Seismic Attribute Analysis In Geothermal Exploration For Carbonate Reservoirs: An Integrated Workflow And Case Study From The Molasse Basin (Jurassic, Germany)

Abstract

Upper Jurassic carbonates are the prime target for deep geothermal exploration in the Molasse basin, South Germany and consist of two main facies types: (1) bedded marly limestone and (2) massive limestone/dolostone. The massive limestone/ dolostone is predominantly formed by sponge/microbial biohermal buildups and are considered as the best geothermal reservoir facies. However, internal heterogeneities of the bioherms as well as the sequence stratigraphic architecture have significant impact on reservoir type and properties. Depending on the stratigraphic position of the biohermal buildups, highest flow rates (>100L/sec) are often associated with: (1) karstification, (2) dolomitization and/or (3) faults and fractures. Data used in this study include borehole cuttings and borehole image logs from 2 geothermal wells as well as a 3D seismic cube of a successful and active geothermal field in the western part of Munich/Germany. The authors present a novel and innovative workflow of 3D seismic attribute analysis that visualizes the lateral and vertical distribution of massive limestone/dolostone versus bedded marly limestone and manages to quantify the presence of reservoir facies versus non-reservoir facies. The studied interval is based on the resolution of the 3D seismic data, subdivided into 7 pseudo-stratigraphic layers. Each of the 7 layers is analyzed using the “sum of magnitude” attribute to distinguish reservoir buildup from non-reservoir basin facies. Seismic interpretation is calibrated with data from 2 geothermal wells including borehole image facies, well logs and borehole cuttings. The seismic maps visualize the distribution and the geometry of reservoir vs. non reservoir facies in a lateral and vertical sense. This novel approach of seismic attribute analysis using pseudo-stratigraphic layers, finetuned to seismic resolution is extremely useful for: (1) quantification of reservoir facies through time and space, (2) geothermal exploration of similar fields and reservoirs and (3) the construction of more predictive static and dynamic reservoir models.

AAPG Datapages/Search and Discovery Article #90346 ©2019 AAPG European Region, 3rd Hydrocarbon Geothermal Cross Over Technology Workshop, Geneva, Switzerland, April 9-10, 2019