Efficient Hydrate Plug Prevention

A primary focus of flow assurance engineers during project development is the prevention and management of gas hydrate formation in pipelines. Historically, engineers have focused on hydrate formation prevention by injecting sufficient quantities of thermodynamic inhibitors to shift the hydrate stability region outside of the range of pressure and temperature operating conditions. However, as developments of hydrocarbon production occur in ever more extreme environments, the practice of complete prevention of hydrate formation may become prohibitively expensive because of the large amounts of inhibitor required. The example of high methanol dosage in equal volumes of inhibitor for water implies a cost of $84 per barrel of water produced at a methanol cost of $2/gallon. As the produced water volume increases during field life, the operators may not be able to pay for hydrate inhibition even with $100 per barrel of oil. The past decade has seen intensive research to discover strategies for transitioning from costly prevention measures to more cost-effective mitigation and flow-management measures. Such practices would allow for the possibility of hydrate formation in flow lines yet would involve managing the flow in the production system such that these formed hydrates would be continuously and safely transported along with the production fluids. This could reduce and, in some cases, eliminate the need for thermodynamic inhibition. Early attempts at moving from hydrate prevention to hydrate management focused on so-called low-dosage hydrate inhibitors (LDHIs), generally subdivided into kinetic hydrate inhibitors (KHIs) and anti-agglomerate chemicals (AAs). These chemicals could alter the formation rate of hydrates and/or limit the total growth while dispersing the hydrates in the hydrocarbon liquid phase. While these chemicals can aid in the management of hydrate formation, their range of application has typically been limited to a maximum water cut of less than 60%. More recently, researchers have sought methods to physically manage hydrate formation in a more holistic manner, focusing on the natural solids-carrying capability of the produced fluids and important interactions among any formed hydrates. These methods could be deployed if one had detailed knowledge of how blockages are formed and how fluid/emulsion properties affect hydrate transport. This presentation will discuss insights into the mechanisms of blockage formation through flow loop testing and accompanying simulations. It will also discuss how this knowledge has enhanced the ability of operators to successfully design production strategies to produce reservoir fluids in deepwater operations.