Abstract

Microorganisms can cause numerous issues in oil field systems, including microbiologically influenced corrosion (MIC), reservoir souring, biofouling and separation problems. They are often controlled using biocides, however the dynamic nature of both oil field systems and microbial communities means that this is not a set up and leave solution. Therefore, rigorous biocide selection and microbial monitoring must be carried out in tandem to ensure that the treatment chemicals are effective from both a technical and cost point of view.

Microbial monitoring has advanced significantly in recent years, and now incorporates molecular DNA techniques such as quantitative polymerase chain reaction (qPCR) to quantify microorganisms, and metagenomics to identify them. These data however, still need relating back to the methods used to control microbial proliferation in oil field systems.

In this paper a combined approach is presented, with use of an onsite biocide evaluation test apparatus (BETA) to test up to sixteen biocides simultaneously at different dose rates and contact times for many repeated dosages. This is connected to a production or water injection system to realistically simulate pipeline conditions (e.g. temperature, pressure, flow rate, water chemistry, surface materials, etc.) during biocide evaluation. This allows for biocides to be techno-economically ranked under process conditions and may also be used to determine the effects of different biocide regimes on corrosion and pitting rates.

Any changes to the microbial community are detected early using the latest molecular microbiology techniques to ensure that the biocide maintains its effectiveness. This guarantees that any required biocide re-evaluation is carried out when needed, meaning that ineffective biocides are not needlessly dosed, which would increase operating expenditure (OPEX) costs and risks to asset integrity. It also avoids needless biocide re-evaluations where the current regime is working effectively.

An understanding of the type of data from different microbial monitoring tools is important and interpreting this correctly helps to bring a combined approach together, with some of the common pitfalls discussed. By using the most appropriate tools in the microbiologist's tool box for routine monitoring, along with a rigorous biocide evaluation regime, these advances can be used to keep a close control on OPEX along with improving asset integrity and increasing production.

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