Publications
339 results found
Turney J, Muxworthy AR, Sims M, et al., 2024, Quantifying the characteristics of magnetic oil-water contacts in mature hydrocarbon reservoirs and their capacity for understanding hydrocarbon remigration, Geophysical Journal International, Vol: 237, Pages: 570-587, ISSN: 0956-540X
Increasing magnetization within mature hydrocarbon reservoirs provides a new technique in identifying oil–water contacts (OWCs) in cored wells with the potential to assess yield thereby reducing the need for further exploration. Authigenic precipitation of magnetic minerals at OWCs may also help locate palaeocontacts (PCs), where structural changes to the petroleum system have caused hydrocarbon remigration. This study determines the magnetic characteristics of magnetic enhancements at OWCs and possibly PCs in silliclastic and carbonate reservoirs at the Wytch Farm oil field, Wessex Basin, UK. Increases in saturation magnetization and susceptibility are observed at the OWC in 11 of the 12 analysed cored reservoirs owing to the increased presence of magnetite and vivianite. Geochemical analysis and shallow reservoirs suggest biogenic and inorganic mineral precipitation is extensive at the OWC depending on iron, sulphur and phosphorus availability. Similar magnetic characteristics have been observed in magnetic enhancements above the OWC in numerous wells which may represent OWCs before a basin-wide easterly tilt caused hydrocarbon remigration in the Cenozoic. Multiple magnetic enhancements above the OWC in westerly onshore wells, suggest this remigration may have occurred as numerous phases.
Døssing A, Kolster ME, Silva ELS, et al., 2024, Pre-existing structural control on the recent Holuhraun eruptions along the Bárðarbunga spreading center, Iceland, Scientific Reports, ISSN: 2045-2322
North T, Muxworthy A, Williams W, et al., 2024, The effect of stress on paleomagnetic signals: a micromagnetic study of magnetite's single-vortex response, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276
In this study we use micromagnetic modeling to show that the magnetizations of magnetically single-vortex particles rotate toward the stress axis on the application of a differential compression stress. This is the exact opposite response to magnetically single-domain particles, which previously provided the theoretical underpinning of the effect of stress on the magnetic signals of rocks. We show that the magnetization directions of single-vortex and equant single-domain particles are altered by much lower stresses than previously predicted, c.f., 100 versus 1,000 MPa; where a change in magnetization is defined as a rotation of >3° after the removal of stress. The magnetization intensity of assemblages also drops by ∼20%–30% on the application and removal of stress of ∼100 MPa. Given that single-vortex particles are now thought to dominate the magnetization of most rocks, future studies should account for paleomagnetic directional uncertainties and potential underestimation of the ancient magnetic field intensity.
Nagy L, Tauxe L, Williams W, et al., 2023, Chasing tails: Insights from micromagnetic modeling for thermomagnetic recording in non-uniform magnetic structures, Geophysical Research Letters, Vol: 49, ISSN: 0094-8276
Paleointensities are key to understanding the formation and evolution of Earth and are determined from rocks which record magnetic fields upon cooling; however, experimental protocols for estimating paleointensities frequently fail. The primary reason is that laboratory protocols assume that rocks are dominated by uniformly magnetized, single-domain grains, instead of much more common non-uniformly magnetized grains. Our model for larger grains shows a multiplicity of stable domain states; with preferred states changing as a function of temperature. We show that domain state distribution depends on the thermal history of the sample—in nature and the laboratory. From numerical thermomagnetic modeling, we show that particles with non-uniform domain states will theoretically fail standard experimental paleointensity protocols, preventing us from determining reliable ancient geomagnetic field intensities. We propose that recognizing this type of behavior, and the resulting bias, will yield more reliable paleointensity records, and a better understanding of the Earth.
Turney J, Weiss D, Muxworthy AR, et al., 2023, Greigite formation in aqueous solutions: critical constraints into the role of iron and sulphur ratios, pH and Eh, and temperature using reaction pathway modelling, Chemical Geology, Vol: 635, Pages: 1-16, ISSN: 0009-2541
Greigite forms as an intermediate phase along the pyrite reaction pathway. Despite being considered metastable, it is observed in numerous shallow natural systems, suggesting it could be a unique proxy for diagenetic and environmental conditions. We use thermodynamic reaction pathway modelling in PHREEQC software, to understand the role of iron and sulphur ratios, pH and Eh, and temperature on the formation and retention of greigite in aqueous solutions. With newly available experimental thermodynamic properties, this work identifies the chemical boundary conditions for greigite formation in aqueous solutions. Greigite precipitation is likely favourable in anoxic and alkaline aqueous solutions at or below 25 °C. Our numerical experiments show that greigite is closer to saturation in iron-rich solutions with minor sulphur input. Greigite precipitation in strongly alkaline solutions suggest polysulfides and ferric iron-bearing minerals may be favourable reactants for its formation. Greigite precipitates at iron and sulphur concentrations that are over two orders of magnitude greater than iron sulphide-hosted natural porewaters. This disparity between model and field observations suggest microenvironments within bulk solutions may be important for greigite formation and retention. These constraints suggest greigite is more likely to form alongside pyrite in shallow, non-steady state aqueous solutions.
