Effect of Hydrocarbon Presence and Properties on the Magnetic Signature of the Reservoir Sediments of the Catcher Area Development Region, UK North Sea

Abstract

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.

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

“…Thermodynamic and experimental studies suggest that compared to pyrrhotite, greigite requires a lower supply of labile organic matter, higher supply of reactive iron, lower sulphide concentration and finer grained sediments (Kao et al, 2004). Pyrrhotite and greigite have also been identified in sandy and muddy sediments respectively of the same stratigraphic level (Roberts and Turner, 1993;Abdulkarim et al, 2022b). We can infer from these studies that the precipitation of pyrrhotite at OWTZ is probable as this zone usually falls within sandy intervals in petroleum reservoirs.…”

“…The magnetic signatures of the hydrocarbon reservoirs are complex and variant (Reynolds et al, 1990;Liu et al, 2006;Emmerton et al, 2013;Roberts, 2015;Abubakar et al, 2020;Badejo et al, 2021aBadejo et al, , 2021bAbdulkarim et al, 2022bAbdulkarim et al, , 2022a. The behaviour of oil-stained sandstones when heated will also be variant even within the oil leg, OWTZ and water leg.…”

“…These processes have been shown to involve the formation, alteration and destruction of magnetic minerals (Head et al, 2010;Badejo et al, 2021b). The magnetic minerology of this region may therefore be variant from the overlying and underlying zones and could be identifiable through magnetic techniques (Badejo et al, 2021b;Abdulkarim et al, 2022b).…”

Combining Paleomagnetic and Re‐Os Isotope Data to Date Hydrocarbon Generation and Accumulation Processes

“…The chemical processes leading to magnetic mineral formation in the presence of hydrocarbons is complex, and depends on the complex interplay between the host reservoir rocks, sulfur content of the hydrocarbons, origin of the hydrocarbons, the redox conditions and temperature/depth of remagnetization (Abdulkarim et al., 2022; Badejo et al., 2021; Machel, 1995; Perkins, 2022). Generally, hydrocarbons produce reductive environments leading to the formation of iron sulphides (Machel, 1995; Zhang et al., 2018), however, in very low‐sulfur hydrocarbon environments, magnetite formation has been widely observed and reported (e.g., Perkins, 2022).…”

Interpreting high-temperature magnetic susceptibility data of natural systems

“…In recent years, the Natural Magnetism Group at Imperial College London has used HT-χ analysis extensively in its study of a wide range of rock types, including basalts, ophiolite, and sedimentary rocks ( Emmerton et al, 2013;Berndt and Muxworthy, 2017;Badejo et al, 2021b;Abdulkarim et al, 2022b). We have come up with procedures for identifying different minerals from HT-χ data.…”