Mercury Scavenging from Multiphase Flow Via Chemical Injection

Summary In the oil and gas industry, elemental mercury (Hg0) is typically removed from gas streams by adsorption beds known as mercury removal units (MRUs). However, there are instances where it is desirable to scavenge Hg0 earlier in the process. The objective of this study was to conduct laboratory experiments to evaluate several chemical injection–type concepts for the removal of Hg0 from multiphase flow. This included elemental sulfur dissolved in toluene, premade particles with CuS as active species and a class of H2S scavengers that function by forming metal sulfides [iron sulfide (FeS), zinc sulfide (ZnS), or copper sulfide (CuS)] upon contact with sour gas. All methods remove mercury by forming solid mercury sulfide (HgS) or similar compounds. Laboratory tests were performed by measuring outlet Hg0 in a gas phase (inlet Hg0 of ca 50 µg/Sm3) flowing through a flask containing an aqueous phase and n-octane at ambient conditions. Toluene with dissolved sulfur was ineffective in scavenging mercury from the gas phase under ambient conditions. In contrast, a copper-based H2S scavenger efficiently removed Hg0 and is viewed as a promising candidate for upscaling to practical applications. Removal via CuS/HgS is, however, not suitable for fields with water discharge to sea but viewed as most interesting for fields with produced water reinjection (PWRI). After reaction with sulfide, the formed CuS particle dispersion was found to cause very little injectivity impairment in corefloods, better than or comparable to quartz particles of small sizes (<5 µm). A concept with CuS coated onto magnetite (Fe3O4) particles was also investigated and showed significant efficacy as a removal method for Hg0. These particles were also verified to be efficiently retained in a magnetic filter medium. This concept is, from a practical use perspective, much more complex than injection of the copper-based H2S scavenger chemical but principally offers a route to control/remove the solids.