March 1994
2nd International Conference on Chemistry in Industry
Kingdom of Bahrain
Paper-030
Conference Paper
On-site Evaluation of Organic Biocides for Cost-Effective Control of Sessile Bacteria and Microbially Influenced Corrosion
Microbially influenced corrosion (MIC) is a well known and severe problem in oilfield water injection systems. In order to reduce the effects of MIC, organic biocides are commonly added as slug doses to control the growth of bacteria (particularly sulphate-reducing bacteria (SRB)) in biofilms on pipe wall surfaces. Tests were undertaken on biofilms developed in a purpose-built Biocide Evaluation Test Rig (BETR), which was connected downstream of the deaerator towers on the Upper Zakum water injection system, which is operated by the Zakum Development Company, offshore Abu Dhabi. The BETR was shut-in throughout any system biocide treatments. During an initial biofouling period, a thick, black biofilm was formed, which contained high numbers of SRB and other bacteria, both aerobic and anaerobic. MIC pitting of carbon steel studs in the BETR was observed, confirming that MIC is a risk if bacteria are not effectively controlled.
Significant differences were found in the biocidal performance of the ten chemicals tested, despite each chemical having been tested by the vendors in their laboratories. These differences are due to the different active ingredients used and the blending of the products. In addition, synergistic effects were sometimes noted, with the different biocide chemistries enhancing the overall performance of the biocide package. Such differences between the various biocides confirms the need to conduct such tests on-site under system conditions: the use of an ineffective biocide can lead to corrosion, injection well plugging and reservoir souring problems. In the case of the Upper Zakum system, the continuation of the treatment regime selected from the field evaluation has maintained a microbiologically clean system and minimised maintenance costs.
