A New Subsea Station for Deep Gas Treatment Allowing to Maximize Subsea Gas Fields Production

Abstract

Abstract The offshore oil & gas industry is presently interested in exploring and developing ultra-deep gas fields for which the water depth is higher than 1,500 m. Considering the water depth and the characteristics of these reservoirs, the exploitation of such fields represents a challenge. To unlock these reserves, it is necessary to tackle obstacles like lack of available pressure, risk of solid deposits (hydrate, wax), and liquid accumulations in low points of the exports line(s). To cope with these issues when the field architecture is not sufficiently flexible (for example, if the number of export lines is limited), one solution is to remove the liquids before production in gas line. SUBGAS has been developed as a potential solution to these challenges and can be implemented over a wide range of application cases. SUBGAS is a subsea station that performs gas/liquid high performance low temperature separation (LTS), allowing gas dewpointing to be performed in subsea conditions. This subsea processing station performs a liquids and condensable components removal from the production gas coming from wells. The treated gas leaving the station is exported alone in the export line(s) while the liquids and condensable components are exported to shore via a dedicated line. Due to the dewpointing operation, the pressure drops in the export gas line(s) are reduced, hydrate and/or wax formation risk is avoided or significantly reduced, and the operability of the line is improved as there is no or a very low amount of liquid. Based on numerical studies, a technical comparison with typical gas/liquid (G/L) separation, subsea compression, and other dew-pointing technologies is presented to highlight advantages of the proposed solution. Then, the SUBGAS station process and design is highlighted through a specific study case. An assessment of the Technology Readiness Level (TRL), according to API 17N, of the solution has been also done showing a high level of maturity allowing a rapid time to market. By performing a gas treatment to remove liquids and condensable components, SUBGAS subsea station proposes an innovative solution to improve gas fields production via long subsea tie backs. Due to its simple process, high robustness, high maturity level, and considering the possibility to be used for brownfield long tie-back development, SUBGAS can be one of the keys allowing to maximize gas fields productions in the coming years.