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Decommissioning of platforms and permanent plugging and abandonment (P&A) of oil and gas wells is a major future financial challenge for oil producing countries. This is especially true for offshore wells in deep water, where heavyduty drilling rigs with high day rates need to be applied for well closure. Even if well monitoring is typically not done after abandonment, this is an emerging topic – which is crucial to enable reuse of reservoirs for e.g., CO2 or hydrogen storage. With this respect, it is important to find new cost-efficient ways of monitoring plugged offshore wells, where in-situ gas measurements, satellite- and/or air- based monitoring techniques are difficult to implement or not possible. In the present paper, we propose the first steps for a data-based, geophysical monitoring strategy for permanently plugged wells. The foundation is a detailed analysis of documents provided by operators towards the Norwegian authorities. Based on these open-access data, we construct numerical wells and simulate/evaluate the geophysical response of the different well barrier materials. The data can be used for future field reuse/monitoring campaigns to detect missing or damaged cement barriers in abandoned oil and gas wells. This will broaden the available sites for future large-scale CO2 storage.

In this paper we ask the question whether or not electrochemically enhanced deposition of minerals can be utilized to repair leakage paths existing in cement plugs in wells. Electrical polarization of two electrodes may result in oxygen reduction and water electrolysis, where both processes change the local pH close to the two electrodes. The solution close to the anode is becoming acidic while close to the cathode it is becoming alkaline. Since solubility of many scaling minerals is pH dependent, precipitation of minerals on conductive surfaces can be induced by electrical polarization. We test whether cathodic polarization of conductive surfaces can be used to facilitate deposition of minerals from brines resembling reservoir fluids. As a model the reservoir formation water from the Gyda field was chosen. The electrochemically enhanced deposition at 23 and 120 °C from a synthetic Gyda brine was tested by polarizing at 5 V. The results show that cathodic polarization significantly enhanced precipitation of minerals from the synthetic Gyda brine.

In this study, our recent and new approach for detailed tracking of the interface between well fluid and cement by using particles is investigated. The particles can enable us to know the precise location of the interface between two fluids and be sure about displacement efficiency in the annulus. This includes the introduction of intermediate buoyant particles that reside at the interfaces between successive fluids in a well (e.g., cement-spacer or spacer-mud). Such particles must overcome strong secondary flows to travel with the interface. For this purpose, the displacement mechanisms of Newtonian and non-Newtonian fluids in the annulus of vertical and inclined wells is investigated by using an experimental set-up with concentric and eccentric annular geometries. For more efficient displacement, the displacing fluid should have a higher density than the displaced fluid, and the intermediate-buoyancy particles that reside at the interface between successive fluids are introduced into the models. Particle motions are investigated in models with different fluid rheology and displacement flow rates. This approach for tracking of the interface can improve the quality of annular cementing of CO2 wells and thus the storage safety.