Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 146
Avoiding gas Hydrate Problems in Offshore Drilling/Completion Operations
A. Chapoy, B. Tohidi
Drill Tech Asia, Kuala Lumpur, Malaysia, 27-28 November (2007)

A well-recognised hazard in offshore drilling/completion is the formation of gas hydrates in the event of a hydrocarbon flow into the wellbore from a reservoir. The pressure of the drilling fluid combined with relatively low seabed temperatures, can provide suitable thermodynamic conditions for the formation of gas hydrates in the event of a kick. This could potentially block the BOP stack, kill-lines and choke valves, obstruct the movement of the drill string, and cause serious operational and safety concerns. Currently, salts could be added to drilling fluids to inhibit hydrate formation in offshore and arctic drillings. With the drilling and production extending into progressively deeper waters (West of Africa, UK West of Shetland, and Gulf of Mexico), even saturated saline solutions may not provide the required protection unless combined with chemical inhibitors. The reported experimental data on gas hydrate formation in drilling fluids is very limited, and in some cases inconsistent. The available predictive methods are generally empirical correlations based on limited data and with limited application. 

The Centre for Gas hydrate has systematically study over the year the hydrate characteristics of the constituents of drilling and completion fluids by generating reliable experimental data for the most common salts, organic inhibitors as well as trademark chemicals currently used in drilling and completion fluids. These studies have been used to develop and extend the capabilities of a thermodynamic model, which can be employed to predict the hydrate free zone in drilling fluids designed for offshore and deepwater applications.

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