Objective

As life extension projects see many oil wells being used beyond their design life, ensuring the structural integrity of critical components to prevent unexpected failures has become more important than ever.

ASPIRE aims to deliver results to the operator in terms of risk, as the product of probability and consequence of failure. This provides the company with inspection recommendations based on the strength response of the corroded conductors. Based on risk information, the company can then decide whether the conductor requires repair or is taken out of service. Through this comprehensive approach to structural integrity assessment, the operator’s cost of inspection will be substantially reduced.

Background

The ASPIRE components that are being integrated in a decision support integrity management tool for upstream assets are illustrated in Figure 2. There are four of them:

• Risk-based Inspection (RBI) is a methodology for identification of high risk scenarios by review of active/potential damage mechanisms and the suitability of mitigation methods. RBI allows inspection/maintenance resources to be optimised. The challenge is that a standard approach cannot be adopted here as the complexity of equipment may not allow for this to take place. The solution could develop in the form of a software package that uses the fundamentals of probabilistic approach and can easily be customised to include limit state equations for any particular damage type as well as different consequence scenarios.
• Total Quality Inspection (TQI) covers: selection of the most appropriate non-destructive testing (NDT) technique, qualification of equipment, procedures and inspection personnel, and data recording and interpretation. TQI offered by Innospection and TWI as partners is based on NDT research undertaken over the past 25 years. The project partners – Innospection and TWI - continue developing new inspection techniques and tools for inspection and rating them by their performance for specific inspection tasks;
• Fitness for Service (FFS) may allow for a detailed assessment of flaws using built-in Finite Element Analysis (FEA) capabilities following advanced inspection as offered by Innospection to evaluate complicated geometries and loadings. TWI has been involved in developing ECA/ FFS/ FFP procedures for 50 years and provides assessments in accordance with BS 7910 and API 579. TWI also offers a range of standard FFS software packages (CrackWISE, IntegriWISE, WeldCRO) for corrosion, fatigue, fracture and creep assessments;
• Optimum Repair Technologies (ORT) provide operators with the means to establish the most cost-effective approach to reclaiming a damaged component. Through TWI expertise in weld repair, cladding, surfacing, coatings etc., the project partners are able to advise independently on all remediation techniques, e.g. replacement, modification or material upgrade.

Our Approach

The initial, high-level screening is based on a conservative effective area calculation and corrosion rate (CR) estimation, which establishes a remaining life (RL) for each conductor. An appropriate fitness for service (FFS) approach will be selected for each conductor, depending on whether it is subjected to global bending, compressive loading, or a combination of the two. This assessment is facilitated by a stability check, based on international standards, of the well conductors.

The operator establishes risk targets (using ASPIRE) to determine the risk (probability of failure) target, with the remaining time to that target considered as the risk-based RL (as shown in Figure 1). This determines the point at which an inspection is recommended to be carried out to better quantify the damage state.

ASPIRE is also capable of performing the conductor assessment with the inclusion of any imperfections, even when the RL at the assessment target date was greater than zero.

ASPIRE then carries out a risk assessment to consider the likelihood (with limit state equation as the second moment of inertia) and consequence of failure.