Quantitative Clinoform Characterization — Triassic Barents Sea Offshore Northern Norway

Abstract

Shelf-edge clinoforms are well-documented in the literature as demarcating nearshore from deepwater, and because of this they are routinely used to predict depositional environments, paleobathymetry, basin configuration and changes in relative sea-level. The Early to Mid-Triassic Norwegian Barents Sea Basin is characterized by pronounced basinward-stepping clinoforms which has been attributed shelf-edge deltas and lowstand systems, but drilling campaigns targeting potential clinoform topset reservoirs have so far been disappointing. This study investigates the sedimentological characteristics of the clinoform succession in order to look for spatio-temporal variations and explain their variability in light of relative sea-level variations and topset deposition in the associated large scale deltaic system landward of the clinoforms. The Triassic clinoform succession has been interpreted both in 2D and 3D seismic over a 400×300 km area, with sequence boundaries being based on palynological zonations and regional maximum flooding surfaces. The clinforms s are decompacted according to lithological information from core and well log data, enabling a comparison to modern and ancient counterparts. In addition, decompacted geometries are compared throughout the basin to reveal differences in depositional character. Sigmoidal clinoforms dominate in the Early Triassic succession, whereas the Mid-Triassic succession is characterized by more oblique clinoform geometries that have a more homogeneous lithological succession with lower acoustic impedance contrast and are consequently less accentuated than the underlying. Both of which are distinguishable from prodeltaic clinoforms. Discrete growth faults are also observed on the clinoform slope. This change can be attributed sedimentological variations in the delta topset. Particularly the Mid-Triassic is characterized by thicker topset accumulation and larger channelized deposits, indicating increased sediment influx, contrasting the more tidally dominated sigmoidal clinoform topset of the Early Triassic. This study shows how different clinoform geometries have developed in response to differential sediment supply both spatially and temporally over a 400×300 km area and through tens of millions of years. In this shale-dominated succession, the best reservoir rocks are not necessarily found in the clinoform topset. This understanding has implications for how clinoform successions are assessed in an exploration context.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016