Selection of the Appropriate H2S Scavenger Chemistry Based on the Mineral Scaling Risk

The study concerns a non-conventional field in the Middle East, where gas contains 4 mol% of H2S and 3 mol% of CO2. Gas is exported and production water is reinjected in the aquifer. The first target is to have H2S level in the injected water around 400 ppm and the second target is to have H2S level in the injected water lower than 60 ppm. Quantity of water to be treated will be around 10 000 bbl/d for the first weeks and decreasing up-to few 100s bbl/d after some months. The objective of this paper is (i) the evaluation of the scaling risk; (ii) identification of suitable H2S scavengers and (iii) assessment of the effect of H2S scavengers on the calcite scale due to the increase of pH. The scaling risk assessment has been performed with the help of a commercial scaling risk evaluation software. The scaling risk has been evaluated from well producer downhole to surface facilities. The precipitable masses of scales have been calculated. The identification of suitable H2S scavengers has been based on (i) assets feedbacks, (ii) feedback from TotalEnergies headquarter laboratory tests results, (iii) H2S scavenger chemistries based on literature review and (iv) Chemical suppliers’ recommendations; (v) Assessment of the effect of H2S scavengers on the CaCO3 scale. The cost performance analysis has also been carried out. The scaling risk assessment has shown at the wellhead, for early life production, in order to prevent both calcite and barite scales, the temperatures should be between 140°C and 120°C. If the temperature is equal to 150°C, a moderate risk of calcite is predicted. For late life production, if the temperature is equal to 100°C, moderate risks of both calcite and barite. At the 1st stage separator and flare KO drum, if temperatures are equal to 150°C and 140°C, a high risk of calcite is predicted. The suitable scale inhibitor has been selected with the help of dynamic tube blocking tests in the laboratory. The synthesis of TotalEnergies laboratory tests results, affiliate and partner site feedback and literature review and according to the performance, reactivity, compatibility with water, increase of scale and impact of scale inhibitor performance, Glyoxal is the best in class followed by Methylene Bis-Oxazolidine (MBO), then the MEA triazine, then Hemiacetal, then Ethylenedioxy Dimethanol (EDDM) and finally 2-Ethyl Zinc Salt. Field test has successfully shown that the Glyoxal H2S Scavenger has an excellent performance with no increase of calcite precipitation.