Hintze, M. ; Stadler, J. ; Rühaak, W. ; Bär, K. ; Sass, I. (2017)
Transferability of petrophysical and geophysical data between neighboring boreholes: A case study from the North German Basin.
EGW Karlsruhe 2017. Karlsruhe (12.10.2017-13.10.2017)
Konferenzveröffentlichung, Bibliographie

Kurzbeschreibung (Abstract)

Within the scope of the research project “Horstberg III” (Thermalwasserzirkulation in der Tiefbohrung Horstberg Z1 – Charakterisierung eines künstlich geschaffenen Wärmetauschers und geochemische Untersuchungen), carried out at the Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), petrophysical properties of core samples and gamma-ray logs of neighboring boreholes are analyzed and compared to each other in order to test their transferability. The abandoned gas well Horstberg Z1 was used to test the single-well-concept for direct heat production. A water-frac was produced in the Detfurth formation of the Middle Buntsandstein at 3800 m depth. The frac penetrates the Hardegsen formation and ends in the Solling formation. As the original concept proofed only partially successful, an alternative concept was implemented. The two sandstone layers (Detfurth-Sandstone and Solling-Sandstone) are separated by a packer inside the well. Hot water is produced from the shallower Solling-Sandstone and reinjected into the deeper Detfurth-Sandstone. As the sandstone layers are connected through the frac a continuous circulation comparable to a borehole doublet could be created. Hydraulic properties of the fracture were obtained by circulation and tracer tests. Accompanying numerical models serve to evaluate the tracer tests and to estimate the geothermal power and the reservoir capacity. For the parametrization of the models hydraulic and petrophysical rock properties need to be determined. Due to the lack of core samples from the borehole Horstberg Z1, the relevant properties are measured on core samples from a neighboring borehole (Unterlüß T1). In order to test the transferability of the generated data to Horstberg Z1, gamma-ray logs and petrophysical properties of core samples from five boreholes surrounding Horstberg Z1 are compared to each other. Altogether data of six boreholes were analyzed, for four of the wellbores gamma-ray logs are available (including Horstberg Z1) and four contain core samples and results from laboratory measurements (excluding Horstberg Z1). Thermal and petrophysical properties (thermal conductivity and diffusivity, compressional wave velocity, density, porosity, permeability) and the gamma-ray log of the Detfurth-Formation of the Unterlüß T1 borehole show good correlation with the lithological categorization of the core material. The results are analyzed statistically with the aim to obtain statistical parameters for each property and each lithological class (sandstone, claystone, alternating sandstone-claystone sequences). The correlation of the gamma-ray logs from Horstberg Z1, Unterlüß T1 and two neighboring boreholes is quantified with the Pearson correlation coefficient, yielding results between 0.79 and 0.93. It is therefore assumed that the transferability from Unterlüß T1 to Horstberg Z1 is appropriate and that the measurement results can serve to parametrize the numerical models.

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