HYDRATES—A CHALLENGE IN FLOW ASSURANCE FOR OIL AND GAS PRODUCTION IN DEEP AND ULTRA-DEEP WATER

Abstract

Offshore exploration and production is going to deep and ultra deep waters, driven by the depletion of continental shelf reserves and the high demand for hydrocarbons. This move requires the continued extension of existing technologies and the development of new technologies that will make the investment economically viable. Innovative flow assurance technology is needed to support ultra deepwater production, particularly within the concept of platform free fields where there is a need to minimise interventions.

Hydrates present one of the major challenges in flow assurance. Deep and ultra deep water operations together with long tiebacks present the ideal conditions for the formation of hydrates which can result in pipeline blockage and serious operational and safety concerns. Methods to combat hydrates range between control and management. One main technique has been to produce the hydrocarbons outside of the thermodynamic stability domain of hydrates. This is achieved by keeping the temperature of the hydrocarbon above the stability temperature of hydrates by insulating the pipe line, or by introducing heat to the hydrocarbon. Another efficient way of combating hydrates has been to shift the hydrate phase boundary to lower temperatures by using chemicals like methanol and mono ethylene glycol (MEO) which are known as thermodynamic inhibitors. Within the last decade a new generation of hydrate inhibitors called low dosage hydrate inhibitors (LDHI) has been introduced. One type of these LDHI are kinetic hydrate inhibitors (KHI) that, when used in small concentrations, slow down hydrate growth by increasing the induction time for their formation and preventing the start of the rapid growth stage. Another approach to managing hydrates has been to allow them to form in a controlled manner and transport the hydrate-hydrocarbon slurry in the production pipe. In this paper we describe the various approaches used to combat hydrates to ensure flow assurance and we discuss the cons and pros of every approach and the technology gaps.