Tor Bjørnstad

• Dugstad, Øyvind & Bjørnstad, Tor (2026). Isotopic exchange of tritium (³H) and¹⁴C in gas/liquid systems. Applied Radiation and Isotopes. ISSN 0969-8043. 230. doi: 10.1016/j.apradiso.2026.112428. Full text in Research Archive
• Silva, Mario; Stray, Helge; Metidji, Mahmoud Ould & Bjørnstad, Tor (2021). Variation of the partition coefficient of phase-partitioning compounds between hydrocarbon and aqueous phases: an experimental study. Fuel. ISSN 0016-2361. 300. doi: 10.1016/j.fuel.2021.120915. Full text in Research Archive Show summary

  Many non-ionic chemical compounds will form real solutions in equilibrium between two immiscible phases in contact. The partition coefficient (K) is defined as the quotient between the equilibrium concentration of the substance in the hydrocarbon and the aqueous phase. The reversible partition of a compound between hydrocarbon and aqueous phases is the basis of the partitioning inter-well tracer test (PITT). PITTs are of high interest for the characterization of oil reservoirs, in hydrogeology for assessment of the contamination of soils by non-aqueous phase liquids (NAPLs), and in process technology. The K value of substance is influenced by the actual chemical and physical conditions of the system where it will be used as phase-partitioning tracer. Thus, it is important to evaluate the extent of variation that the K value can exhibit under different relevant conditions. In the present document, we report the methodology and findings from the experimental determination of the K values of 4-methoxybenzyl alcohol, 3,4-dimethoxybenzyl alcohol, 4-chlorobenzyl alcohol, 2,6-dichlorobenzyl alcohol, pyridine, 2,3-dimethylpyrazine and 2,6-dimethylpyrazine between different hydrocarbon and aqueous phases. These 7 compounds were previously identified as interesting PITT tracer candidates. Individual K-values were determined under different temperatures, compositions of the hydrocarbon phase (synthetic mixtures of toluene, isooctane, and 1-octanol and 5 real crude oils), and different ionic strengths (I) and ionic compositions of the aqueous phase. The reversibility of the partitioning phenomena was also evaluated. The composition of the hydrocarbon phase and the ionic strength of the water phase were found to influence the K values of all seven compounds. Results suggest that the substitution of monovalent ions with divalent ions in the aqueous phase, keeping the ionic strength constant, does not influence the K values. Temperature effects on the K-values are always visible for 3,4-dimethoxybenzyl alcohol, 2,6-dichlorobenzyl alcohol, pyridine, 2,3-dimethylpyrazine and 2,6-dimethylpyrazine. Dependent on the hydrocarbon phase composition, temperature also influences the K-values for 4-methoxybenzyl alcohol and 4-chlorobenzyl alcohol.

• Bjørnstad, Tor (2021). Modern Industry: Neutron Basic Interactions, Sources and Detectors for Materials Testing and Inspection. In Greenspan, Ehud (Eds.), Encyclopedia of Nuclear Energy. Elsevier. ISSN 9780128197257. p. 372–391. doi: 10.1016/B978-0-12-819725-7.00087-8. Full text in Research Archive
• Bjørnstad, Tor (2021). Modern Industry: Application of Neutrons for Materials Testing and Inspection. In Greenspan, Ehud (Eds.), Encyclopedia of Nuclear Energy. Elsevier. ISSN 9780128197257. p. 392–420. doi: 10.1016/B978-0-12-819725-7.00088-X. Full text in Research Archive
• Bjørnstad, Tor (2021). Modern Industry: Gamma Methods for Materials Testing and Inspection. In Greenspan, Ehud (Eds.), Encyclopedia of Nuclear Energy. Elsevier. ISSN 9780128197257. p. 345–371. doi: 10.1016/B978-0-12-819725-7.00142-2. Full text in Research Archive
• Arun, Panneer Selvam; Metidji, Mahmoud Ould; Silva, Mario; Krivokapic, Alexander & Bjørnstad, Tor (2020). Thermo-Sensitive Nanogels for Targeted Tracer Release in Push and Pull Operations. In Behm, Edward (Eds.), SPE Improved Oil Recovery Conference 2020. Society of Petroleum Engineers. ISSN 9781613997055. doi: 10.2118/200446-MS. Full text in Research Archive
• Silva, Mario & Bjørnstad, Tor (2020). Determination of phase-partitioning tracer candidates in production waters from oilfields based on solid-phase microextraction followed by gas chromatography-tandem mass spectrometry. Journal of Chromatography A. ISSN 0021-9673. 1629. doi: 10.1016/j.chroma.2020.461508. Full text in Research Archive Show summary

  In the present document, we report the development of an analytical method consisting of a sequential direct-immersion/headspace solid-phase microextraction (DI-HS-SPME) followed by gas-phase chromatography and tandem mass spectrometry (GC-MS/MS) for simultaneous analysis of 4-chlorobenzyl alcohol, 2,6-dichlorobenzyl alcohol, 4-methoxybenzyl alcohol, 3,4-dimethoxybenzyl alcohol, pyridine, and 2,3-dimethylpyrazine in oilfield production waters. These compounds are under evaluation for use as phase-partitioning tracers in oil reservoirs. To the best of our knowledge, this is the first time SPME has been applied to the analysis of these compounds in production waters, or any other type of matrix where the compounds targeted are the base for a technical application. Relevant extraction parameters, such as the adsorbent phase of the fiber, direct immersion or headspace, addition of salt, temperature and time of extraction were investigated. The final optimal operation conditions consist on extracting 5 mL of sample at pH 9.0 with 1.8 g of NaCl with constant stirring during 5 minutes of DI-SPME followed by 15 minutes of HS-SPME at 70 °C using a DVB/CAR/PDMS (50/30 µm) fiber. The limits of quantification (LOQ), linearity, precision and accuracy of the method were evaluated. Analyses of the tracer compounds and recovery studies were also performed on production waters from 8 different oilfields of the Norwegian continental shelf. LOQs between 0.080 and 0.35 µg L−1 were obtained. The recovery yields of the method were consistently higher than 85% and RSDs less than 13%. None of the tracer compounds was found in the real samples processed, which is consistent with one of the requirements for an artificial tracer in an oilfield: absence or constant and low background in the traced fluid. The performance of the method developed, combined with its easiness to automate, introduce a new, accurate and cost-efficient technique to process the hundreds of samples required by an inter-well tracer test.

