Details DGM-deep V4 onshore

General workflow

The applied modelling workflow is common practice in oil and gas exploration and includes the interpretation of horizons from 3D and 2D seismic data in the time domain (two way travel time). Time grids result from interpolation of seismic horizon picks using a gridding algorithm (convergent gridding). Subsequently, a conversion to the depth domain is made using a velocity model built from well log and checkshot data. The interpreted well markers help to identify the horizons in the seismic data and they provide an anchorpoint for a tie to the correct depth at the well location after time-depth conversion. After time-depth conversion the misties of each surface grid with the well marker depths are analyzed and kriged over the model area. Abnormally high misties caused by recognized local features, such as salt domes and faults, are filtered out and corrected locally. This process does not eliminate all aberrant data and it should be acknowledged that misties can be generated in all steps of the workflow. The resulting well residual (mistie) grids are combined with the time-depth converted grids to obtain a well-tied stratigraphic model, i.e., that acknowledges the well data (see also Kombrink et al., 2012). In a final step the models’ uncertainty is addressed by calculating standard deviation grids resulting from stochastic simulations of those horizons that are based on seismic interpretation.

Modelled units

The DGM-deep v4.0 model comprises the geometrically coherent succession of 11 seismic interpreted horizons and one thickness-based horizon, which were modeled at 250x250m grid resolution. The seismically interpreted horizons represent the (near) bases of the following lithostratigraphic units and include the Limburg Group (DC, Late Carboniferous), Zechstein Group (ZE, late Permian), the Lower and Upper Germanic Trias groups (RB+RN) , the Altena Group (AT, Early and Middle Jurassic), the Schieland and Niedersachsen groups (S, Late Jurassic-Early Cretaceous, ), the Rijnland Group (KN, Early Cretaceous), the Chalk Group (CK, Late Cretaceous- Early Paleogene), the Lower and Middle North Sea groups (N, Paleogene) and the Upper North Sea Group (NU, Neogene). Two horizons have been interpreted at respectively subgroup and formation level; i.e. the Caumer Subgroup (DCC) and the Posidonia Shale Formation (ATPO; Toarcian near base Middle Jurassic). The base of the Lower and Upper Rotliegend Group (RV+RO, Permian) is constructed by adding a thickness grid based on well data to the depth of the base Zechstein Group .

Data updates DGM-deep v4.0

Figure 3 shows the focus areas for the newly released onshore DGM-deep v4.0 model. The model is based on a rigorous (re-)interpretation of onshore 3D seismic surveys. In the Roer Valley Graben (Cenozoic model) and the Province of Limburg, analogue 2D seismic lines have been vectorised and the digital product was re-interpreted. For the DGM-deep v4.0 area 894 wells have been selected for further use in model building. All wells were previously interpreted for earlier releases of DGM-deep (v1.0-v2.0) and a number of additional wells in the Roer Valley Graben have been re-interpreted. The onshore time model was depth converted with the VELMOD-3 velocity model, which is an update of VELMOD-2 (More information Van Dalfsen et. al., 2006 and VELMOD-1 & -2). The map of VELMOD-3 wells shows the location of all onshore wells used to build the velocity grids (location map VELMOD-3). 833 out of 1636 on- and offshore wells have been consulted for the onshore VELMOD-3 velocity model. Time horizons have been clipped at pre-defined layer boundaries and merged into one compiled model in the time domain. These layer boundaries which were defined in previous studies (DGM-deep v1.0 & 2.0) have been edited in the areas of the new 3D seismic interpretations. Fault polygons have been included in the convergent gridding process in areas with 2D seismic interpretations because gridding of a sparsely distributed dataset would otherwise result in poorly defined fault traces. Fault polygons used in the gridding stem from a recently updated fault model in the Roer Valley Graben, and from DGM-deep v2.0 in the remainder of the 2D-area.

Deliverables

Model units are available in 2 formats: ARCGIS and ZMAP. For each stratigraphic interval, several data types can be downloaded. Table 2 lists all data types and stratigraphic units.


Table 2: Data types and stratigraphic units