Microfractures in chalks of Albuskjell Field, Norwegian sector, North Sea: Possible origin and distribution

Journal Article · Tue Feb 01 04:00:00 EST 1983 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6887380

Watts, N L

Production data from many North Sea chalk fields have indicated moderate to considerable contribution to production from natural fractures. This paper illustrates a detailed study of natural fracturing in the Albuskjell field, where gas/condensate hydrocarbons are contained in Upper Cretaceous (Maastrichtian) and lower Tertiary (Danian) chalks. The field is a large halokinetically induced dome located on the northern limits of the productive chalk region known as the Greater Ekofisk area. Examination of core material from wells 1/6-3, 2/4-F10, and 1/6A-10 (Albuskjell), has revealed the presence of two types of fractures. The first appear to be early, are commonly compacted, predominantly healed, and resemble conjugate shear fractures. The second type is related mainly to the tips of stylolites; these are vertical, preferentially open, and are interpreted as tension fractures. Tension fractures form, when the minimum effective stress is reduced to the tensile strength of the chalk, as a result of increased pore-fluid pressure and/or decreased total confining stress due to relative extension. Construction of effective stress versus progressive burial-depth profiles, using three models of overpressure generation, suggests that high pore-fluid pressures alone could not have formed the tension fractures in Albuskjell. Measurements and calculations from depth-converted seismic sections have shown that halokinesis occurred throughout chalk deposition and continued, in a series of pulses, until early Miocene time. Incremental stress values, associated

• Research Organization: Koninklijke/Shell Exploratie en Produktie Laboratorium, Rijswijk
• OSTI ID: 6887380
• Journal Information: Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 67:2; ISSN AAPGB
• Country of Publication: United States
• Language: English

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