• Selvam, Arun Kumar Panneer; Metidji, Mahmoud Ould; Silva, Mario; Krivokapic, Alexander & Bjørnstad, Thor (2020). Thermo-Sensitive Nanogels for Targeted Tracer Release in Push and Pull Operations. In Behm, Edward (Eds.), SPE Improved Oil Recovery Conference 2020. Society of Petroleum Engineers. ISSN 9781613997055. doi: 10.2118/200446-MS. Full text in Research Archive Show summary

  The single-well chemical tracer test (SWCTT) is widely used in the determination of residual oil saturation (SOR) in the near-well region. SWCTTs typically require large amounts of chemicals and some days of well shut-down. In the present paper, we propose using thermo-sensitive nanogel carriers for targeted release of tracers for SWCTTs. This approach has the potential to significantly reduce the time and amount of chemicals required by a SWCTT. The targeted tracer release method was inspired by previously developed drug delivery applications using stimuli-sensitive nano-capsules. Nanoparticles loaded with medical cargo were synthesised to target specific sites. The release of the active principles would then be triggered by an in-situ (temperature, pH) or ex-situ (magnetic field, light) stimuli. A novative approach to address the current limitation of classical SWCTT is based on the biomedical background. It consists in using a poly-N-isopropylacrylamide (pNIPAm) based nanogel, known for its thermo-sensitive nature, to ensure the in-situ delivery of tracer molecules. This effect is explored as a mechanism to both load and release the tracers for a SWCTT. PNIPAm nanogels or hydrogels are highly hydrophilic, cross-linked polymeric networks. When the temperature of the solution is increased above the lower critical solution temperature (LCST) of PNIPAm molecule, the capsules exhibit a reversible collapse effect, causing the release of the tracer molecules. The hydrodynamic diameters of capsules were measured using Dynamic Light Scattering (DLS) and were found to be 195 nm at 25 °C and 73 nm at 45 °C. The nanogels exhibit a reduction in volume to 8 times when the temperature is increased from 25 °C to 45 °C. This change in volume acts as a lock-in mechanism once the tracer is loaded and open-up to release loaded tracers. The study of the encapsulation and release of tracer compounds was achieved using passive and partitioning tracers loaded into the structures. The capsules showed a significant tracer loading efficiency. For studying the release rate and mechanism, increase in temperature was used to trigger the release of tracers. Although the SWCTTs are the most used tracer tests by the oil industry, their development have been relatively slow since it was originally introduced in 1973 (Deans 1971). The present study aims at presenting a novel approach on how nanotechnology can be used to reduce the large amounts of chemicals and time required by classical SWCTTs. Concepts and results about the synthesis of the nano-carriers, loading and releasing of the tracers are presented and discussed.

• Silva, Mario; Metidji, Mahmoud Ould; Stray, Helge & Bjørnstad, Tor (2019). Alkylpyrazines - from the “Dinner Table” to the Oilfield: A New Class of Partitioning Tracers, IOR 2019 – 20th European Symposium on Improved Oil Recovery. European Association of Geoscientists and Engineers (EAGE). ISSN 9789462822788. doi: 10.3997/2214-4609.201900063. Full text in Research Archive
• Metidji, Mahmoud Ould; Silva, Mario; Krivokapic, Alexander & Bjørnstad, Tor (2019). Synthesis and Characterization of a Reactive Fluorescent Tracer and its Possible Use for Reservoir Temperature's Data Collection, IOR 2019 – 20th European Symposium on Improved Oil Recovery. European Association of Geoscientists and Engineers (EAGE). ISSN 9789462822788. doi: 10.3997/2214-4609.201900062. Full text in Research Archive
• Silva, Mario; Stray, Helge & Bjørnstad, Tor (2019). Stability assessment of PITT tracer candidate compounds – The case of pyrazines. Journal of Petroleum Science and Engineering. ISSN 0920-4105. 182. doi: 10.1016/j.petrol.2019.106269. Full text in Research Archive
• Silva, Mario; Stray, Helge & Bjørnstad, Tor (2018). Stability assessment of PITT tracer candidate compounds: the case of benzyl alcohols. Journal of Petroleum Science and Engineering. ISSN 0920-4105. 167, p. 517–523. doi: 10.1016/j.petrol.2018.04.027. Full text in Research Archive Show summary

