FOCUS

FOCUS on Upper Jurassic sandstones

Publieke samenvatting / Public summary

Upper Jurassic Sandstones: Detailed sedimentary facies analyses, correlation and stratigraphic architectures of hydrocarbon bearing shoreface complexes in the Dutch offshore area

Summary:

This project involved investigating Upper Jurassic and Lower Cretaceous intervals in the eastern part of the Dutch offshore area to provide new insights into the regional and local stratigraphic, depositional and syn-depostional settings. The project strongly improved understanding of the Upper Jurassic and Lower Cretaceous in the Dutch offshore by providing a tectono-stratigraphic framework based on modern concepts of sequence stratigraphy and syn-depositional tectonic models.

Background:

Despite having numerous known reservoirs, the Upper Jurassic and Lower Cretaceous stratigraphic interval still held key questions regarding depositional environments and the preservation of sandy strata. The local and regional correlation of these strata required new analysis and insights. The study area encompassed three main structural provinces, the Dutch Central Graben (DCG), the Terschelling Basin (TB) and the Step Graben (SG), and five platforms, the Cleaver Bank High (CBH), the Central Offshore Platform (COP), the Friesland Platform (FP), the Ameland Block (AB) and the Schill Grund High (SGH). 

Project objective:

This project sought to update and increase knowledge on the distribution and stratigraphic architecture of the Upper Jurassic to Lower Cretaceous reservoir sands in the areas mentioned. It further aimed to decrease uncertainties related to the occurrence, spatial distribution and facies of these sandstones, and build new and robust depositional, stratigraphic and tectono-stratigraphic models based on new biostratigraphic, facies, sequence stratigraphic and structural information. Other goals included relating reservoir/field scale results to key stratigraphic and tectono-stratigraphic events, interpreting core material to better understand the depositional environments encountered, obtaining new time lines to better constrain the local and regional correlation between wells, and to correlate key stratigraphic intervals throughout the study area using standard well correlation techniques combined with seismic interpretation along the same sections.

Project results:

The results obtained from the combination and integration of various analytical techniques were used to produce a new stratigraphic and tectono-stratigraphic model for Upper Jurassic and Lower Cretaceous rock in the northern and eastern part of the Dutch offshore area. The project strongly improved understanding of the Upper Jurassic and Lower Cretaceous in the Dutch offshore by providing a tectono-stratigraphic framework based on modern concepts of sequence stratigraphy and syn-depositional tectonic models. The use of regional seismic and well-correlation panels helped to better constrain the three main depositional sequences identified in the study area as well as their varying preservation potential between the Dutch Central Graben, the Terschelling Basin, the Step Graben and their surrounding platforms. The project did not include any substantive seismic mapping such as time structure, isopach or attribute mapping, leaving those for a follow up project.