Print this pageFrequency Analysis of Geophysical Logs and the Cyclostratigraphic Sequence Framework of the Brent Group, Norwegian Offshore
NIO, S. DJIN, and SHOGO HIRAHARA
Frequency analysis of wireline log data is able to evaluate and detect the presence of different magnitudes of stratigraphic breaks and to measure the wavelength and amplitude of these high-frequency cycles within the logs. In addition, it shows the hierarchical relationship between the wavelengths and amplitudes of these high-frequency cycles. An integrated frequency model of a well results in a curve showing time-related cyclic sedimentation patterns and changes of basin accommodation.
An example is shown in this paper from the Brent Group of the Norwegian offshore. A frequency modelling of well 34/7-14 shows the cyclic pattern of sedimentation related to climate c.q. sea level fluctuations and basin subsidence. The large-scale trend is characteristic for the whole region and can be more or less related to the existing lithostratigraphic subdivision. The smaller scale pattern however, shows a complex cyclic variation reflecting an interplay between local sedimentation and basin dynamic processes.
A frequency modelling of 14 wells enabled the establishment of a high-resolution isochronous correlation framework. Time correlation lines established from the latest biostratigraphic data shows largely an agreement with the correlation. Moreover, a much higher resolution was achieved by using cyclostratigraphic sequence correlation.