THERMAL MODELING OF DRILLING INTO STEAM CHAMBERS

On occasion SAGD wells need to be drilled into or close to steam chambers. When drilling such wells the drilling fluid temperature may become excessively high, endangering personnel and exceeding the borehole stability, bottom hole assembly or drilling fluid temperature limitations. The drilling was simulated to predict the resulting wellbore, mud return, and formation temperatures. The transient thermodynamic model was created with commercial software, calibrated by matching predicted temperatures with actual drilling data from several cold wells. The calibrated model was used to predict the formation temperature of several hot wells. The wellbore temperature during the drilling of several generic wells was also evaluated. This model may be used to ensure the mud temperatures are not prohibitively high during future drilling operations. The mud return temperature was predicted to within B11B0C of the actual. The formation temperature was predicted to approximately B120B0C when drilling into wells with formations of 50 to 200B0C. The generic drilling scenarios modeled demonstrate that it is possible for the mud to return to surface at temperatures exceeding 100B0C resulting in the water component of the mud flashing to steam. When entering a hot wellbore, tripping in slowly while circulating may be required to avoid returning excessively high temperature mud to surface. Mud coolers may be required to prevent the mud temperature from climbing too high. A small number of SAGD wells have been drilled into steam chambers. The model allows this limited experience to be expanded. The model may be used for planning of future drilling operations by predicting mud temperatures in a variety of drilling scenarios especially with regards to safety concerns. In addition the need for employment of mud coolers or specific trip procedures can be evaluated. The approximate accuracy of the simulation software employed is also demonstrated.