Assessing Well-Integrity Risk: A Qualitative Model

Abstract

For successful delivery of well integrity (WI), there needs to be an understanding of the risks that can cause undesirable events such as safety hazards or loss of containment. Performing a risk assessment (RA) on a well, or type of well, will help determine and rank the potential risks and provide information that allows limited resources to be applied in the most effective manner. The main objectives of performing a risk assessment include (a) following a formal process to assess risk consistently and to enable comparison between well-barrier failure-mode scenarios; (b) qualitatively assessing well-barrier failure risk for every segment of a well; (c) documenting suggestions that are offered by the riskassessment team for mitigating well-barrier failure risk; and (d) providing a report of the methodology, failure-mode scenarios, risk ranking, and potential mitigation actions for use as a reference tool for managing WI on a routine basis.Our WI/RA model follows a common qualitative risk-assessment process-a team-based, structured brainstorming format, using the "What-If Methodology" to identify potential hazards associated with well-barrier failure modes. In addition, the model has the following attributes:It incorporates a unique method to segment well barriers into discrete sections, successively "failing" each section for evaluation. The list of analyzed well-barrier failure modes, along with their risk ranking, becomes the risk register for the well or type of well.It is adaptable for assessing well-barrier failure modes on a single well, or a group of wells, having the same general design parameters. An entire well portfolio can be assessed quickly by analyzing types of wells rather than individual wells.It can be used to assess well-barrier failure risk for any type of well.The model can easily be modified to conform to any company's risk model.The WI/RA model has been proven to Successfully assess well-barrier failure risk for thousands of wells Focus specifically on well-barrier failure modes, and as a result be an effective tool that should be incorporated into a "bestin-class" WI program Be used as a management tool to provide guidance for how limited resources can be used effectively to continuously deliver WI.

The Risk of Using Risk Matrices

“…Thus, they considered blowout and well control to have the same degree of risk. Poedjono et al (2009) and Dethlefs and Chastain (2012) also documented the use of RMs in a drilling context, but they used the more common practice of multiplying the probability and consequence scores to obtain a "risk score" for each outcome. Table 2 shows the results of applying this procedure to the Pritchard et al (2010) example.…”

How to Design Rating Schemes of Risk Matrices: A Sequential Updating Approach

“…Risk matrices are easy to implement and can be implemented even where data are limited. Therefore, they have become popular decision-support tools in both the public and private sectors, (3)(4)(5)(6) in areas such as well-integrity risk, (7) drilling hazard management, (8) climatic change responses, (9) and so on. However, despite its simplicity and wide usage, recent research has revealed several flaws in the risk matrix.…”

“…(16) However, when risk matrices are used to prioritize several risks, risk matrices should have a higher resolution to better differentiate all the risks. (3,7,8,15,19) As a result, when we design the rating scheme of a risk matrix, the method we use should work as well as possible regardless of the various inclinations for resolution.…”

Design and Analysis of Leak-Testing Methodology for Gas Lift Valves

“…They cited several reasons for GLV failures, including flow cutting in sealing seats caused by well unloading of completion fluids, the valve-spring fatigue failure, damage during installation, erosion during multiphase or wet gas injection, and damage to valve seat caused by chattering in a low-pressure-drop situation. Gilbertson et al (2013) developed a thermally actuated GLV for offshore wells to add redundancy to well systems and significantly to increase well safety. This valve avoids the use of either active control or passive pressure-induced actuation that is performed in current valve systems.…”