Noble JPP, Bending SJ, Muxworthy AR, et al., 2023, Simplified Model for Minor and Major Loop Magnetic Hysteresis and its Application for Inference of Temperature in Induction Heated Particle Beds, Journal of Physics D: Applied Physics, ISSN: 0022-3727
Di Chiara A, Muxworthy AR, Trindade RIF, et al., 2023, Mesoproterozoic geomagnetic field strength from Nova Guarita mafic dykes (Amazon Craton), Studia Geophysica et Geodaetica: a journal of geophysics, geodesy, meteorology and climatology, ISSN: 0039-3169
Muxworthy AR, Turney J, Qi L, et al., 2023, Interpreting high-temperature magnetic susceptibility data of natural systems, Frontiers in Earth Science, Vol: 11, ISSN: 2296-6463
High-temperature susceptibility (HT-χ) data are routinely measured in Earth, planetary, and environmental sciences to rapidly identify the magnetic mineralogy of natural systems. The interpretation of such data can be complicated. Whilst some minerals are relatively unaltered by heating and are easy to identify through their Curie or Néel temperature, other common magnetic phases, e.g., iron sulphides, are very unstable to heating. This makes HT-χ interpretation challenging, especially in multi-mineralogical samples. Here, we report a review of the HT-χ data measured primarily at Imperial College London of common magnetic minerals found in natural samples. We show examples of “near pure” natural samples, in addition to examples of interpretation of multi-phase HT-χ data. We hope that this paper will act be the first reference paper for HT-χ data interpretation.
Steele SC, Fu R, Volk MWR, et al., 2023, Paleomagnetic evidence for a long-lived, potentially reversing martian dynamo at ~3.9 Ga, Science Advances, Vol: 9, Pages: 1-13, ISSN: 2375-2548
The 4.1-billion-year-old meteorite Allan Hills 84001 (ALH 84001) may preserve a magnetic record of the extinct martian dynamo. However, previous paleomagnetic studies have reported heterogeneous, nonunidirectional magnetization in the meteorite at submillimeter scales, calling into question whether it records a dynamo field. We use the quantum diamond microscope to analyze igneous Fe-sulfides in ALH 84001 that may carry remanence as old as 4.1 billion years (Ga). We find that individual, 100-μm-scale ferromagnetic mineral assemblages are strongly magnetized in two nearly antipodal directions. This suggests that the meteorite recorded strong fields following impact heating at 4.1 to 3.95 Ga, after which at least one further impact heterogeneously remagnetized the meteorite in a nearly antipodal local field. These observations are most simply explained by a reversing martian dynamo that was active until 3.9 Ga, thereby implying a late cessation for the martian dynamo and potentially documenting reversing behavior in a nonterrestrial planetary dynamo.
Perkins JR, Fraser AJ, Muxworthy AR, et al., 2023, Basin and petroleum systems modelling to characterise multi-source hydrocarbon generation: A case study on the inner Moray Firth, UK North Sea, Marine and Petroleum Geology, Vol: 151, Pages: 106180-106180, ISSN: 0264-8172
Baker EB, Muxworthy A, 2023, Using Preisach theory to evaluate chemical remanent magnetization and its behavior during Thellier-Thellier-Coe paleointensity experiments, Journal of Geophysical Research: Solid Earth, ISSN: 2169-9356
Hu J, Zhang Y, Jia D, et al., 2023, Combining paleomagnetic and Re-Os isotope data to date hydrocarbon generation and accumulation processes, Journal of Geophysical Research: Solid Earth, ISSN: 2169-9356
North TL, Collins G, Davison T, et al., 2023, The heterogeneous response of Martian meteorite Allan Hills 84001 to planar shock, Icarus, Vol: 390, ISSN: 0019-1035
Impact-generated shock waves can change the physical properties of meteorites and their constituent minerals. Accounting for these effects is key to recovering information about the early solar system from meteorite observations. ALH 84001 is a rare ancient sample from the Martian crust, providing a unique window into the thermal and metamorphic evolution of Mars. A well-studied meteorite, past geochemical and petrologic investigations have attempted to deduce its thermal and impact history with some contradictory results. By simulating the passage of a planar shock wave through a synthetic analog for samples of ALH 84001 using the iSALE-2D shock physics code we have determined the meteorite’s likely thermodynamic and physical response during an impact. Our simulations show that heterogeneous shear heating, induced by the planar shock wave, can produce strong thermal gradients on the sub-millimeter ‘mesoscale’ throughout the meteorite, even in relatively weak shock waves (5 GPa). We are able to place new constraints on deformation events experienced by the meteorite during its time on the parent body, including the maximum pressure ALH 84001 has experienced since it acquired its remanent magnetization and its subsequent ejection from Mars.