  The selection of compounds used as inter-well tracers has traditionally been done taking into consideration the goal of the test and the ease in analyzing the chemicals used. This often led to improper selection of the tracers and insufficient knowledge about their behavior under typical reservoir conditions, resulting in several unsuccessful inter-well tracer tests. One of the critical characteristics of any conservative tracer is its stability under various reservoir conditions. In this document we present the study methodology and the findings from stability experiments carried out on 5 benzyl alcohols investigated as oil/water partitioning tracers for partitioning inter-well tracer tests (PITT). This is the first of three documents reporting such studies on 3 families of chemicals. A PITT consists of the simultaneous injection of one or more mass-conservative passive and phase-partitioning (one type of active) tracers. PITT is primarily conceived for mature water-flooded oil fields and measures the residual (or even remaining) oil saturation (SOR) in the swept volumes between wells. Knowledge of SOR may be used to identify EOR targets, assess efficiency of EOR operations, and the efficiency of volumetric sweep between wells. This is important information, in particular for the increasing number of mature oil-fields where EOR projects are under consideration and/or development. A thorough knowledge about the static and dynamic properties of the tracers under reservoir conditions is required both to ensure successful field tests, and also to increase accuracy of the data obtained from them. 4-Chlorobenzyl alcohol, 2,6-Dichlorobenzyl alcohol, 4-Methoxybenzyl alcohol, 3,4-Dimethoxybenzyl alcohol, and 4-Hydroxybenzyl alcohol were tested in brine under simulated reservoir conditions with temperatures up to 150 °C during 12 weeks, at different pH values, and in the presence of typical sedimentary basin rock materials, sandstone, carbonate rock (limestone), and clay (kaolinite). 4-Chlorobenzyl alcohol and 2,6-Dichlorobenzyl alcohol were found to be fully stable at all tested conditions. 4-Methoxybenzyl alcohol and 3,4-Dimethoxybenzyl alcohol exhibit thermally induced degradation above 125 °C, but may still be considered for use below this temperature. 4-Hydroxybenzyl alcohol exhibits thermally induced degradation which was found to follow a first order kinetics. The apparent activation energy and pre-exponential constant in the Arrhenius law for the degradation reaction were determined and a kinetic model built. This opens the possibility for use of 4-Hydroxybenzyl alcohol as a non-conservative reservoir tracer to measure temperature or detect thermal fronts.

• Silva, Mario; Stray, Helge & Bjørnstad, Tor (2017). New Potential Tracer Compounds for Inter-well SOR Determination - Stability at Reservoir Conditions. In Ukjent, Ukjent (Eds.), 19th European Symposium on Improved Oil Recovery/IOR Norway 2017. European Association of Geoscientists and Engineers (EAGE). ISSN 9789462822092. doi: 10.3997/2214-4609.201700351. Full text in Research Archive
• Silva, Mario; Stray, Helge & Bjørnstad, Tor (2017). Studies on New Chemical Tracers for Determination of Residual Oil Saturation in the Inter-Well Region. In X, X (Eds.), SPE Oklahoma City Oil and Gas Symposium. 27–31 March 2017, Oklahoma City, Oklahoma, USA. Society of Petroleum Engineers. ISSN 9781613995143. doi: 10.2118/185085-MS. Full text in Research Archive
• Metidji, Mahmoud Ould; Brichart, Thomas; Bjørnstad, Tor & Ferrando-Climent, Laura (2017). New fluorescent tracers for SWCTT. In Ukjent, Ukjent (Eds.), 19th European Symposium on Improved Oil Recovery/IOR Norway 2017. European Association of Geoscientists and Engineers (EAGE). ISSN 9789462822092. Full text in Research Archive
• Haukås, Jarle; Madland, Merete Vadla; Flornes, Kristin Margrethe; Hiorth, Aksel; Valestrand, Randi & Viig, Sissel Opsahl [Show all 14 contributors for this article] (2017). Integration of IOR Research Projects through Generic Case Studies. In Ukjent, Ukjent (Eds.), 19th European Symposium on Improved Oil Recovery/IOR Norway 2017. European Association of Geoscientists and Engineers (EAGE). ISSN 9789462822092. doi: 10.3997/2214-4609.201700260. Full text in Research Archive
• Wangen, Magnus; Sagen, Jan; Bjørnstad, Tor; Johansen, Harald & Souche, Alban Jean-Rene (2016). Models for Calcium Carbonate Precipitation in the Near-Well Zone by Degassing of CO2. Open Petroleum Engineering Journal. 9, p. 178–194. doi: 10.2174/1874834101609160178. Full text in Research Archive Show summary

  Calcium carbonate scale formation is a well known problem for water producing wells. Although there are several types of scale forming processes, we investigate the case of calcium carbonate precipitation when the degassing of CO2 causes the calcium equilibrium concentration to decrease towards a production well. We study a simplified system of carbonate chemistry, which allows for analytical expressions for the porosity loss as a function of time. The precipitation process normally goes from flow-limited away from the well to precipitation-limited close to the well. We derive an expression that estimates the transition zone between these two regimes. Furthermore, we present analytical estimates for the porosity reduction at a given radius as a function of time, including an estimate for each of these precipitation regimes. These analytical results are tested against numerical solutions for the porosity loss, which account for the full set of equations of the model. The analytical models give an accurate estimate of the linear porosity reduction with time, until at least half the porosity is lost. Examples of scale formation are given for the two regimes. Reasonable values for the precipitation kinetics indicate that most production operations have a kinetics-limited regime close to the well. The models also show that this type of scale formation takes place very close to the wells, typically within a few well radii from the walls of the well.

