Thermal wellbore strengthening through managed temperature drilling - Part II: Chemical system design and laboratory testing

The coated exothermic particles, which were based on the hygroscopic calcium and magnesium salts with chlorine and bromine, were designed such that they could release their “payload” via an extended time-release mechanism, to ensure that the heat release reaches the appropriate target location in the wellbore at exactly the right time. The chemical candidate systems were found to effectively heat up the wellbore and increase temperature up to 90 °C. This, in turn, will elevate the fracture gradient by several hundred psi, depending on formation properties. The particles need to be transported to the target formation and their reaction products need to be carried away from the target formation by a suitable carrier fluid that can handle the exothermic dissolution of a large amount of salt without any instability. Details regarding the formulation and testing of non-coated and coated particles and their carrier fluid are discussed here, as well as considerations for field application of thermal wellbore strengthening. The developed managed temperature drilling technique, enabled by the chemical system described here, can be used to minimize lost circulation events and associated well trouble time and cost during drilling, cementing and completion operations.