The souring of normally sweet production systems is a significant problem which can have implications to continued oilfield operations. Such problems are commonly approached by gathering of field sample and laboratory analysis or by simple test kits. This series in Hot Topics describes an alternative approach which includes the use of specialized field sampling and analysis procedures and portable equipment that can be moved from site to site. The current article provides an overview and introduction to how MIC growth can be studied and evaluated.
The souring of normally sweet production systems is a significant
problem. It can have implications in terms of
- reduced quality of produced hydrocarbons relative,
- the reduced productivity of wells,
- increased corrosivity of produced fluids.
In cases where remedial action is not taken, it can also have
implications relative to the potential for sulfide stress cracking
and selection of materials for downhole, flowlines and surface
facilities. Therefore, it is important to be able to properly
characterize field situations and make accurate recommendations
for remedial actions to minimize the impact of souring and to
prevent the occurrence of similar occurrences in other related
In an assessment of reservoir souring, field analysis provides
an important technical basis for engineering decision making through
their supporting scientific evidence. Such tests can yield information
useful in determining the sources and the potential severity of
souring and the selection and confirmation of successful remedial
actions. Some of the significant questions that can be addressed
through field investigation are indicated below:
- Is the souring a direct consequence of bacterial action?
- Were the bacteria introduced by the water injection system?
- Are the bacteria naturally occurring in the reservoir?
- Can the bacteria survive and grow under reservoir conditions?
- How adaptable are they to varying field conditions?
- Are there sufficient nutrients to sustain bacterial growth
in the system?
- What is the potential for controlling MIC and bacterial growth?
Field souring is often studied by either of two approaches:
- field sampling followed by transportation of the samples to
the laboratory for analysis, or
- analysis directly in the field using simplified field test
In many cases, the field sampling/laboratory approach is difficult
due to the remote nature of many onshore and offshore production
and injection facilities and the inability to transport, maintain
and analyze cultures. Additionally, most simple field tests lack
the sensitivity required to properly assess, characterize and
differentiate marginal cases.
Issues discussed in this series include:
- Description of MIC systems and methods of field investigation
- Specialized procedures and equipment for field or in-plant
investigation of souring, scaling, corrosion, fouling and bacterial
action in water handling systems. This includes a survey of planktonic
micro-organisms and bio-films as well as measurements of total
- A case study to validate this field testing capability
- Analysis of data obtained for characterization of reservoir
souring in petroleum production operations