• Stavsetra, Liv; Fure, Kristin; Haugan, Are & Bjørnstad, Tor (2013). Development of an oil tracer labelled with Ba-137m. The European Physical Journal Conferences. ISSN 2101-6275. 50:05002. doi: 10.1051/epjconf/20135005002. Full text in Research Archive
• Stamatakis, Emmanuel; Stubos, A; Bjørnstad, Tor & Muller, Jiri (2013). Calcite scale prediction at the near-well region: A radiotracer approach. In Haugan, Are (Eds.), TRACER 6 - The 6th International Conference on Tracers and Tracing Methods. Oslo, Norway, June 6-8, 2011. EDP Sciences. ISSN 9782759810055. p. 03004-p.1–04004-p.6. doi: 10.1051/epjconf/20135003004. Full text in Research Archive Show summary

  Effective prediction of calcite scaling requires a reliable thermodynamic model for the prediction of the scaling tendency, a kinetic model for the prediction of scaling rate and a transport model to simulate flow in a porous medium. The accurate prediction of the scale deposition can warn the engineers to “treat” the formation around the wellbore in time. In addition, the prediction of the distribution of the scale deposition can direct the engineers to ensure the placement of the inhibitors into the formation zones where the deposition is expected, thus maximizing the probability of successful prevention of formation damage and minimizing at the same time the amount of the required inhibitors. In this contribution, we present a geochemical computational model that combines existing thermodynamic and kinetic models for CaCO3 precipitation, with treatments of flow and diffusion in electrolyte systems, in an one-dimensional porous medium. The geochemical model has the ability to predict the distribution of scale deposition along and around the production wells, as well as the distribution of formation damage (pore blocking, permeability reduction) around the wells.

• Samadani, Fereshteh; Alstad, Jorolf; Bjørnstad, Tor; Stavsetra, Liv & Omtvedt, Jon Petter (2010). Development of a SISAK extraction system for chemical studies of element 108, hassium. Radiochimica Acta. ISSN 0033-8230. 98(12), p. 757–764. doi: 10.1524/ract.2010.1787. Full text in Research Archive
• Eriksen, Dag Øystein; Haugen, Odd Benny & Bjørnstad, Tor (2009). Enhanced oil recovery methods studied by gamma tracer scanning at simulated reservoir conditions. Journal of Radioanalytical and Nuclear Chemistry. ISSN 0236-5731. 280(2), p. 287–292. doi: 10.1007/s10967-009-0513-9. Full text in Research Archive

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• Bjørnstad, Tor; Portela, J. I. Borroto; Brisset, P.; Chankow, N.; Charlton, J.S. & Solis, M.A. Conejo [Show all 18 contributors for this article] (2013). Radiotracer Generators for Industrial Applications. International Atomic Energy Agency. ISBN 9789201354105. 203 p. Full text in Research Archive
• Abidin, Z.; Berne, P.; Bjørnstad, Tor; Jin, J.-H.; Khan, I.H. & Leclerc, J.-P. [Show all 13 contributors for this article] (2012). Application of Radiotracer Techniques for Interwell Studies. International Atomic Energy Agency, IAEA. ISBN 9789201256102. 231 p. Full text in Research Archive

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• Selvam, Arun Kumar Panneer; Metidji, Mahmoud Ould; Krivokapic, Alexander; Silva, Mario & Bjørnstad, Thor (2021). Multi-responsive Nanocarriers – A Contemporary Approach for Single Well Chemical Tracer Tests. Full text in Research Archive Show summary

  The single-well chemical tracer test (SWCTT) is the tool of choice of operators for the assessment of residual oil saturation (SOR) in oilfields. Hundreds of SWCTTs have been reported since the introduction of the test in 1971. The basis for the SWCTT is the use of a reactive phase-partitioning tracer (typically an ester) that will hydrolyse and generate the passive tracer (s) “in-situ”. This presents one of largest drawbacks of the SWCTT, as the hydrolysis step typically requires the sampled well to be shutoff for a few days. Additionally, the analytical methods available to analyse the SWCTT tracers yield fairly high detection limits, thus large amounts of chemicals are required for the test. Even though the SWCTT is, by far, the most used tracer test to measure SOR, its concepts and design have seen little development up to the present day. The exception to this is the recent introduction of a new class of single-well chemical tracers with detectability in the ng/L range, which significantly reduce the amount of chemicals required. Recent developments in the field of stimuli-sensitive polymeric nanocarriers (especially nanogels) have the potential to overcome significantly reduce the amount of time and chemicals required by SWCTTs, as well as dramatically increase the portfolio of available tracers. Nanogels are “intelligent” highly crosslinked polymeric networks which serve as “cargo vehicles” due to their stimuli-sensitive nature. This property, opens the possibility of simultaneously loading a nanogel with passive and partitioning tracers, transport them inside the reservoir, and triggering their release in a fast, efficient and controlled manner. Nanogels can be synthesized to respond to a wide variety of external stimuli such as temperature, pH, electric or magnetic fields etc, based on the polymeric constituents. Multi-responsive nanogels sensitive to temperature and pH were synthesized for the application. A passive and partitioning tracer were loaded to these said carriers and the release studies were conducted with different stimuli. It is noted that the response of the nanocarriers to the external stimuli are instantaneous. We propose to present our findings about the concept, tracer loading and release from the nanocarriers and potential design of a single well tracer test based on multi-responsive nanogels, as well as discussing the main obstacles the technology faces, possible ways of overcoming them, and the improvements it will bring to SWCTTs.