Elmore RD, Muxworthy A, Heij G, et al., 2023, Remagnetization and Diagenesis, Frontiers in Earth Science, ISSN: 2296-6463
Moreno R, Williams W, Muxworthy A, et al., 2022, The meaning of maxima and minima in first order reversal curves: determining the interaction between species in a sample, Journal of Magnetism and Magnetic Materials, Vol: 564, ISSN: 0304-8853
First-order reversal curves (FORCs) are a characterization technique for magnetic materials used in a wide range of research fields. Since their first application in the Earth Sciences two decades ago, their importance in science has been continuously growing and new experimental techniques have been subsequently designed based on the original idea of FORCs. Nonetheless, very recent experimental works on very well designed and simple magnetic structures demonstrate that even for the most simple cases the interpretation of FORC data lacks understanding. In this work, we address this problem analytically, explaining the meaning of maxima, minima and noisy tails and set a strategy to extract the interaction field between magnetic structures. The origin of this interaction field is often the magnetostatic energy, however, we propose that this strategy could be applied for estimating exchange interactions too.
Muxworthy A, Lam C, Green D, et al., 2022, Magnetic characterisation of London’s airborne nanoparticulate matter, Atmospheric Environment, Vol: 287, Pages: 1-8, ISSN: 1352-2310
Iron-bearing particulate matter produced by vehicle emissions is known to be toxic. To better quantify potential health risks, we have conducted the first magnetic study of a time-series of London's inhalable particulate matter (<10 μm, PM10), captured by three monitoring stations in central London (Marylebone Road, Earl's Court Road and Oxford Street) through 2010 and 2012. We conducted room-temperature analysis on all the samples, and a limited number of samples were analysed at both high and low temperatures. The high-temperature measurements identified magnetite as the dominant magnetic phase. The low-temperature measurements revealed high numbers of nanoparticles, which, assuming magnetite, are in the grain-size range 1–4 nm. It is estimated that as much as ∼40% of the total magnetic signal at 10 K is from particles <4 nm, that are magnetically ‘invisible’ at room-temperature and are being routinely under-estimated in room temperature-based magnetic studies. From the low-temperature measurements, the total concentration of magnetite was estimated at ∼7.5%, significantly higher than previously reported. The room-temperature magnetic data were compared with other pollution data, e.g., NOX and PM10, and meteorological data. Mass-dependent terms like the saturation magnetisation were found to display a strong correlation with NOX and PM10, indicating a common source for these pollutants, i.e., vehicle emissions. Magnetic coercivity measurements, which are independent of abundance, and provide information on grain-size, were consistent across all three sampling localities, again suggesting a major dominant source. Relatively small variations in coercivity were correlated with meteorological events, e.g., temperature and precipitation, suggesting preferential removal of larger airborne grains, i.e., >50 nm.
Abdulkarim M, Muxworthy AR, Fraser A, 2022, High temperature susceptibility measurements: A potential tool for the identification of oil water transition zone (OWTZ) in petroleum reservoirs, Frontiers in Earth Science, Vol: 10, ISSN: 2296-6463
Determining the position and thickness of the oil water transition zone (OWTZ) in hydrocarbon reservoirs is important to reserveestimation and production planning. This paper describes a magnetic method of identifying this zone. High temperaturesusceptibility (HT‐χ) measurements on core samples from Paleogene reservoirs of the UK Central North Sea revealed distinctsignatures around the oil water interface. Rapid increases in susceptibilities at temperatures < 250 °C were observed forsamples around the oil water interface unlike the main oil leg where alteration involving increase in susceptibility occurred atsignificantly slower rates and higher temperatures. The HT‐χ data together with Mössbauer measurements revealed that thevariation in alteration characteristics is due to the increasing concentration of hexagonal pyrrhotite and/or lepidocrocite aroundthe oil water interface. Hexagonal pyrrhotite was identified in reservoirs existing at temperatures of < 80 °C, whilelepidocrocite dominated the signature around the contact of deeper reservoirs. These observations suggest that the precipitationof hexagonal pyrrhotite is related to OWTZ centred biogenic activities i.e., biodegradation. The dominance of lepidocrocite indeeper diagenetic settings has been related to hydrolysis of hydrocarbon at the oil water interface, together with cessation ofbiogenic activities.
