Hydrogen sulphide (H2S) is naturally occurring in many oil and gas production streams. H2S scavengers are used as additives to reduce the concentration of H2S gas in order to meet export gas/crude specification or for mechanical integrity requirement. Most Total installations today use conventional chemicals such as monomethyl amine (MMA) and monoethanolamine (MEA) triazines for H2S removal. According to Total affiliates, deposit formations have been observed when triazine based scavengers are used. In this paper alternative chemistries for H2S scavenging are assessed. Six H2S scavengers have been evaluated, these are: Methylene bis-Oxazolidine (MBO), Ehylenedioxy Dimethanol (EDDM), 2-Ethyl Zinc Salt, Glyoxal, Hemiacetal and MEA Triazine. For the evaluation of H2S scavenger's efficiency, an experimental method has been developed.
For the selection of H2S scavengers, the following tests have been carried out: (i) evaluation of H2S scavenger efficiency in the oil and gas phase and (ii) production chemical compatibility test. The three-best performing H2S scavengers have been analysed for (i) the impact of H2S scavenger on foaming; (ii) impact of H2S scavenger on emulsion; (iii) compatibility between H2S scavenger and production water; (iv) effect of H2S on the scale inhibitor efficiency; (v) effect of H2S on the corrosion inhibitor efficiency.
Laboratory tests have shown that the three best H2S scavengers, based on the performance test, are Zinc 2-ethylhexanoate, Methylene bis-Oxazolidine (MBO) and Triazine. Methylene bis-Ozaxolidine tested on North Sea site in the multiphase and gas phase has shown preliminary good results. No impact on emulsion, foaming and corrosion were observed from the three-best H2S scavengers selected. Test performed on site with zinc-based product showed very good performance on H2S removal but impacted produced water quality. The zinc-based product formed deposits when mixed with production water therefore this H2S scavenger should not be used for scavenging H2S in the water phase. Though Triazine and MBO based scavengers increase water pH, potential scaling issues can be mitigated by scale inhibitor, however dithiazine deposits formed with the use of triazine based scavengers limits its use for H2S scavenging in oil gas installations.
An experimental method has been developed for the evaluation of H2S scavengers. Alternative scavenger chemistries have been identified. These chemistries reduce the risk of deposit formation in the H2S removal process during oil and gas production.