Bacterial diversity study applying novel molecular methods on halfdan produced waters

Nitrate has been added to the injection water in the Halfdan field since January 2001 in order to prevent reservoir souring. In early 2005, seawater breakthrough had occurred in four wells on Halfdan, and nitrate breakthrough was also detected. This resulted in a shift to nitrate utilizing bacteria in the produced water, confirming the impact of nitrate and the need to continuously monitor and optimize the treatment. In this paper we demonstrate that key bacterial populations can be identified by applying a range of novel molecular methods. Molecular techniques were implemented on water samples from Halfdan production wells producing with and without seawater breakthrough. For bacterial quantification, fluorescence in situ hybridization (FISH) was applied using a range of 8 hybridization probes. In order to describe the bacterial community composition in further detail a combination of molecular techniques was used. These techniques included polymerase chain reaction (PCR) followed by denaturing gradient gel electrophoresis (DGGE) and direct gene sequencing. In addition, gel retardation studies specifically targeting the genetic sequence coding for dissimilatory sulfite reduction [dsrAB) were conducted, thereby creating a fingerprint of both sulfate reducing Bacteria and sulfate reducing Archaea.