Palaeomagnetic characteristics of drill cores from Middle Jurassic delta plain sediments, the Brent Group, North Sea

Hauger, Eirik; Løvlie, Reidar

doi:10.1016/0031-9201(92)90030-y

Cited by 6 publications

(3 citation statements)

References 20 publications

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“…The RCA results also suggest a facies independent magnetomineralogy and grain size dependent coercivity with the highest RCF and RACF values in the sandstones and lowest values in the claystones (Table 1). This agrees with previous observations from the Brent Group (Hauger et al 1992(Hauger et al , 1994Hauger & LOvlie 1992). It implies that the NRM in the Brent Group in the Tampen area is most probably carried by predominantly diagenetically formed magnetic minerals, and thus represents a dominant chemical remanent magnetization (CRM).…”

Section: Remanent Coercivity Analysissupporting

confidence: 86%

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Application of magnetostratigraphy to Brent Group reservoir zonation in the Visund Field

Hauger¹,

Veen

1995

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Magnetostratigraphy has been applied to an increasing number of oil fields in the North Sea region with promising results for detailed chronostratigraphic reservoir correlation. However, the magnetization processes in hydrocarbon reservoir successions, and the potential use of magnetostratigraphy for reservoir zonation purposes, are not very well known. Therefore, aspects of these subjects are discussed on the basis of a magnetostratigraphic study of three different wells covering the Middle Jurassic Brent Group at the Visund Field, northern North Sea. Results from scanning electron microscopy and remanent coercivity analysis suggest that the primary magnetization defining the magnetozones in the Brent Group is a combination of detrital remanent magnetization and a chemical remanent magnetization, probably acquired contemporaneously shortly after deposition. Detailed thermal demagnetization has uncovered an important secondary magnetization component in most of the core samples. This magnetization is probably due to cooling of the cores from a reservoir temperature of about ll0~ to surface temperature, and it causes the main disturbances in the palaeomagnetic results. Based on analyses of individual core samples, characteristic remanent magnetization components have been defined. The magnetopolarity stratigraphy for the individual wells is based on these components and the results are comparable from well to well. The well correlation covers a rock sequence with a thickness of about 200m, and both magnetostratigraphic and biostratigraphic results have been used in combination with the lithostratigraphy. The acme of Corollina represents the most important palyno-event, and the top and bottom of this palynozone is used as the main tie-level for two of the wells. Sixteen additional correlation lines have been derived from the magnetostratigraphic results, six of these considered as tentative. The correlation reveals that the magnetostratigraphic results are facies independent and some of the lithostratigraphic formation lines appear to be diachronous within this deltaic mega-sequence. Although the magnetostratigraphy only provides a relative time framework for the Brent Group, the results are encouraging and suggest the possibility of achieving high resolution chronostratigraphic well correlations for Middle Jurassic reservoir sequences in the northern North Sea area.The application of magnetostratigraphy in the oil industry is rapidly increasing and the method has been used in several oil fields world-wide (e.g. Rey et al. 1993; Hauger et al. 1994; Belkaaloul et al. this vol.; Bryant et al. this vol.).The potential uses of magnetostratigraphy are many and in hydrocarbon reservoir research may reflect: (1) on a regional scale, magnetopolarity stratigraphy can be used for dating and duration assessments of sequences and individual formations (Haq et al. 1988;Harland et al.

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Section: Remanent Coercivity Analysissupporting

confidence: 86%

“…These intervals are totally dominated by minerals such as quartz or carbonate. Plotted on a semi-logarithmic scale, the mode value of the magnetic susceptibility is 320 x 10 -6 SI units, which is a typical value for the Brent Group (Hauger et al 1992(Hauger et al , 1994.…”

Section: Petromagnetic Propertiesmentioning

confidence: 99%

Application of magnetostratigraphy to Brent Group reservoir zonation in the Visund Field

Hauger¹,

Veen

1995

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“…Pyrrhotite is the dominant remanence carrier and occurs within the pyrite grains, mostly as diffuse zones. Such inclusions within pyrite grains appear to be common in marine sediments (Hauger & Løvlie 1992; Elmore & McCabe 1991). The history of the iron sulphides is not established from these studies, but it is suspected that they were in the form of marcasite prior to the hydrocarbons entering the sandstones.…”

Section: Probable Magnetomineralogical Compositionmentioning

confidence: 99%

The origin of bore-core remanences: mechanical-shock-imposed irreversible magnetizations

Shi

Tarling

1999

Geophysical Journal International

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Repeated laboratory‐induced weak mechanical shocking (c. 0.57 kg m s−1 ) of marine sandstone samples showing drilling‐induced remanence, from commercial bore cores from the North Sea and Prudhoe Bay, causes increases in their low‐field susceptibility (χ) and their ability to acquire an isothermal remanent magnetization (IRM). These enhancements are reduced by some 20 per cent by AF demagnetization in 100 mT. Doubling the intensity of the shock doubles the susceptibilities and IRMs acquired. The susceptibility increase ceases after 300 to 400 shocks for the North Sea samples and 20 to 30 shocks for those from Prudhoe Bay, while the IRM saturates after 800–1000 and 30–50 shocks respectively. Continental, haematite‐bearing sandstones from commercial bore cores with no drilling‐induced remanence subjected to the same shocks do not show these effects. Differences in the magnetic mineralogy of shocked and unshocked marine samples suggest that the magnetic enhancement is predominantly due to the creation of pyrrhotite by shock‐induced irreversible crystallographic changes in iron‐bearing sulphides. When shocked during commercial drilling, these new ferromagnetic minerals acquire strong chemical (crystalline) remanences, associated with a wide spectrum of grain sizes, in the magnetic field of the drill string, and these are resistant to both thermal and AF demagnetization. Similar processes are likely in any situation involving the shock of physically metastable iron‐bearing minerals, particularly anoxic sediments. A 5 cm non‐magnetic collar between the drill stem and crown should drastically reduce the magnetic intensity of this effect under commercial conditions, but would not prevent its occurrence.

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Middle Jurassic magnetopolarity stratigraphy of a well-core from the Brent Group, North Sea

Hauger

Løvlie

Svindland³

1992

Physics of the Earth and Planetary Interiors

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Palaeomagnetic characteristics of drill cores from Middle Jurassic delta plain sediments, the Brent Group, North Sea

Cited by 6 publications

References 20 publications

Application of magnetostratigraphy to Brent Group reservoir zonation in the Visund Field

Application of magnetostratigraphy to Brent Group reservoir zonation in the Visund Field

The origin of bore-core remanences: mechanical-shock-imposed irreversible magnetizations

Middle Jurassic magnetopolarity stratigraphy of a well-core from the Brent Group, North Sea

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