Selection of an Active Souring Management Solution for a Gulf of Mexico Waterflood

This paper presents an overview of the factors involved in the selection of an active souring management solution for the Mars field, at which waterflood operations are due to commence in March 2004. It is well documented that the majority of similar seawater injection applications have experienced increased down-hole sulfate-reducing bacteria activity and the reservoir souring and H2S control difficulties associated with this. The Mars field was initially commissioned in 1996 with non-NACE MR0175 compliant materials used for well tubing and casing. Following detailed reservoir modeling, and HSE Risk Assessment, a plan was developed to change-out all production tubing to NACE materials, and a 100 % redundant H2S monitoring system was installed. However, replacement of production casing materials was cost prohibitive so a plan was developed to mitigate the predicted levels of souring by the use of an active souring control approach. Investigation into the various alternatives available, including sulfate removal membranes, biocide treatment and nitrate or nitrite injection, has determined that nitrate injection is likely to be the most effective souring prevention tool.