Sequence Stratigraphy and Stratigraphic Simulation of the Brent Group, Norwegian North Sea: ABSTRACT

Abstract

Sequence stratigraphic analysis of a well log data base from the Norwegian North Sea has established that the Brent Group is a deltaic complex consisting of four third-order depositional sequences. Sequence 1 was deposited first during northwestern progradation of the delta from the Horda Platform, while sequences 2 and 3 were primarily aggradational. Sequence 4 is characterized by backslapping geometries and a basin wide drowning event which resulted from variably increasing subsidence rates across the basin. The stratigraphic events interpreted in this study are based on the identification of unconformities (sequence boundaries), transgressive surfaces, and maximum flooding surfaces. Dates for these events were established using biostratigraphy from 12 wells. Unlike earlier interpretations, the Oseberg Formation is considered to be part of Sequence 1 and is an incised-valley fill which is genetically related to the distal Rannoch and Etive formations. Also in this study, a new sea level curve is proposed for the Aalenian - Bathonian which has similar frequencies to the Exxon sea level chart, but much smaller amplitudes. This interpretation was simulated in order to estimate the sea level, subsidence, and sediment supply parameters involved in deposition of these sequences. Simulation results indicate that the main deposition of themore » Brent Group occurred during uniform subsidence, while drowning of the depositional system resulted from a sharp, but variable increase in subsidence rates across the basin. Quantitative comparisons between the lithologic percentages in each sequence at well locations and at representative points in the simulation confirm that the simulation presents a unique and reasonable answer.« less