Evaluation of the Elevated Temperature Performance and Degradation Mechanisms of Thread Compounds

Thread compounds play an important role in the sealing ability of casing connections in the oil and gas industry. Next to their lubricating role during assembly, most of these thread compounds make use of nonbiodegradable or persistent particle additives to aid in the sealing ability. Soon, these additives need to be replaced by benign alternatives as agreed in the proceedings of the Oslo-Paris Commission. This is, however, a challenge in high temperature (>150°C) well environments. This paper presents an investigation of the high temperature failure mechanisms of thread compounds with the aim to develop biodegradable high temperature resistant thread compounds. To this end, the performance of commercially available, environmentally acceptable thread compounds was investigated with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), high temperature rheometry and high temperature pin-on-disc experiments. The compounds are assessed on their stability, consistency, lubricity, and the resulting wear at high temperature. The results indicated that, without exception the commercially available thread compounds investigated in this study fail by adhesive and/or abrasive wear at around 150 degrees Celsius because of thermally induced degradation. To remedy this and to validate the mechanisms, a prototype thread compound was developed which exhibits strong film forming. The conclusion is that a successful high temperature resistant environmentally acceptable thread compound can likely be developed. The key property of this thread compound should be the ability to form a tribofilm during make-up which protects the surface at a later stage when the lubricant has lost its consistency and the base oil is fully evaporated.