• Selvam, Arun Kumar Panneer; Metidji, Mahmoud Ould; Silva, Mario; Krivokapic, Alexander & Bjørnstad, Thor (2020). Thermo-Sensitive Nanogels for Targeted Tracer Release in Push and Pull Operations. Full text in Research Archive Show summary

  The single-well chemical tracer test (SWCTT) is widely used in the determination of residual oil saturation (SOR) in the near-well region. SWCTTs typically require large amounts of chemicals and some days of well shut-down. In the present paper, we propose using thermo-sensitive nanogel carriers for targeted release of tracers for SWCTTs. This approach has the potential to significantly reduce the time and amount of chemicals required by a SWCTT. The targeted tracer release method was inspired by previously developed drug delivery applications using stimuli-sensitive nano-capsules. Nanoparticles loaded with medical cargo were synthesised to target specific sites. The release of the active principles would then be triggered by an in-situ (temperature, pH) or ex-situ (magnetic field, light) stimuli. A novative approach to address the current limitation of classical SWCTT is based on the biomedical background. It consists in using a poly-N-isopropylacrylamide (pNIPAm) based nanogel, known for its thermo-sensitive nature, to ensure the in-situ delivery of tracer molecules. This effect is explored as a mechanism to both load and release the tracers for a SWCTT. PNIPAm nanogels or hydrogels are highly hydrophilic, cross-linked polymeric networks. When the temperature of the solution is increased above the lower critical solution temperature (LCST) of PNIPAm molecule, the capsules exhibit a reversible collapse effect, causing the release of the tracer molecules. The hydrodynamic diameters of capsules were measured using Dynamic Light Scattering (DLS) and were found to be 195 nm at 25 °C and 73 nm at 45 °C. The nanogels exhibit a reduction in volume to 8 times when the temperature is increased from 25 °C to 45 °C. This change in volume acts as a lock-in mechanism once the tracer is loaded and open-up to release loaded tracers. The study of the encapsulation and release of tracer compounds was achieved using passive and partitioning tracers loaded into the structures. The capsules showed a significant tracer loading efficiency. For studying the release rate and mechanism, increase in temperature was used to trigger the release of tracers. Although the SWCTTs are the most used tracer tests by the oil industry, their development have been relatively slow since it was originally introduced in 1973 (Deans 1971). The present study aims at presenting a novel approach on how nanotechnology can be used to reduce the large amounts of chemicals and time required by classical SWCTTs. Concepts and results about the synthesis of the nano-carriers, loading and releasing of the tracers are presented and discussed.

• Silva, Mario; Metidji, Mahmoud Ould; Stray, Helge & Bjørnstad, Tor (2019). Alkylpyrazines - from the “Dinner Table” to the Oilfield: A New Class of Partitioning Tracers. Full text in Research Archive
• Selvam, Arun; Metidji, Mahmoud Ould; Viig, Sissel Opsahl & Bjørnstad, Tor (2019). Nanoparticle tracers for petroleum reservoir studies. Full text in Research Archive
• Metidji, Mahmoud Ould; Silva, Mario; Krivokapic, Alexander & Bjørnstad, Tor (2019). Synthesis and Characterization of a Reactive Fluorescent Tracer and its Possible Use for Reservoir Temperature's Data Collection. Full text in Research Archive
• Selvam, Arun Kumar Panneer; Metidji, Mahmoud Ould; Silva, Mario; Viig, Sissel Opsahl; Madland, Merete Vadla & Bjørnstad, Tor (2019). Nanoparticle tracers for petroleum reservoir studies. Full text in Research Archive
• Metidji, Mahmoud Ould; Krivokapic, Alexander; Silva, Mario; Bjørnstad, Tor; Selvam, Arun & Cathles, Lawrence (2019). Contribution to the study on nanoparticles as oil-reservoir tracers. Full text in Research Archive
• Bjørnstad, Tor; Metidji, Mahmoud Ould; Krivokapic, Alexander & Viig, Sissel Opsahl (2018). Nanoparticles as oil detectives? Full text in Research Archive
• Bjørnstad, Tor (2018). On-line analyses of mass transport using neutrons. Full text in Research Archive
• Silva, Mario & Bjørnstad, Tor (2018). Non-Conservative Tracers for Temperature Assessment in the Interwell Region of Oil Reservoirs. Full text in Research Archive
• OULD-METIDJI, Mahmoud; Silva, M.H. Lopes Da; Ferrando-Climent, L.; Krivokapic, A. & Bjørnstad, Tor (2018). Future Prospect For Reservoir Tracer Technology: Benefits, Obstacles and Development. Full text in Research Archive Show summary

  Abstract: Objectives/Scope: This study provides an outlook on the major benefits, advantages and drawbacks encountered with tracers currently used for residual oil saturation (SOR) determination employing single-well chemical tracer test (SWCTT) and partitioning inter-well tracer test (PITT) methods, as well as the strategies designed to rise above the obstacles in the process of new tracer development. Methods, Procedures, Process: Both SWCTT test and PITT have seen slow development since their introduction, while the challenges faced by today’s industries have significantly evolved. Most drawbacks encountered in published field cases with these tests arise from our ability to detect and quantify the tracer compounds and/or their inadequate selection/testing. The present work has been focused on the development of new tracers, their testing and qualification, and improvement of the analytical methods to quantify them. Strategies to reduce the cost of tracer tests, like on-site or online analysis of the tracers, have also been considered. Results, Observations, Conclusions: Typically, in a common SWCTT large amounts of hydrolyzing esters are injected into the well. The results suggest the possibility of significantly reducing the amount of chemicals used in these tests. This will contribute to mitigate the safety hazard of the operation and reduce possible modification of the near-well conditions through in-situ generation of high amount of acids liberated during the hydrolysis of the esters. Furthermore, the hydrolysis rate is pH dependent and is a crucial parameter for the test results interpretation, therefore using a smaller amount of chemicals will reduce possible interferences in the results. On the other hand, more and properly tested PITT tracers with sufficiently sensitive analytical methods (ppb-ppt levels) will contribute for the dissemination of these tests. It is important to note that a PITT tracer should endure the harsh reservoir conditions for long periods of time in the range of months to years. It should also comply with growing restrictive environmental regulations, as for example on the Norwegian continental shelf, where strict limits are imposed regarding the amount and nature of the injected compounds. Novel/Additive Information: A thorough understanding of the tracers’ behavior together with a new generation of tracers will contribute to improve both accuracy and feasibility of SOR determination. This will facilitate the use of tracer tests in the oil-field, thus improving reservoir characterization which is a key-factor in the selection of EOR techniques to maximize economical oil recovery.

