Wavelet transform‐based seismic facies classification and modelling: application to a geothermal target horizon in the NE German Basin

Abstract

At the geothermal test site near Groß Schönebeck (NE German Basin), a new 3D seismic reflection survey was conducted to study geothermal target layers at around 4 km depth and 150°C. We present a workflow for seismic facies classification and modelling which is applied to a prospective sandstone horizon within the Rotliegend formation. Signal attributes are calculated along the horizon using the continuous Morlet wavelet transform. We use a short mother wavelet to allow for the temporal resolution of the relatively short reflection signals to be analysed. Time‐frequency domain data patterns form the input of a neural network clustering using self‐organizing maps. Neural model patterns are adopted during iterative learning to simulate the information inherent in the input data. After training we determine a gradient function across the self‐organizing maps and apply an image processing technique called watershed segmentation. The result is a pattern clustering based on similarities in wavelet transform characteristics. Three different types of wavelet transform patterns were found for the sandstone horizon. We apply seismic waveform modelling to improve the understanding of the classification results. The modelling tests indicate that thickness variations have a much stronger influence on the wavelet transform response of the sandstone horizon compared with reasonable variations of seismic attenuation. In our interpretation, the assumed thickness variations could be a result of variable paleo‐topography during deposition of predominantly fluvial sediments. A distinct seismic facies distribution is interpreted as a system of thicker paleo‐channels deposited within a deepened landscape. The results provide constraints for the ongoing development of the geothermal test site.

Wireline distributed acoustic sensing allows 4.2 km deep vertical seismic profiling of the Rotliegend 150 °C geothermal reservoir in the North German Basin

“…It is furthermore marked by a crossover of the bulk density and neutron porosity curves. Bauer et al (2019) presented an approach to map the distribution and properties of this sandstone layer based on analysis of seismic attributes of the 3-D surface seismic volume.…”

“…So far, two deep research boreholes, the former E GrSk 3/90 hydrocarbon exploration well and the Gt GrSk 4/05 geothermal well (referred to as GrSk3 and GrSk4 in the following), exist at the site. For further development of the site, the implementation of a new stimulation concept and drilling of a new well have been proposed (Blöcher et al, 2015).…”

3-D seismic exploration across the deep geothermal research platform Groß Schönebeck north of Berlin/Germany

“…This allowed the calculation of time-depth conversions and interval velocities along the two boreholes, which have then been extrapolated along the structures into the entire 3-D volume. Detailed well tie studies and examinations are available in dedicated manuscripts with respect to seismic modeling (Bauer et al 2019) and thorough geological interpretation (Norden et al in revision).…”

Cable reverberations during wireline distributed acoustic sensing measurements: their nature and methods for elimination

“…The 3D seismic survey, covering an area of 8 km by 8 km, has its focus on reservoir depths at 4 km. The main goal of the 3D seismic survey was to enhance the comprehension of the geological structures and to reveal the spatial configuration of fault structures (Krawczyk et al ., 2019; Bauer et al ., 2020).…”