Sulfate Reduction Activity – MIC

Measure sulfate reduction rates in samples

In nearly all industries, sulfate reducing bacteria (SRB) are routinely implicated in microbiologically influenced corrosion (MIC).

In the oil and gas industry, biological sulfate reduction has severe consequences in addition to MIC including reservoir souring, contamination of natural gas and oil, and reservoir plugging potentially leading to reduced oil production.

The Sulfate Reduction Activity assay is similar to a tracer study and provides an estimate of the in situ sulfate reduction rate. In the laboratory, a small amount of 35S-sulfate is added to the sample and incubated at temperatures close to observed under field conditions. After a short incubation period, reduced inorganic sulfides are extracted, 35S-sulfides are measured, and sulfate reduction rates are calculated. The sulfate reduction assay is sensitive and accurate even in system with high background sulfate concentrations.

How does it work?

Samples (water, solids) are collected and shipped overnight on ice (4°C). In the laboratory, 35S is added. Samples are incubated under conditions mimicking those in the field. Sulfate reduction will produce H2S which can precipitate with reduced iron that may be present. After incubation, any iron sulfides formed are recovered and total H2S is volatilized and trapped.

How do I use the results?

Compare sulfate reduction rates between samples to:

  • Conclusively determine if biocide treatment was effective against SRB activity
  • Pinpoint areas of active sulfate reduction
  • Optimize SRB control measures
  • See back for examples

Other Frequently Asked Questions

  1. How do I submit a sample?

Submitting a sample for sulfate reduction activity is no more difficult than collecting a sample for chemical analyses.

  1. Concerns about radioactivity?

The 35S sulfate is added to the sample in the laboratory, not in the field.

  1. How are the results reported?

Sulfate reduction activity results are reported as rates in units of mmoles/L/day.

  1. What about qPCR and QuantArray?

The sulfate reduction activity assay is a great compliment to qPCR and QuantArray quantification of sulfate reducing bacteria and archaea.

How do I use the results?

The detection of 35S sulfides indicates sulfate reduction activity and therefore the potential for MIC or souring due to the activity of sulfate reducing bacteria or archaea. While a quantitative assay, data interpretation should emphasize comparisons between carefully selected sample locations or time points to isolate variables and answer specific questions as highlighted in the following example.

Is sulfate reduction occurring in the system?  If so, where should I focus control efforts?

In this example, samples were collected from five locations in the system and submitted for quantification of sulfate reduction activity (Figure 1).

  • Although lower at sample location 5, sulfate reduction activity was detected at all sample locations indicating the potential for MIC throughout the system.
  • Sulfate reduction rates were relatively high particularly at sample locations 2 and 4. MIC at these locations may be a more immediate concern and control efforts should be considered.
  • Based upon the detection of sulfate reduction activity and other system monitoring results, a biocide treatment was performed.

Was the biocide effective?

A second round of samples were obtained from the same five system locations following the biocide treatment. Sulfate reductive activity following treatment was compared to the pre-treatment results to assess the effectiveness of the biocide (Figure 2).

  • Overall, the biocide appeared to be effective – sulfate reduction activity was substantially lower at almost all sample locations following treatment.
  • The notable exception was sample location 4 where sulfate reduction activity remained relatively high despite biocide treatment.
  • Further investigation would be warranted to determine effective control measures at this location.