• Metidji, Mahmoud Ould; Krivokapic, Alexander; Silva, Mario; Cathles, Lawrence & Bjørnstad, Tor (2018). Nanotracers intended for EOR-operations. Full text in Research Archive
• Vinningland, Jan Ludvig; Valestrand, Randi; Hiorth, Aksel; Bjørnstad, Tor; Klöfkorn, Robert & Viig, Sissel Opsahl [Show all 12 contributors for this article] (2018). The National IOR Centre of Norway. Full text in Research Archive
• Bjørnstad, Tor (2017). Nuclear-Based Monitoring of Industrial Mass Flow I: The potential use of Small Transportable Neutron Generators. Full text in Research Archive Show summary

  Radiotracers for industrial monitoring are produced mainly by two main methods: 1) Activation in research nuclear reactors (RNR) or at charged particle accelerators, and 2) by radiotracer generators (RG). Both methods face challenges: 1. The production by activation is often difficult from both administrative and technical reasons. Administrative reasons imply that the production of specific radionuclide has to be known and authorized at the irradiation facilities. Technical reasons imply that irradiation facilities are often non-existing in many countries. Where irradiation facilities do exist, there are limitations due to periodical shut downs. Finally, transportation time between irradiation facilities and industrial site limits again the use of short half-life radiotracers. 2. The number of commercially available radiotracer generators for industrial use is rather limited for the moment. Other options for nuclear-based monitoring of industrial mass flow that appear may therefore be interesting to pursue. One such option is the application of recently developed small-sized neutron generators. Two types of neutron generators are available using deuterium-deuterium (DD) reaction (neutrons at 2:45 MeV) and deuterium-tritium (DT) reaction (neutrons at 14:1 MeV). Commercial DT generators may produce neutron outputs of ¡1011 n/s. Unlike isotopic neutron sources, the neutron generators contain no radioactivity (except the inventory of tritium in the DT neutron generator) making them inherently safe (no external radiation) when turned off. This presentation will review the current status of such neutron generators and discussed possible applications for use in industrial in situ or even on-line monitoring processes. The various approaches include on-site production of radiotracer by off-line irradiation of suitable target, on-line and in situ generation pulses of short-lived radiotracers from macroelements in the flow, direct continuous activation of matrix elements in the flow, activation of injected pulse of a stable chemical compound, PGNAA of injected non-radioactive tracer pulse, neutron transmission measurement after pulse injection of a strong neutron absorber and others. The broad industrial use of such techniques is at present in its infancy, and a considerable R&D work remains to be done to ensure the robustness of the different approaches.

• Bjørnstad, Tor (2017). Can functionalized nanoparticles be used as reservoir tracers? Full text in Research Archive
• Bjørnstad, Tor; Stavsetra, Liv; Krivokapic, Alexander; Eriksen, Dag Øistein & Vascon, Alessio (2017). Hydrometallurgy in mineral mining and urban mining. Full text in Research Archive
• Metidji, Mahmoud Ould; Kelesoglu, Serkan; Silva, Mario & Bjørnstad, Tor (2017). Laboratory assessment of nanotracers for oil reservoir characterization. Full text in Research Archive
• Silva, Mario; Stray, Helge & Bjørnstad, Tor (2017). PITT Tracer Candidates: Stability at Reservoir Conditions. Full text in Research Archive
• Silva, Mario; Stray, Helge & Bjørnstad, Tor (2017). New Chemical Tracers for Determination of Residual Oil Saturation in the Inter-Well Region - Initial Studies. Full text in Research Archive
• Bjørnstad, Tor (2017). Keynote Lecture: Recent development in nuclear methods for process monitoring. Full text in Research Archive Show summary

  In many fields of process monitoring, nuclear methods constitute a technically indispensable tool. However, the use of open or encapsulated radioactive sources is increasingly under public scrutiny, often because of misunderstandings or lack of knowledge. In order to sufficiently mitigate these perceived shortcomings and make the use of nuclear monitoring methods acceptable by process owners and the public, one has to substantiate reduction of any unnecessary human or environmental risks associated with such technologies. For open radioactive sources, i.e. mainly in the form of radiotracers (aqueous, organic or particulate), focus are now on increased application of short-lived radionuclides whenever these can be used. Short-lived radionuclides are commonly produced by neutron irradiations in nuclear reactors or by charged particle reactions at particle accelerators. Hence, due to transportation time and logistics, there is an upper practical limit to the distance of their use from the radionuclide production facilities. Typical industrial examples are off-shore petroleum production in remote areas or onshore process industry in countries which do not host such production facilities. Therefore, there is an increasing focus on developing industrial brands of radiotracer generators, which are based on a secular equilibrium between the long-lived mother and the short-lived daughter radionuclides. This presentation will give some examples of such generators and define the status of their development. Additionally, many long-lived encapsulated radioactive sources used in fixed mountings today (two examples are 60Co and 137Cs) may, in principle, be substituted by the use of small neutron generators which can be turned on and off on demand. The recent years’ development and availability of such transportable neutron generators give, in fact, several new technical possibilities, some of which are summarily mentioned here: 1. on site production of short-lived radionuclides for injection into processes, 2. on-line mounting onto transportation pipelines for in-situ and on-line generation of short-lived tracers directly in the process stream, 3. application of prompt gamma-ray spectra from neutron-induced nuclear reactions generated in the process stream (PGNA) for monitoring of specific mass movement, 4. the use of neutron transmission (thermal and fast neutrons) or reflection (thermal neutrons) monitoring of specific mass movement, 5. generation of prompt gammas in external fixed target for gamma transmission experiments (mass density measurements), and more. This presentation will also describe some of these emerging possibilities in some detail. The use of equipment and methods described here leads to reduced radiation exposure and virtually no left-over activity or radio-contamination after the monitoring process is completed.

