Evaluation of Methods and Quality Barriers in Plug and Abandonment - Technology Advances, Physical and Governing Requirements
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Improving the present P&A operation with respect to costs and safety is of current interest to the petroleum industry. This is because this operation will frequently be performed in the future due to the large number of drilled wells. Due to this, it is an increased interest in providing and ensuring the long-term integrity in the well since this is critical for the success of an abandoned well. This requires a good understanding of the integrity in the well, and models, methods and technologies to understand, determine and ensure this integrity are crucial for improving the operation. This thesis will investigate one of the most fundamental parts of the P&A operation, which is to ensure a sufficient barrier in the well. On request from AF Offshore Decom AS, the thesis will look into challenges with the present P&A of old wells where little or no integrity information is available. In addition, the possibility for solving these challenges and at the same time save costs will be investigated. Specifically, investigate if there are significant savings in a scenario where technology development allows logging through multiple strings. The thesis evaluates the annular integrity in depth by using a finite-element method model of the permanent formation-cement-casing barrier. In addition to these physical requirements, the regulatory requirements are taken into account when searching for improvements in the P&A operation. Furthermore, the present methods to evaluate the cement in the well are investigated, which includes acoustic logging. Limitations are identified, and the opportunity to use technologies and methods from other industries to evaluate the annular cement is studied. This includes technologies as computed tomography, magnetic resonance imaging, and the use of drill and borescope. Lastly, possibilities to improve the P&A procedure itself, and make it independent of the logging methods are investigated. For instance, removing the strings more efficiently by using undeveloped methods such as laser or corrosion. Based on the research in this thesis, it is not unlikely that technology advances and new methods will make the present issues with logging irrelevant. Be aware that the recommendations suggested in this thesis are only meant as guidelines and where to go further. Developing and improving this area are a large task, and solving one challenge often results in another challenge. However, it includes huge opportunities for the right ideas. At the moment, there is no best practice, there is only better practice.