Abstract

Low Dosage Hydrate Inhibitors (LDHI's) have been actively investigated for well over a decade in both academia and industry. The promise of LDHI's has been to provide a viable alternative to thermodynamic inhibitors such as methanol and glycol. Inevitably, the journey of LDHI's from its modest beginnings in the minds and laboratories of researchers to a technically robust, operationally simple, and economically viable, alternative to conventional inhibitors has been fraught with challenges. In this paper, we discuss some of the drivers that led to the development of LDHI's for application in severe deepwater environments. The different classes of LDHI's are discussed briefly with an emphasis on the applicability window of each type of inhibitor. We also provide a detailed summary of the successful implementation of LDHI's in the deepwater and summarize key learnings obtained from the field deployment of this technology. We conclude by demonstrating the role of LDHI's in altering industry perspectives on hydrate control and their impact on the system selection and design of new field developments.

Introduction

Hydrate inhibition and control is often the basis of design for deepwater field developments. This is particularly true in deepwater environments such as the Gulf of Mexico and West Africa, where high reservoir pressures and low seabed temperatures provide a very high driving force for hydrate formation. Even in shallow water environments in the North Sea, it is common for hydrate management issues to dictate the system selection and topsides design. The cost of a hydrate blockage in a deepwater pipeline can be extremely high since a plug can take from days to months to dissociate. Localizing a hydrate blockage is also not trivial in long distance, and often buried, deepwater subsea flowlines, making hydrate plug remediation even more challenging. Consequently, extraordinary care is taken in the design and operation of deepwater systems to ensure that the system remains hydrate-free during normal steady state operation and during short-term and long-term shut-down of production.

Typically, gas pipelines are typically not insulated, and are operated with continuous injection of methanol or glycol. Oil pipelines are typically insulated, and hydrate inhibition is only required for transient operations such as start-up and shut-in/ re-start. During early field life, the water cuts are generally not very high, but they often rise very rapidly as the field matures. Consequently, delivery of the large volumes of methanol/glycol necessary to protect high volumes of water production becomes very challenging. Gas fields typically produce only condensed water in early field life, and they can be efficiently protected with continuous dosage of methanol or glycol. Formation water is typically not produced until mid or late life, and these volumes are generally not as high as those for high water cut oil fields. The industry has therefore based its hydrate control strategies on a combination of heat retention via pipeline insulation and inhibitor injection.

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