• Bjørnstad, Tor (2016). Tracer-based reservoir evaluation and SOR determination. Full text in Research Archive
• Bjørnstad, Tor (2016). The possible role of nanoparticle tracers in measurements of residual oil saturation in the near-well area. Full text in Research Archive
• Bjørnstad, Tor; Silva, Mario; Brichart, Thomas; Krivokapic, Alexander & Viig, Sissel Opsahl (2016). Development of new tracers for SOR measurements in IW and SW application - Some recent results and future plans. Full text in Research Archive
• Silva, Mario & Bjørnstad, Tor (2016). Solid-Phase Microextraction as Sample Preparation Technique in Tracer Technology. Full text in Research Archive
• Bjørnstad, Tor; Stavsetra, Liv; Fure, Kristin; Opel, Karsten; Haugan, Are & Krivokapic, Alexander (2016). Radiotracer-based monitoring of liquid carry-over from gas scrubbers. Full text in Research Archive
• Bjørnstad, Tor (2016). Reactor-produced radionuclides for tracing operations in industry and civil engineering. Full text in Research Archive
• Rollwagen, Joe & Bjørnstad, Tor (2015). Mapping it out: Tracer technology and the search for oil. [Journal]. IAEA Bulletin, September 2015. Full text in Research Archive
• Bjørnstad, Tor (2015). Radiotracers Applications in Oil Fields: Enhancing the Recovery of Oil. Full text in Research Archive
• Bjørnstad, Tor (2015). Mineral exploitation and hydrometallurgical methods. Full text in Research Archive
• Bjørnstad, Tor (2014). Brief about tracer technology and the National Norwegian IOR-Centre. Full text in Research Archive
• Bjørnstad, Tor (2014). A flavour of nano-particles as tracer agents for IOR. Full text in Research Archive
• Bjørnstad, Tor (2014). Aspects of how tracer compounds can contribute to optimize EOR/IOR processes. Full text in Research Archive
• Bjørnstad, Tor; Haugan, Are; Stavsetra, Liv & Fure, Kristin (2014). Radiotracer generators for application in process industries. Full text in Research Archive
• Bjørnstad, Tor (2014). The use of transportable neutron sources for industrial monitoring. Full text in Research Archive
• Madland, Merete Vadla; Hiorth, Aksel & Bjørnstad, Tor (2014). Presenting the 2 R&D Themes for The National IOR Centre of Norway. Full text in Research Archive
• Bjørnstad, Tor (2014). Neutron generators in industry and civil society. Full text in Research Archive
• Bjørnstad, Tor; Haugan, Are; Stavsetra, Liv & Fure, Kristin (2014). Multiphase flow in separators and scrubers: Condition monitoring. Full text in Research Archive
• Bjørnstad, Tor (2014). The Role of Tracers in Optimization of EOR/IOR Operations. Full text in Research Archive Show summary

  After a brief introduction on the general aspects of water- and gas-based oil recovery methods, the presentation is focused on remaining (or residual) oil saturation and potential for recovery by tertiary methods. The concept of Interwell Tracer Technology by simultaneous use of passive and phase-partitioning tracers is then introduced as a means to measure both flooding patterns and remaining (residual) oil saturation in flooded areas between wells. Single-well push-and-pull tracer technology is also covered to measure residual oil saturation in-situ in the near-well zone (5-10 m from the wellbore) by use of reactive tracers, adding some information on recent technology development. The presentation is rounded off by tracer-based methods for depth-differential well fluid in-flow to detect "good and bad" zones in the well, and the potential use of "smart" functionalized tracers to measure properties of the reservoir (salinity, pH, temperature and others) of importance to EOR-operations.