North TL, Muxworthy AR, Collins GS, et al., 2022, THERMOREMANENT MAGNETISATION RECORDED DURING IMPACT-INDUCED COMPACTION EXPERIMENTS ON SYNTHETIC CHONDRITIC METEORITES, LSPC, Publisher: WILEY, ISSN: 1086-9379
Abdulkarim MA, Muxworthy A, Fraser A, et al., 2022, Effect of hydrocarbon presence and properties on the magnetic signature of the reservoir sediments of the Catcher Area Development (CAD) region, UK North Sea, Frontiers in Earth Science, Vol: 10, Pages: 1-20, ISSN: 2296-6463
This paper presents a detailed study investigating the effect of hydrocarbon presence on magnetic mineral diagenesis in sediments from the Catcher Area Development (CAD) region, UK North Sea, between 1,000 and 1,500 m (True Vertical Depth Sub-Sea). Magnetic analysis of core samples from hydrocarbon fields of the region and nearby dry-well sandstones (background) was carried out to determine if their signatures can serve as a proxy for understanding petroleum reservoir systems. From the background samples, nanometric and micron-sized magnetite, hematite and titano-iron oxides, were identified. Hydrocarbon presence in the reservoir sediments was found to diminish the iron-oxide signature and favour the precipitation of hexagonal pyrrhotite, siderite and potentially vivianite, lepidocrocite, greigite and paramagnetic iron sulphides. Hexagonal pyrrhotite was found at the oil-water transition zones. This relationship is possibly related to biodegradation at this interface. Siderite was found in increased abundance at shallower depths within the reservoir, which we attribute to hydrocarbon vertical migration and biodegradation. The interbedded shales also experienced significant magnetic mineral diagenesis that depended on its proximity to the hydrocarbon plume. These findings suggest that mineral magnetism can be applied to the identification of oil-water transition zones, reserve estimation, production planning and the determination of hydrocarbon migration pathways. It also suggests that mineral magnetic methods can be used to estimate the timing of hydrocarbon migration.
Roberts AP, Heslop D, Zhao X, et al., 2022, Unlocking information about fine magnetic particle assemblages from first-order reversal curve diagrams: Recent advances, EARTH-SCIENCE REVIEWS, Vol: 227, ISSN: 0012-8252
Abdulkarim M, Muxworthy A, Fraser A, et al., 2022, Siderite occurrence in petroleum systems and its potential as a hydrocarbon-migration proxy: a case study of the Catcher Area Development and the Bittern area, UK North Sea, Journal of Petroleum Science and Engineering, ISSN: 0920-4105
Roberts AP, Zhao X, Hu P, et al., 2021, Magnetic domain state and anisotropy in hematite (alpha-Fe2O3) from first-order reversal curve diagrams, Journal of Geophysical Research. Solid Earth, ISSN: 2169-9356
Muxworthy A, Baker E, 2021, ThellierCoolPy: A cooling-rate correction tool for paleointensity data, G3: Geochemistry, Geophysics, Geosystems: an electronic journal of the earth sciences, Vol: 22, Pages: 1-8, ISSN: 1525-2027
We report a new approach of implementing cooling-rate corrections in absolute ancient magnetic field intensity (paleointensity) studies. Nearly all methods of determining paleointensity estimates rely on rocks having recorded a thermoremanent magnetization (TRM), on cooling from above the rock’s constituent minerals’ Curie temperature. Typically paleointensity estimates are made by comparing natural TRM, with a TRM induced in the laboratory; however, TRM intensity has long been reported to be dependent on cooling rate. Natural cooling rates are impractical in laboratories. We have developed a new cooling-rate correction method and corresponding software (ThellierCoolPy), that directly corrects the unprocessed paleointensity data, using first-order reversal curve data collected on a sister sample. This site tailored cooling-rate correction has a unique correction for each temperature step within the paleointensity data set. This new method differs from previous approaches which apply a blanket cooling-rate correction independent of the material properties of the sample. Paleointensity data from historical lavas from Parícutin, Mexico, are used to demonstrate the new software. For this data set, it is shown that cooling time of 1 million years yields a reduction of the paleointensity of ∼7%. The software is available for download.
