| Popis: |
Tanks used to store produced water on Floating, Production, Storage and Offloading units (FPSOs) are extremely susceptible for generation of high hydrogen sulfide (H2S) levels due to the activity of sulfate-reducing bacteria (SRB). The FPSOs operated by Petrobras in the Campos Basin, offshore Brazil, all contain slop water tanks, while some also have upstream oil-water separation tankage. Slop water, comprised of produced water, ballast water from oil cargo ships and deck water, contains SRB and their nutrients required for generating H2S. Additionally, solids accumulations at the tank bottoms provide an excellent environment for microbial growth. A 2002 field trial on an FPSO confirmed the viability of combined batch treatments of anthraquinone and of a THPS blend to control H2S biogeneration better than previous treatment programs. Anthraquinone, a non-toxic SRB inhibitor, and THPS, an oilfield biocide, act synergistically to effectively control the H2S biogeneration in this environment. The combined chemical treatment strategy has now been implemented successfully on six Petrobras FPSOs. Flexibility has been important in developing the treatment programs since operating parameters are different for each FPSO and change due to increased water production rates. Options include the ability to inject the chemicals continuously or batchwise at different locations and to alter the volumes and ratios of chemicals for optimizing control over H2S and corrosion. This paper describes the individual FPSO water flow and storage systems and discusses the customized chemical treatment programs. Included are field H2S data showing the progression of the programs as they are being continually adjusted to optimize H2S generation and cost effectiveness. Also included are results of laboratory microbial studies showing the synergy of anthraquinone and THPS and of corrosion studies which have impacted the direction of usage of these chemicals. With over 100 FPSOs operating worldwide, the described treatment program can significantly affect the safety and environmental aspects of processing water containing SRB. |
