Hydrate control during deep water drilling : Overview and new drilling fluids formulations

Gas hydrate formation during deep-water offshore drilling is a well-recognized operational hazard. Plugging the BOP stack, choke and kill lines with hydrates can cause a serious well control problem. We conducted an up-to-date review of the drilling practices and mud formulations applied in deep water drilling as related to gas hydrates control and mitigation. The review indicated that Salt/polymer mud systems are the most commonly used mud formulations in the Gulf of Mexico, North Sea and offshore Brazil. Drilling with these systems has been successfully achieved to water depths of up to 7500 ft (2287 m). In the second part of this work, we measured the hydrate phase equilibrium of 25 drilling fluid formulations. The testing also included two new spotting fluids formulations. The testing results indicated that, on weight basis, NaCI is the best thermodynamic inhibitor among the salts tested in this work, which are NaBr, Na-Formate, KCI, and CaCl 2 . Although the high solubility of the Na-Formate makes it possible to increase the hydrate suppression beyond that of NaCI, the former is less effective on weight basis than NaCI. The glycols are considerably less effective inhibitors, on weight basis, than the salts. However, greater degree of suppression can be achieved by using mixtures of salts and glycols. Among the tested glycols, ethylene glycol showed the best performance compared to AQUA-COL TM S, GEO-MEG TM D207, and HF-100N TM .