Using magnetic techniques to calibrate hydrocarbon migration in petroleum systems modelling: A Case Study from the Lower Tertiary, UK Central North Sea

Abstract

Summary 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, 3D 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.

High temperature susceptibility measurements: A potential tool for the identification of oil-water transition zone in petroleum reservoirs

“…The unaltered samples present with Curie temperature of ~580 °C suggesting the presence of original magnetite. Similar signatures have been observed in oil leg core samples from the Gannet and Guillemot fields, UK Central North Sea (Badejo et al, 2021c).…”

“…The geochemical requirements for the formation of lepidocrocite include a near neutral pH, a non-sulphidic environment and the presence of available iron (Gendler et al, 2005;Roberts, 2015). In a sulphidic environment, iron sulphide(s) will preferentially precipitate (Burton et al, 1993;Roberts, 2015;Badejo et al, 2021c). This likely accounts for the dominance of lepidocrocite at the OWTZ of the Bittern sands and its diminishing signature in the Pict and Bonneville sands.…”

Magnetic Properties of Ferrofluid Change Over Time: Implications for Magnetic Pore Fabric Studies

“…Abubakar et al (2020) found a correlation between strongly magnetic samples and oil-stained samples, while unstained samples were more weakly magnetic. Mineral magnetic techniques have been used to identify hydrocarbon migration pathways and hydrocarbon contamination in soils and sediments (Badejo et al, 2021;Rijal, Porsch, Appel, & Kappler, 2012). Similarly, Gadirov, Eppelbaum, Kuderavets, Menshov, and Gadirov (2018) successfully identified hydrocarbon deposits from magnetic anomalies.…”

Influence of Early Low‐Temperature and Later High‐Temperature Diagenesis on Magnetic Mineral Assemblages in Marine Sediments From the Nankai Trough

“…Temperatures as low as 50°C are sufficient to form new magnetic minerals (Kars et al, 2012). Hydrocarbon generation deeper in the sediment (e.g., Abubakar et al, 2015;Badejo et al, 2021;Elmore et al, 1987;McCabe et al, 1987) and tectonic fluid circulation (e.g., Elmore et al, 2001;McCabe et al, 1989) can lead to abiotic magnetic mineral formation and/or to alteration of pre-existing magnetic minerals. Rock-Eval pyrolysis measurements were carried out to further investigate potential effects of progressive increases in temperature, magnetic mineral content, and catagenesis (high temperature organic matter decomposition).…”