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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. more...

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. more...

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. more...

The technology risk aversion among decision makers in the oil and gas industry leads to over-cautious technology decisions. To enable an acceleration of technology development and adoption on the Norwegian Continental Shelf, the need for new ways to measure innovation performance are escalating. This thesis assessed various approaches to R&D performance measurement, and identified some key characteristics of a project level measurement system which is both theoretically sound and practically useful. Further, the thesis examined performance measurement in industrial R&D, by use of a survey of the DEMO2000 program portfolio. The R&D projects had set a broad range of project specific goals, which were generally suitable for fostering both project excellence and creative freedom. Even though goals who supported customer interactions and collaborations were to some degree lacking. The performance measurements used by the projects seems to fail compared to what the literatures conceders as ‘highly effective’. The actual usage of the measurement output is decisive for the effectiveness of performance measurement. However, only 30% of the projects assess their KPIs within the frequency which in the literature is considered to be sufficient (monthly). To better understand the entire technology value proposition of a new product development, the R&D project needs to build strong relations between researcher, developers, and customers, with a multi-disciplinary approach. This interplay both can and should be measured by KPIs, to ensures the project is delivering according to plan (business process perspective) and asking the right questions to the right people (customer perspective). However, currently, only a handful of the survey respondents seem to capture these important aspects in their performance measurement procedures. A holistic performance measurement system, which captures both the potential value proposition and the project progress, while the right competence is involved, is considered to make innovation teams thrive. However, the lack of effective measurement systems in the DEMO2000 projects, may increase the risk of the ‘wrong’ products being built. In that case, optimizing the product will not yield significant results. more...

Large-scale implementation of carbon dioxide (CO2) sequestration in depleted oil and gas reservoirs may potentially mitigate global climate change. However, successful CO2 storage is contingent on a limited leakage through abandoned wells, which are commonly sealed with Portland cement. Thus, with the purpose of assessing depleted oil and gas reservoirs as sites for CO2 sequestration, it is of interest to evaluate the degradation of Portland cement when subjected to CO2 at reservoir conditions. In this study, in-situ synchrotron micro computed tomography (µ-CT) images of Portland G cement exposed to CO2-saturated water at high pressure and temperature have been analyzed with the aim of obtaining an enhanced understanding of the cement carbonation process. The cement sample had a through-going cavity that served as an idealized CO2 leakage pathway during the µ-CT experiment, and alternating nonflow and constant flow conditions of CO2-saturated water were applied. Automatic procedures have been developed to segment and further analyze the digital three-dimensional images. The results showed that in-situ µ-CT with synchrotron radiation is an experimental technique well-suited for gaining insight into the dynamics of cement carbonation. The µ-CT images revealed processes occurring in the cement sample in the course of the experiment. Cement reaction zones were seen to develop near CO2--cement interfaces, and the growth rate of reacted cement was found to be faster for CO2 flow compared to static conditions. Moreover, the results suggested that the growth of reacted cement slows down with time given constant CO2 conditions. The images showed that crystals of calcium carbonate precipitated in the CO2 leakage path during the first period of static CO2 conditions. During time intervals of CO2 flow, on the other hand, the crystals re-dissolved. The volumetric dissolution rate was approximately linear as function of time for constant CO2 flow conditions, and it was found to increase when the CO2 flow rate was raised. Furthermore, the measurements indicated that the cement sample experienced a slight expansion in the course of the experiment. The obtained results seem promising for the integrity of CO2 wells in the case of static CO2 conditions, attributed to the slow cement carbonation and the cavity self-healing observed. However, the results suggest a relatively fast cement degradation and re-opening of cavities for cement exposed to CO2 at a constant flow rate, which indicates that the sealing ability of wells may become compromised if well cement is exposed to a rapid CO2 flow over time. more...

Carbon Capture and Storage (CCS) projects are aimed to store CO2 underground and to prohibit/restrict any leakage to the well, formation and to the surface. Standards applied to control a well and to keep its integrity are aimed to stop this fluid entrance. Nevertheless, leakage can occur from the debonded formation cement interfaces. The main goal in this experimental work was to study leakage of CO2 along cement formation interface. In order to investigate debonding degree, samples were prepared as a small well model with a cement/formation interface. During sample preparations 4 rock, 2 cement and 3 fluid types were used to see appearance of weak bonds. 24 different samples were scanned with µ-CT and modeled with Avizo to see interface porosity and morphology. Scanned samples had been tested in CO2 batch exposure to visualize chemical alterations on the samples. Setup had been made for CO2 core flooding to measure the amount of fluid leaked through the cement-formation interface. Result before experiments showed that porous and permeable rocks with good mud/cake fluid coverage give lower bonding degree while pristine samples (model of ideally cleaned well) give 100% bonding percentage. In addition from the µ-CT results it was found that the samples treated with filter cake had higher bonding degree than the samples treated with mud. After the flooding/batch exposure experiments degradation has been observed on the cement and rock surfaces. Meanwhile CO2 and brine cleaned cement-rock interface from mud/cake on core flooding experiments. Moreover, the amount of fluid leaked through the debonding was measured and compared for three rock samples. more...

