RESERVOIR SOURING CASE HISTORY
CAPCIS carried out a predictive study for an onshore development that had been in operation for 17 years and was pressure-supported by aquifer water flood. The formation water was of high salinity, therefore a high level of dilution was required before microbiological activity could occur; this was responsible in part for a long delay in the onset of souring. The objectives of the study were to identify appropriate control options and the cost implications of the possible alternatives.
A field specific souring prediction was carried out using the
CAPCIS model, which enabled the creation of well-specific
H2S production profiles, together with a predicted field
aggregate.
A review of the materials and facilities showed that
the main problems arising from the souring would be
generation of sour gas for use in the power plant. Materials
risks due to cracking were found to be low. Therefore,
control options focused on the use of chemical treatment
options rather than materials replacement.
The options to achieve this were:
- Biocide / nitrate injection at waterflood outlet
- Injection at the plant inlet manifold
- Injection into the gas phase at the separator outlet
The potential costs of the different options were compared. In this specific case, the use of biocides offered significant potential cost saving over scavengers, depending upon the type of product used. However, there were concerns over the success of biocides in this field in the long term. The next most cost effective approach was the use of scavengers injected into the gas phase, which offered a cost saving of approximately 30% in comparison to treating the total fluids at the plant inlet. In the later field life the additional chemical cost due to souring was predicted to increase to approximately $305,000 (in 2005 terms).
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