Emulsion-Stabilized Hydrate Slurries: An Operational Flow Assurance Reality or a False Sense of Security

Abstract

Summary In this paper, we provide a detailed case study on a laboratory-to-field strategy evaluating the use of flowline emulsions as a method of chemical-free hydrate control up to 25 vol% water cut. This is now ready to be put into successful operational practice in the deepwater production environment. The oil in question was known to have a strong tendency to emulsify, and a detailed study of the separability of oil and water was necessary to understand the propensity for emulsions to form and, more importantly, break. Rheology studies were used to determine the thermal and shear influences on emulsion stability. These results better aligned the hydrate application testing performed using rocking cell and autoclave methods to determine hydrate formation under dynamic conditions and the propensity for hydrates to form at ever-increasing water cuts. Customized test protocols were required for the hydrate testing to better risk manage the nuanced aspects of hydrate formation, including agglomeration amount and bedding (settling) propensity. The emulsion testing showed a very stable and tight water-in-oil (W/O) emulsion formed that did not invert until >50 vol% water cut. The emulsions were rheologically complex and very temperature and shear dependent. At typical steady-state subsea conditions, significant separation was not anticipated to occur up to and beyond 25 vol% water cut. Hydrate performance testing was able to demonstrate that at shear stresses approximating the flowline, 25 vol% water cut was able to remain emulsified for the whole of the test and was not available to create a significant hydrate slurry. At 30 vol% water cut, significant hydrates formed and were deemed too operationally risky to go untreated. As of the time of this writing, the field is not producing significant amounts of water requiring hydrate control; however, the testing enabled a risk management approach that will require no hydrate control (“do nothing”) for water cuts below 25 vol% for extended shutdowns and cold restart scenarios. Flow assurance strategies and procedures are being updated to reflect this approach. Taking advantage of the use of naturally occurring emulsions to solve deepwater hydrate flow assurance challenges is a novel and developing technique. Successfully risk-managed cases are required to be shared with the industry to drive toward a lower carbon footprint production future coupled with less chemical exposure to the environment.