Calcium nitrate, a fertiliser component, is being used by Statoil in its Gullfaks reservoir to cut the need for environmentally-harmful chemicals to prevent hydrogen sulphide formation.
Applied on the North Sea field for more than three years, this solution eliminates the toxic and corrosive pollutant in order to meet sales specifications for gas exports.
Injecting seawater to maintain reservoir pressure on Gullfaks encourages the growth of the bacteria which in turn create hydrogen sulphide.
Statoil has previously combated this process by injecting biocides to kill the bacteria.
“Calcium nitrate has replaced an annual consumption of 240,000 litres of biocide,” explains Tore Thorstenson, discipline leader for production chemicals.
“In addition, we have been able to reduce the use of other environmentally-harmful chemicals by 1,000-2,000 tonnes per annum.”
Statoil has been a prime mover in developing the technology, which has been adopted on Gullfaks for the first time.
This work was headed by Egil Sunde, one of the group’s specialists, in cooperation with Norsk Hydro and the University of Bergen.
Earlier research in the USA on increasing dosages failed to yield useable results, Mr Thorstenson explains. So achieving a good effect with low doses represents a breakthrough.
Biocides were also replaced during the research programme with calcium nitrate on Statoil’s Veslefrikk field in the North Sea to reduce corrosion in piping systems.
The same was done on the Statfjord field operated by the group last autumn, and Statoil is considering adoption of the system on other fields.
In addition to the positive environmental gain at lower cost, this solution is also positive for the working environment of offshore personnel involved in chemical dosing.
They no longer have to suffer an unpleasant odour or run the risk of direct skin contact with the biocides, which pose a health hazard.
Using calcium nitrate to curb hydrogen sulphide formation marks an important step forward in developing environment-friendly solutions and eliminating hazardous chemicals.
Statoil is well on its way to achieving zero harmful discharges on its oil and gas fields by 2005, as required by the Norwegian authorities.