Noble JPP, Bending SJ, Sartbaeva A, et al., 2021, A Novel In Situ High-Temperature Magnetometry Method for Radiofrequency Heating Applications, ADVANCED ENERGY MATERIALS, Vol: 12, ISSN: 1614-6832
Badejo SA, Muxworthy A, Fraser A, et al., 2021, Identification of magnetic enhancement at hydrocarbon/water contacts, American Association of Petroleum Geologists (AAPG) Bulletin, Vol: 105, Pages: 1973-1991, ISSN: 0149-1423
Identifying the depths of the hydrocarbon-fluid contacts in a reservoir is important for determining hydrocarbon reserves and production planning. Using core samples from the Tay sandstone reservoir in the Central North Sea, we show that thereis a magnetic enhancement at the hydrocarbon-fluid contacts, that is detectable both through magnetic susceptibility measurements and magnetic hysteresis measurements. We observed this magnetic enhancement at both gas-oil and oil-water contacts, that have been independently identified using non-magnetic methods; we did not consider gas-water contacts in this study. We demonstrate that this magnetic enhancement is due to the precipitation of new nanometric iron oxide (magnetite) and iron sulphide (greigite)phases. The magnetic enhancement may be caused by diagenetic changes or preferential biodegradation at the top of the oil column during early filling and at the oil water contact. Our findings have the potential to be used to identify paleo-hydrocarbon-fluid contact in both structurally modified fields and failed wells. The technique can also be used to infer the fill history of a basin and calibrate petroleum systems models. Magnetic susceptibility measurements have the advantage that they can easily and quickly be measured in the field on whole core-material.
Badejo SA, Muxworthy AR, Fraser A, et al., 2021, Using magnetic techniques to calibrate hydrocarbon migration in petroleum systems modelling: A Case Study from the Lower Tertiary, UK Central North Sea, Geophysical Journal International, Vol: 227, Pages: 617-631, ISSN: 0956-540X
Magnetic minerals form or alter in the presence of hydrocarbons, making them a potential magnetic proxy for identifying hydrocarbon migration pathways. In this paper, we test this idea by magnetically measuring core samples from the Tay Fan in the Western Central Graben in the Central North Sea. In a companion paper, 3-D petroleum systems modelling has been carried out to forward model migration pathways within the Tay Fan. Rock magnetic experiments identified a range of magnetite, maghemite, iron sulphides, siderite, goethite and titanohematite, some of which are part of the background signal, and some due to the presence of hydrocarbons. Typical concentrations of the magnetic minerals were ∼10–200 ppm. Importantly, we have identified an increasing presence of authigenic iron sulphides (likely pyrite and greigite) along the identified lateral hydrocarbon migration pathway (east to west). This is likely caused by biodegradation resulting in the precipitation of iron sulphides, however, though less likely, it could alternatively be caused by mature oil generation, which subsequently travelled with the migrating oil to the traps in the west. These observations suggest mineral magnetic techniques could be a rapid alternative method for identifying the severity of biodegradation or oil maturity in core sample, which can then be used to calibrate petroleum systems models.
Badejo S, Fraser A, Neumaier M, et al., 2021, 3D Petroleum Systems Modelling as an exploration tool in mature basins: A study from the Central North Sea, UK., Marine and Petroleum Geology, ISSN: 0264-8172
Hu P, Oda H, Zhao X, et al., 2021, Assessment of magnetic techniques for understanding complex mixtures of magnetite and hematite: the Inuyama red chert, Journal of Geophysics Research - Solid Earth
Abdulkarim M, Muxworthy A, Fraser A, et al., 2021, PRECIPITATION OF SIDERITE IN HYDROCARBON ENVIRONMENT, Pages: 2417-2421
Migration of hydrocarbons in the subsurface has been shown to create an environment that promotes the precipitation and/or alteration of magnetic minerals. For example, iron oxides and iron sulphides have been shown to precipitate due to the reducing conditions created by hydrocarbon migration. Siderite, a paramagnetic mineral with Neel temperature of 37K has been variously identified in hydrocarbon environment and has also been suggested to be an authigenic product of hydrocarbon migration. However, it is commonly found in sedimentary settings. Here we show via experimental studies that siderite is precipitated due to hydrocarbon migrations and suggested the mechanism responsible for this process. Magnetic minerals precipitation along migration pathways suggests the creation of a magnetic fingerprint that if thoroughly understood can be applied to oil and gas exploration.
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