Using magnetic techniques to calibrate lateral hydrocarbon migration in basin modelling: A Case Study from the Lower Tertiary, UK Central North Sea
File(s)
Author(s)
Badejo, Sijibomioluwa Adesope
Type
Thesis
Abstract
Pyrolysis experiments and calculated thermostability diagrams show that iron bearing minerals can be produced inorganically during oil formation in the ‘oil-kitchen’ or be precipitated in the reservoir via alteration or replacement of existing minerals. This study applies a novel use of this observation to identify a magnetic proxy for hydrocarbon migration pathways. This is addressed by examining the Tertiary Tay Fan in the Western Central Graben in the Central North Sea. In order to constrain potential migration pathways in the Tay, petroleum systems modelling was carried out in the Western Central Graben, an area well constrained by existing borehole and 3D seismic data. The results demonstrate initial downwards migration from a mature Jurassic (Kimmeridge Clay) source in the Central Graben to the east into an underlying Fulmar Formation carrier followed by vertical migration into the overlying Tertiary sandstones of the Tay and Forties Sandstone Member via structural focus zones. Importantly, the Jurassic source rock is shown to be immature in the west and central study area, requiring long distance lateral migration of at least 30 km as the charge mechanism for the existing Tertiary fields in the west.
Importantly, mineral magnetic analysis identified an increasing presence of ferrimagnetic iron sulphides in core samples along the identified lateral hydrocarbon migration pathway (east to west). This is likely caused by increasingly lower reservoir temperatures and resulting biodegradation leading to the precipitation of iron sulphides. Alternatively, it could be caused by iron sulphides precipitated during early mature oil generation traveling with the oil to the traps in the west. These observations suggest magnetic techniques could be an efficient alternative method for identifying the severity of biodegradation or maturity of oil in core samples which can then be used to calibrate petroleum systems models. Results also hint at the potential for high resolution aeromagnetic surveys to identify shallow subsurface migration pathways. Rock magnetic techniques also identified an enhancement of magnetisation at the hydrocarbon-fluid contacts. The magnetic enhancement is due to the precipitation of new nanometric iron oxide (magnetite) and iron sulphide (greigite) phases. This observation has the potential to be used to identify paleo-hydrocarbon-fluid contact in dry wells or map tilted contacts, which could then be used to infer fill history of a basin or calibrate petroleum systems models.
Importantly, mineral magnetic analysis identified an increasing presence of ferrimagnetic iron sulphides in core samples along the identified lateral hydrocarbon migration pathway (east to west). This is likely caused by increasingly lower reservoir temperatures and resulting biodegradation leading to the precipitation of iron sulphides. Alternatively, it could be caused by iron sulphides precipitated during early mature oil generation traveling with the oil to the traps in the west. These observations suggest magnetic techniques could be an efficient alternative method for identifying the severity of biodegradation or maturity of oil in core samples which can then be used to calibrate petroleum systems models. Results also hint at the potential for high resolution aeromagnetic surveys to identify shallow subsurface migration pathways. Rock magnetic techniques also identified an enhancement of magnetisation at the hydrocarbon-fluid contacts. The magnetic enhancement is due to the precipitation of new nanometric iron oxide (magnetite) and iron sulphide (greigite) phases. This observation has the potential to be used to identify paleo-hydrocarbon-fluid contact in dry wells or map tilted contacts, which could then be used to infer fill history of a basin or calibrate petroleum systems models.
Version
Open Access
Date Issued
2019-03
Date Awarded
2019-07
Copyright Statement
Creative Commons Attribution Non-Commercial No Derivatives licence
Advisor
Muxworthy, Adrian
Fraser, Alastair
Sponsor
Petroleum Technology Development Fund (Nigeria)
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)