Decarbonisation Technology - November 2024 Issue

reservoirs? Tracer technology offers a valuable solution to this debate, as it can be effectively employed across various types of CCUS projects, regardless of the chosen storage method. In this article, we discuss two projects where tracer technology was applied successfully in different types of reservoirs. K12-B gas field Tracer technology has been applied in the K12-B gas field on the Dutch continental shelf to advance our understanding of CO 2 storage and migration. This allows us to better appreciate its role in optimising CCUS efforts and ensuring the long-term integrity of CO₂ storage. Background The K12-B gas field, situated about 150km (about 93.21 mi) northwest of Amsterdam in the Dutch North Sea, has been central to research on CO₂ injection and storage. The project aims to evaluate the feasibility of injecting and storing CO₂ in depleted natural gas fields on the Dutch continental shelf towards developing a permanent CO₂ injection facility. This mature field has been producing natural gas since 1987. Traditionally, the CO₂ separated from this gas was vented into the atmosphere, but recent efforts have redirected it into the same reservoir from which it originated, at a depth of around 4,000 metres (about 2.49 mi). The initiative at K12-B is part of the Dutch government’s CRUST project, which aims to evaluate the feasibility of CO₂ injection in depleted natural gas fields and assess the associated environmental and legal aspects. This project, subsidised by the Dutch Ministry of Economic Affairs and operated by Gaz de France Production Nederland B.V., represents a pioneering effort in offshore CO₂ storage. Challenge The integration of CO₂ storage into existing gas fields presents several challenges. There are inherent uncertainties surrounding the long-term behaviour of CO₂, the effectiveness of enhanced gas recovery (EGR), and the potential environmental impacts of such storage solutions. Specifically, the challenge lies in accurately assessing the behaviour of injected CO₂, understanding its migration pathways, and

ensuring that it remains securely stored without unintended leakage. In this depleted gas reservoir nearing the end of its life, the objective was to track the movement of CO₂ and enhance the understanding of the reservoir’s behaviour. The study revealed that CO₂ exhibited similar behaviour to methane in certain areas of the reservoir but diverged significantly in other regions. This discrepancy introduced uncertainties, even though this mature reservoir was well-understood. Solution During the analysis of CO₂ breakthrough, tracer data was used in conjunction with analogue equipment from the well. CO₂ was injected into the same field from which it originated, with the aim of enhancing gas recovery while the field remained in production. A CO₂ tracer was incorporated to optimise the injection scheme and successfully identify the breakthrough of re-injected CO₂. The tracers served multiple purposes: ○ Tracking CO₂ migration: By following the path of the tracers, the movement of CO₂ through the reservoir could be accurately mapped. This included measuring the CO₂ injection rate, composition, and the physical interaction between injection and production wells. ○ Assessing reservoir behaviour: Tracer data helped evaluate the sweep efficiency of the injected CO₂ and the overall flow behaviour within the reservoir. ○ Ensuring well integrity: The tracers also provided insights into the condition of the CO₂ injection tubing and the quality of the cement bond in the injection well. Results The application of RESMAN’s tracer technology at K12-B yielded valuable insights into the CO₂ storage process. Tracers detected the CO₂ as soon as it broke through, whereas traditional gauges did not register any change for months. The analogue equipment, with its lower resolution, detected the breakthrough with a delay compared to the tracers. This immediate detection by tracers provided a much clearer and more timely resolution of the CO₂ movement, highlighting the superior sensitivity and effectiveness of tracer technology in monitoring such processes.