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Title: Oil and water : fibrous illite diagenesis and the onset of hydrocarbon charge in the petroleum systems of the northern North Sea
Author: Cavanagh, Andrew James
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2002
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Illite growth during oil field burial detrimentally effects reservoir sandstones by reducing permeability. Illite diagenesis can be dated using the isotopic K-Ar decay system. The potential value of this data is the paleocalibration of basin models to illite age related geological events. The fundamental control upon illite growth is a likely combination of solute supply and illite thermodynamic stability. The most important source of solutes for illite growth is the dissolution of potassium feldspar. However, petrographic data from reservoir sandstones from both the U.S. Gulf Coast and the UK North Sea indicate that feldspar dissolution is a continuous process, taking place over a considerable depth interval. Feldspar dissolution reactions are currently taking place in many sandstones where thermodynamics indicate that illite is stable, and where illite might be expected to be grown at the present day. There is no zero Ma age illite found in such sandstones. The implication of episodic illite K-Ar ages is that illite growth is an event-triggered process. Existing published illite data for the Northern North Sea are reviewed, and interpreted as showing episodic growth in the late Mesozoic and Cenozoic consistent with the expected timing of hydrocarbon charge to Northern North Sea oil fields. Experimental isotopic analysis of illite sampled from the Penguin field suggests a complex multiphase filling history for the Penguin field. Two dimensional basin modelling of a small petroleum system based on the geology of the Magnus and Penguin fields, related provinces and local embayments, examines this interpretation of the data. This simple model, the Magus model, supports the hypothesis that the onset of hydrocarbon charge controls the growth of illite within oil field sandstones. A calibrated Magnus model is adapted to examine likely migration timings for the Viking Graben and More Basin. In light of this, a simple explanation is proffered for the general population of illite ages published for the Northern North Sea - fibrous illite diagenesis in the sandstone reservoirs the Northern North Sea oil field is a response to the onset of oil migration.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available