Continuous Application of Anti-Agglomerant LDHI for Gas-Condensate Subsea Tieback Wells in Deepwater Gulf of Mexico

摘要

The formation of natural gas hydrates continues to be a common flow assurance challenge, particularly in deepwaterrnproduction systems. When water and natural gas are present in an environment of cold temperatures and high pressures,rnhydrates can form causing partial or complete blockage of production. Prevention of hydrate blockages via chemicalrninhibition is typically accomplished by using either thermodynamic inhibitors (methanol, ethylene glycol) or Low DosagernHydrate Inhibitors (LDHIs).rnThe production system described herein consists of four subsea gas wells (2,200 feet water depth) tied back via 19-milerndual flowlines to the host platform. Hydrate control is required due to the condensed water from the gas entering the hydraternforming region within a few hundred feet of the wells and continuing through 19 miles of uninsulated flowline to the platform.rnThe production system was designed and engineered for the use of LDHI for hydrate control to avoid the large volumes ofrnmethanol would be required both in early field life (condensed water) and later field life (formation water).rnField conditions dictated (Kelland 2010, Patel and Russum 2010) the use of an Anti-Agglomerant (AA) LDHI versus arnKinetic Hydrate Inhibitor (KHI) due to the high subcooling, low water cut, and performance with long shut-ins on a longrnsubsea tieback. However, there were several challenges to conventional AA chemistries presented by this application. Somernof these challenges included treating condensed water in condensate, high gas-to-oil ratio (GOR), rapid cooldown of fluids,rncontinuous injection and impact on topsides fluid processing. As such, a new AA chemistry was developed to perform underrnthe expected field conditions for all stages of the field life.rnOverall, there were several critical steps to the successful development and deployment of a new AA for use withrncondensed water on gas-condensate deepwater production system. Herein, we describe the project design and development,rnthe chemical design, testing, and planning done before start-up, the transition from methanol treatment to LDHI, and therngeneral results and lessons learned to date for this project. This project represents one of the few uses (Klomp et al. 2004) ofrncontinuous AA to treat condensed water in a long gas-condensate tieback in deepwater.