Successful LDHI Qualification for Produced Fluids in a Flexible Riser at 10oF (SS-FA)

Abstract

A new subsea tieback in the Gulf of Mexico (GoM) is expected to experience temperatures as low as 10 o F in the system due to high levels of expansion cooling. The system will operate within the hydrate region, at a high degree of sub-cooling. Current test methods used to select and determine the effectiveness of Low Dosage Hydrate Inhibitors (LDHIs) are capable of evaluating at temperatures down to 39 o F. A new test method was developed to effectively evaluate the performance of LDHIs at temperatures as low as approximately 10 o F.The flowline for the subsea tieback is un-insulated and the flexible riser is partially insulated by the layers in the construction of the pipe. The fluids will experience expansion cooling due to the Joule-Thomson effect as they move up the riser and will not be able to adequately take advantage of the "warm" surrounding seawater. As a result, the lowest expected temperature in the system is 10 o F. This lower temperature also means a higher degree of sub-cooling. Typically, the higher the subcooling, the higher the dose rate required to inhibit hydrates using an LDHI. To date, there is no data supporting antiagglomerate low dosage hydrate inhibitors (AA-LDHIs) are effective with black oils at operating temperatures between 10 o F and 30 o F. A new test method was required to show that an AA-LDHI will effectively inhibit hydrates at the system conditions of the subsea tieback.A description of the new test method used to evaluate AA-LDHIs at temperatures below 39 o F will be presented as well as the results. The results include the evaluation of produced fluids with and without the addition of AA-LDHI. These results demonstrate that hydrate formation and the effectiveness of AA-LDHI to inhibit hydrate blockage can be detected at low temperatures using the new test method. It is shown that the AA-LDHI effectively inhibits hydrate blockage at approximately 10 o F. It is also demonstrated that the mixture of produced water and AA-LDHI will not freeze at system temperatures.