TetrakisHydroxyMethylPhosphonium Sulfate (THPS) is used as a bactericide in the Skjold/Gorm oil production systems in the Danish sector of the North Sea. A reduction in H2S generation downhole due to THPS treatment resulted in savings on H2S scavenger consumption. In addition, use of THPS provides other benefits which are discussed in the paper. THPS treatments are compared with conventional bactericidal treatments and it is demonstrated how downhole injection of THPS retards the growth rate of Sulfate Reducing Bacteria (SRB) and the rate of H2S production. THPS treatment resulted in a change in the downhole bacterial population, evidenced by changes in the sulfur isotope ratio of the produced H2S. Re-injection of produced water with low H2S concentrations increases the potential for iron sulfide (FeS) deposition,
both in topsides and downhole. THPS changes both the physical form and the bacterial content of the FeS deposits. Removal of the deposits with acid is facilitated by TI-IPS which exhibits FeS dissolving capabilities. Field tests have verified the effect.