Well integrity, perhaps a lesser known concept a few years ago but one which is definitely now at the forefront of operators’ minds, partially fuelled by the high profile Montara, Macondo and other high profile well control incidents.
Well integrity is determined from risk assessment.
Risk assessment comes in many facets, and is used in multiple industries. Within well engineering, risk assessment is conducted throughout every phase of the well’s lifecycle: from well planning (i.e. assessing the risk of setting casing shoe depths); to drilling (i.e. running drill pipe to ensure it is within trip margin); to completion (i.e. evaluating well control risk while running completion equipment) and production (i.e. managing annulus pressures). Risk assessment has rightly become a prominent area of focus within well engineering and is something that must be monitored throughout the lifecycle.
What comes to mind when trying to conduct a well integrity risk assessment for a producing well?
- Qualitative or Quantitative.
What is Qualitative Risk Assessment?
Qualitative risk assessment is the evaluation of both consequence and likelihood occurrence based on the judgement of the experienced personnel conducting the evaluation.
Using a hot coffee cup example, qualitative risk assessment is performed by drawing on the experience of the competent person’s understanding of the coffee cup’s quality. How likely it is to break, and what is the scale of potential consequence if the coffee is spilled.
From a well integrity perspective, the SW Well Assessment Integrity Tool is an evidence based, comprehensive review platform used to drive a forensic assessment of a candidate well that we used in house to perform qualitative risk assessment.
What is Quantitative Risk Assessment?
Quantitative risk assessment is the use of measurable objective data to calculate risk levels drawing reference from regulatory risk criteria.
Using again the hot coffee cup example, quantitative risk assessment can be performed by measuring the mechanical strength of the coffee cup handle. Taking reference from available material standards as guidance and ensuring that the handle is able to withstand the full weight of the coffee cup. Another example would be to measure the thermal insulation of the cup’s body resistivity to heat, to ensure that the user will not be burnt while holding the hot coffee.
From a well integrity perspective, SW’s well failure model can be utilised to assess quantitative risk. The well failure model is a barrier integrity assessment tool designed to take “Inputs” and pre- defined rules to generate the risk level of the relevant wells. Another approach would be the use of a risk based model as defined in ISO 16530-2, Well Integrity for the Operational Phase, where it is used to identify the magnitude of the risk presented by the failure of a single component and map this on a risk assessment matrix.
Which approach do I use?
Each method had its pros and cons but neither method is necessarily better than the other. The most appropriate approach instead will be dependent on the current available inputs and the desired results. The table below could be used as a guide to determine which risk assessment methodology to adopt for your next well integrity assessment.
The Final Word
Both forms of risk assessment can be used to monitor and maintain well integrity throughout the lifecycle and indeed a comprehensive risk assessment approach will involve a combination of the two. We hope we have shed some light into this subject and maybe the next time you are enjoying a hot cup of coffee you’ll think of qualitative and quantitative risk assessment (although you may wish to simply enjoy your coffee)
Please contact us to hear more about our well integrity capabilities or to be added to our quarterly well integrity and well control guidance notes.