrical geometry including the drilling fluid, casing, annulus, and formation for transient heat transfer including a time and location dependent heat generation source. The results are analyzed in comparison to one analytical solution as well as a commercial software package, Drill Bench, in order to verify the accuracy of the model for scenarios with no heat generation, since modelling of heat generation is not available for the other approaches. Some parameters of the model such as the heat transfer coefficient are calibrated in order to achieve the best agreement between different analyses. Heat generation rates are obtained for different chemical compounds tested in insulated calorimeter experiments. The results of different heat generation rates for different heat generation durations as well other problem parameters such as circulation rate are investigated. In addition, thermal stress calculations based on the temperature increase are also presented.