Field evidence indicates that the thermal regime in wellbore considerably affects the wellbore stability in directional and horizontal wells. However, the temperature effects have not been investigated thoroughly in existing literature, and the effects of drilling fluid flow and various heat sources on the behavior of formation temperature profiles during different operations are often neglected. The affected formation temperature in the vicinity of the wellbore could result in different formation rock behaviors and consequent wellbore stability problems. This study is conducted to examine the effect of temperature on the stability of the near wellbore region, taking into account the heat transfer between formation and flowing drilling fluid with the consideration of mechanical friction and associated heat sources.
A new model is proposed that is applicable to directional and horizontal wells. The model incorporates thermal effects due to the drag forces created from the contacts between drillpipe and casing/formation during drilling and tripping operations. It is then utilized in a number of configurations of directional wells to study temperature profiles behaviors and their effects on wellbore stability. It is observed that the drilling fluid temperature is noticeably under-predicted by existing literature, and in some cases it can easily exceed the geothermal formation temperature if mechanical friction is taken into account. The formation temperature profile near the borehole region is also found to be considerably affected when wellbore heat transfer is considered, as opposed to the constant wall temperature approach in existing literature. These differences alternate the temperature induced stresses and consequently change the mud weight window for wellbore stability prediction.
The proposed model and the results of this study are very useful for more accurate analyses of wellbore stability problems with a more detailed look into the effects of temperature. They can be used to enhance predictions of thermal regime in the wellbore at the design stage of well development or mud weight selection during drilling operation, thereby, avoiding potential drilling fluid/drillstring overheating and wellbore stability problems.