• Bjørnstad, Tor (2013). Beyond Traditional Flow Assurance. Full text in Research Archive
• Bjørnstad, Tor; Eriksen, Dag Øystein & Omtvedt, Jon Petter (2013). Radiochemistry and hydrometallurgy - two synergetic fields. Full text in Research Archive
• Bjørnstad, Tor (2013). The Role of Tracer Technology in Future Reservoir Management. Full text in Research Archive
• Bjørnstad, Tor (2013). Brief about Petroleum Activities at IFE. Full text in Research Archive
• Bjørnstad, Tor (2013). Application of neutron generators in industry. Full text in Research Archive
• Bjørnstad, Tor (2012). Application of gamma-ray detection equipment in the petroleum industry. Full text in Research Archive
• Bjørnstad, Tor (2012). Monitoring Multiphase Flow in Separators and Scrubbers - Combined Radiotracer and Sealed Source Technique. Full text in Research Archive
• Bjørnstad, Tor (2012). Tracer Technology for Interwell Reservoir Examination - Achievements and Future Challenges. Full text in Research Archive
• Bjørnstad, Tor (2012). Radioaktivitet i vår hverdag - delvis til ulempe men også til nytte og forbedret helse. Full text in Research Archive
• Bjørnstad, Tor (2012). Possible development of nuclear technology for industrial monitoring applications. Full text in Research Archive
• Bjørnstad, Tor (2011). Oljedetektivene - de syngende molekyler. Full text in Research Archive
• Bjørnstad, Tor (2011). Flow Assurance Challenges in Geothermal Energy Production - Mineral Scaling. Full text in Research Archive
• Bjørnstad, Tor (2011). Extraction of Th from Norwegian Mineral Resources. Full text in Research Archive
• Fure, K.; Stavsetra, L. & Bjørnstad, Tor (2011). Experimental Studies on Generation of Short-Lived Radiotracers of Daughter Products from the Nuclear Genetic Relationships 68Ge - 68Ga and 137Cs - 137mBa, -a Progress Report. Full text in Research Archive
• Bjørnstad, Tor; Dugstad, Ø.; Hartvig, S.K. & Haugan, A. (2011). SAGD-Related Oil Recovery: Fluid Tracing Challenges. Full text in Research Archive
• Bjørnstad, Tor (2010). In the climate perspective - what is the role of nuclear power? Full text in Research Archive
• Bjørnstad, Tor (2010). Doses, dose effects and safe operations. Full text in Research Archive
• Bjørnstad, Tor (2010). Tracer field operations. Full text in Research Archive
• Bjørnstad, Tor (2010). Development of tracer technology for EOR and production optimization. Full text in Research Archive
• Bjørnstad, Tor (2010). Reservoir management and enhanced oil recovery – the role of tracers. Full text in Research Archive
• Omtvedt, Jon Petter; Alstad, Jorolf; Bjørnstad, Tor; Dullmann, C.E.; Gregorich, K.E. & Gupta, N.S. [Show all 11 contributors for this article] (2010). Superheavy Element Chemistry with SISAK. Full text in Research Archive
• Bjørnstad, Tor (2010). Oil generation, reservoir assessment and petroleum production – a primary. Full text in Research Archive
• Bjørnstad, Tor (2010). Radioactivity and nuclear characteristics – a primary. Full text in Research Archive
• Bjørnstad, Tor (2010). Mechanisms of mineral scaling in geothermal wells studied by nuclear techniques. Full text in Research Archive
• Bjørnstad, Tor (2010). Tracer technology for geothermal reservoir examination. Full text in Research Archive
• Bjørnstad, Tor; Fure, Kristin & Stavsetra, Liv (2009). Development of industrial radiotracer generators at IFE - chemical, toxic and radiotoxic considerations. Full text in Research Archive
• Hassfjell, Sindre; Haugan, Are & Bjørnstad, Tor (2009). 47Ca-aided studies of CaCO3 scaling rates at low saturation ratios. Full text in Research Archive
• Bjørnstad, Tor (2009). Mercury in petroleum – technical and HSE challenges. Full text in Research Archive
• Eriksen, Dag Øystein; Haugan, Are; Bjørnstad, Tor; Halvorsen, S.G; Torgersen, H.J.T. & Haugen, Odd Benny [Show all 7 contributors for this article] (2009). A two-dimensional gamma scanner for performing flooding experiments at oil reservoir conditions. INCS News. VI(4), p. 7–13. Full text in Research Archive
• Bjørnstad, Tor (2009). The use of radioisotope technology on well operation, oil transportation and process studies of petroleum reservoirs. Full text in Research Archive
• Bjørnstad, Tor (2008). Recent advances in tracer technology for production optimization. Full text in Research Archive
• Bjørnstad, Tor (2008). Development of tracer technology for production optimization. Full text in Research Archive
• Bjørnstad, Tor (2008). Exploration and Production R&D at Institute for Energy Technology. Full text in Research Archive
• Bjørnstad, Tor; Brisset, Patrick; Gardner, Robin Pierce; Kuznetsov, Aleksandr & Moreira, Rubens Martin (2016). Neutron Generators for Tracing Applications. International Atomic Energy Agency, IAEA. Full text in Research Archive
• Abdullah, Jaafar; Alami, Rachad; Abdelwahed, Haifa Ben; Bjørnstad, Tor; Calvo, Carlos Sebastian & Dagadu, Christian Priesley Kofi [Show all 17 contributors for this article] (2014). Radiometric methods for measuring and modelling multiphase systems - progress report No.2. International Atomic Energy Agency (IAEA). Full text in Research Archive
• Bjørnstad, Tor; Jin, Joon-Ha; Calvo, Wilson Aparecido; Boutaine, Jean-Louis; Charlton, Stuart & Leclerc, Jean-Pierre [Show all 8 contributors for this article] (2014). Report on the Consultant Meeting on "The Current Status and Future Trends on Radioisotope Applications in Industry". International Atomic Energy Agency. Full text in Research Archive
• Berg, Øivind; Bjørnstad, Tor; Dahlgren, Sven; Nøvik, Sven; Rondeel, Wilhelm & Totland, Arne (2012). Thorium - en framtidsressurs i Oslofjordregionen? Regiongeologen Buskerud, Telemark og Vestfold fylkeskommuner. Full text in Research Archive
• Samadani, Fereshteh; Omtvedt, Jon Petter & Bjørnstad, Tor (2010). Liquid Chemistry of Hassium Tetroxide using Osmium in Model Experiments with SISAK. Universitetet i Oslo. Full text in Research Archive
• Bjørnstad, Tor; Borroto, J.I.P.; Brisset, P.; Chakravarty, R.; Chankow, N. & Charlton, J.S. [Show all 15 contributors for this article] (2009). Evaluation and validation of radioisotope generator-based radiotracers for industrial applications - 2nd progress report. International Atomic Energy Agency (IAEA). Full text in Research Archive

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