This experimental work is the continuation of the literature study of cement-formation bonding, done in the autumn semester. Cement-formation bonding has not been given special attention so far, in resolving the well integrity problems. A lot of work has been done on other influential factors but this area has not been studied much. With a view to have better understanding about this unexplored area, the experimental setup was developed and several experiments were carried out. Although some experiments were done previously on this topic but that work was limited to two specific rock types. Four different rock types, including sandstone, limestone, chalk and shale were used in experiments. The results obtained from these experiments are discussed in this report. The rock samples were also treated with the drilling fluid to observe the effect of drilling fluids on the bonding strength at cement-formation interface. These results were, then compared to the dry samples of the same rock type and difference between bonding strength was measured. This research work will be helpful in understanding the failure occurred at the cement-formation interface. By knowing all these facts affecting the bond strength, it is possible to improve the bonding strength by treating them carefully. Future work in this area can be valuable to overcome the well integrity issues. more...

The number of well integrity issues increase in the petroleum industry as wells are exposed to severe downhole conditions and have longer lifetimes. Techniques for enhanced oil recovery, like steam injection and field development in the Arctic, expose downhole materials to harsh cyclic temperature variations. This is also the scenario for normal production situations, although not to the same extent. Production can be stopped for various technical or non-technical reasons, or for injection purposes, all of which influence the temperature in a well. Heating and cooling make the steel casing expand and contract as a result of thermal expansion. This volumetric change can influence downhole well barriers, e.g. annular cement sheaths leading them to fail. Failure of annular cement sheaths can introduce well integrity issues and subsequent well leakages of downhole formation fluids. An experimental set-up was build during the present work to investigate the effect of thermal cycling on annular cement sheath integrity. The set-up included all the three materials in a well, casing, cement and rock allowing the whole system to be tested in one assembly at the laboratory scale. The testing specimens are composed of steel pipe cemented in place in a confining rock, thereby representing a downscaled wellbore. Temperature variations were applied radially to the casing and the effect of these variations on cement sheath integrity were observed. In-situ well integrity was continuously monitored by means of Acoustic Emission Testing (AET), and post failure analysis was conducted by Computed Tomography (CT) investigations. Three specimens were tested during the present work: The first sample was not exposed to any thermal cycles ("virgin" sample), and was directly sent to CT investigation after cement curing. The second sample was cemented with a centralized casing and the third was cemented with casing 50% off position. Both of the latter samples were exposed to the same thermal cycle profile.The experimental results from the continuous in-situ AET measurements revealed that casing centralization is important for wellbore integrity and that thinner annular cement sheaths withstand less temperature variations. CT examination and 3D visualization confirmed severe debonding at the casing-cement interface, for all the three specimens, including the uncycled "virgin" specimen. This indicates that the casing-cement bond is generally weak. For the cement-formation interface, the debonding was particularly clear for the two thermally cycled specimens. Furthermore, the 3D visualization results based on CT-scans displayed that, debonding is more prominent than radial cracking. Calculations of interfacial porosity, defined as the volume of interface pores/cracks as a fraction of the total sample volume, revealed that thermal cycling and casing centralization affects the magnitude of debonding and cracking of cement. The "50% casing stand-off" sample showed most interfacial porosity (1.38%), followed by "centralized casing" sample (1.18%) and finally, uncycled "virgin" sample showed, least interfacial porosity (0.59%). This displays that thermal cycling does indeed affect the sealing ability of annular cement sheaths in a negative way.Future work is essential in order to fully understand within which temperature ranges a particular well can be operated, without leaks along the annular cement sheaths. This can be obtained by conducting tests varying the different materials. Experiments with different cement systems, various formations and casing surface finishes can be executed. In addition, experimental tests determining the effect of exposing the formation to drilling fluids prior to cementing and further thermal cycling can be conducted. Effect of various wellbore scaling ratios is also important, as the effect of the material curvatures and total volumes on the obtained results are unknown. more...