Experimental and modeling study of salt precipitation during injection of CO 2 contaminated with H 2 S into depleted gas fields in the Northeast of the Netherlands

• Published in: SPE Journal
• Main Authors: Bolourinejad, P., Herber, R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: Carbonic acid
• Online Access: https://hdl.handle.net/11370/0faf17e7-998b-4af8-b271-a3d4512684f2; https://research.rug.nl/en/publications/0faf17e7-998b-4af8-b271-a3d4512684f2; https://doi.org/10.2118/164932-PA; http://www.scopus.com/inward/record.url?scp=84919442254&partnerID=8YFLogxK

Depleted gas fields are among the most probable candidates for subsurface storage of carbon dioxide (CO 2 ). With proven reservoir and qualified seal, these fields have retained gas over geological time scales. However, unlike methane, injection of CO 2 changes the pH of the brine because of the formation of carbonic acid. Subsequent dissolution/precipitation of minerals changes the porosity/permeability of reservoir and caprock. Thus, for adequate, safe, and effective CO 2 storage, the subsurface system needs to be fully understood. An important aspect for subsurface storage of CO 2 is purity of this gas, which influences risk and cost of the process. To investigate the effects of CO 2 plus impurities in a real case example, we have carried out medium-term (30-day) laboratory experiments (300 bar, 100°C) on reservoir and caprock core samples from gas fields in the northeast of the Netherlands. In addition, we attempted to determine the maximum allowable concentration of one of the possible impurities in the CO 2 stream [hydrogen sulfide (H 2 S)] in these fields. The injected gases - CO 2 , CO 2 +100 ppm H 2 S, and CO 2 + 5,000 ppm H 2 S - were reacting with core samples and brine (81 g/L Na + , 173 g/L Cl - , 22 g/L Ca + , 23 g/L Mg + , 1.5 g/L K + , and 0.2 g/L SO 2- 4 ). Before and after the experiments, the core samples were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD) for mineralogical variations. The permeability of the samples was also measured. After the experiments, dissolution of feldspars, carbonates, and kaolinite was observed as expected. In addition, we observed fresh precipitation of kaolinite. However, two significant results were obtained when adding H 2 S to the CO 2 stream. First, we observed precipitation of sulfate minerals (anhydrite and pyrite). This differs from results after pure CO 2 injection, where dissolution of anhydrite was dominant in the samples. Second, severe salt precipitation took place in the presence of H 2 S. This is mainly caused by the ...