Analysis of Shallow Seismic Data for Improved Understanding of Sediment Geobodies

Abstract

The shallow portion of conventional 3D seismic surveys are an under-utilised source of high quality data on sediment geobodies. The high frequency content of these data result in high resolution of the internal and external architecture of key elements, producing data that can be used as input for reservoir models in deeper intervals. This project has systematically extracted geometric data from the shallow section of a series of 3D seismic volumes. All of the data are classified within the SAFARI framework, which was developed to describe outcrop and modern reservoir analogs. Linking data from different sources in a common framework provides a unique insight into subsurface architecture. The main seismic dataset used in this study was the CNS/NNS MegaSurvey from Petroleum Geo-Services ASA (PGS), which covers large parts of the Central and Northern North Sea. Detailed analysis of two areas within this dataset are presented: 1) a Paleogene shoreface made up of eastwards prograding clinoforms in the Outer Moray Firth and 2) Miocene to recent deposits around the Lomre Terrace, offshore Sognefjord. Each area covers roughly 1000 km2. Mapping has revealed the detailed evolution of the depositional systems. Dimensional data include the area, thickness, length and width of the clinoform bodies, clinoform dip angle, channel dimensions and the shoreline trajectories. The prograding clinoforms in the Moray Firth show a clinoform dip variation over their width, highlighting that clinoform dip measurements are position-sensitive. Additionally clinoform dip coupled with thickness allows distinction between transgressive and regressive clinoform bodies. The rate at which the beds taper is also a useful tool in seismic sequence stratigraphy. The East Sand Utsira Unit is genetically independent from the main Utsira Formation. It shows a radial, distributary channel pattern. Width and thickness plots show a homogenous distribution through the unit and testify a potential link between measurements, paleogeography and distance from source. In addition to providing analog data for modeling, comparing the datasets shows significant differences between the Eocene shorefaces and Miocene fluvial dominated delta, which may be related to differences in source area geology and the Miocene cooling of the climate leading to the onset of glaciation.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017