Øystein Arild at ONS August 31th. Photo: IRIS

Risk of leakage as measurement for quality in P&A solutions


By using leakage risk as a quality measure, P&A barrier solutions could be faster, cheaper and better, Øystein Arild stated during a technical session at ONS August 31th.

The technical session focused on permanently Plug and Abandonment (P&A) of wells, and in his presentation "Plug and abandonment: Quality at the right price" Arild emphasised what is meant by quality in a P&A setting, and how can it be measured.

Quality in permanent P&A
Quality in permanent P&A settings can be measured through leakage risk including two aspects: probability of barrier failure and leakage rate. Failure probability is the percentage chance that a well will leak within a given time period, and can be assessed by a combination of failure modelling and degradation modelling of barrier elements.

To quantify leakage rates to seabed (given that a barrier system fails), these steps can be applied: identifying the relevant failure mode, identify leakage drivers (pressure, buoyancy), choose a representative flow model and consider leakage reduction effects.

Quality at the right price
In DrillWell tests on permanently plugging of wells have been carried out.
- If the cement in annulus isn't weakened or of bad quality, a cement plug can be placed inside the casing.

The challenge is to determine whether the annulus cement is good or not. To make the decision one can evaluate logging measurements, then estimating leakage potential and assessing leakage risk.

Further efforts needed
In order to achieve quality at the right price, we need to know more about how cement sealing capability relates to the log response. Arild ended the presentation by referring to a barrier evaluation facility which is under construction at IRIS.

- The purpose is to use logs to predict "leakage rate" based on the log response and connect this to the risk-based quality measure  to support a decision on using the existing cement or not.

Read more about P&A research at IRIS.
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