EP9 - Geophysical Monitoring


Aims

The workgroup EP9 wants to image the geological structures in the centre of the Thuringian Basin as well as to identify the physical properties of the in-situ rocks. For this goal a reflection seismic experiment with three profiles and a total length of 76 km was planned, prepared and supervised by EP9. This experiment should not only image the underground of the centre of the Thuringian Basin, which is so far less investigated, it was also used as a preliminary survey for the location of the drilling site of the INFLUINS deep borehole. Thus, the drilling site of the borehole is located at the crossing point of two reflection seismic profiles (Fig. 1). The comprehensive processing and analysing of the reflection seismic data was undertaken by the EP9. The second scientific focus of the workgroup are the borehole geophysical measurements in the INFLUINS deep borehole, which were done along the total depth of 1179 m. Different methods were applied, among others Gamma-Log, Sonic-Log, Neutron-Neutron-Log. Additional to the geophysical measurements also core-logging and rock petrophysical measurements on core-samples were done in the lab to complete this substantial dataset. Since the investigation took place in different spatial scales, it is possible to determine local variabilities as well as essential petrophysical characterisations in the entire area from the centre of the Thuringian Basin to the Top Basement.

Working area

The working area of the EP9 is mainly located at the centre of the Thuringian Basin were the reflex seismic experiment and the deep scientific borehole took place. Furthermore petrophysical investigations were undertaken in several older exploration boreholes in Thuringia.

EP9 Webseite Karte

Fig.1: Location of the three reflection seismic profiles (blue lines) and the drilling site of the INFLUINS deep borehole (red triangle).


Methods

In EP9 geophysical field experiments and petrophysical lab experiments were combined. This combination allows conclusions up to the sub-seismic scale. Beside the data acquisition the substantial processing of the different data sets is in the focus of the work. This is a necessary workflow before geoscientific interpretations can be made. During the INFLUINS drilling three borehole geophysical surveys were conducted after each drilling stage, including measurements of gamma ray, spectral gamma ray, gamm-gamma density, neutron-neutron prosity, resistivity, borehole deviation, susceptibility, temperature, sonic, acoustic televiewer and dipmeter. In the petrophysics laboratory new measurement concepts are developed by EP9. These non-destruktive methods allow investigation with ultrasonic sound at the drilling core samples and other rock samples. Also measurements of thermal conductivity on the surface of "bohrkernhalbflächen" are possible.

Vibratorfahrzeug

Figure 2: Reflection seismic Survey with seismic vibrators around Erfurt.

EP9 Webseite BG1EP9 Webseite BG2

Figure 3: Borehole geophysical measurements after drilling at the INFLUINS deep borehole.

MSCL-Logger

Figure 4: Petrophysical measurements on core-samples of the INFLUINS deep borehole with a multi-sensor-core-logger (MSCL).


Results

A fundamental result of the reflection seismic measurements is the identification of intact geological layers in the surrounding of the borehole location as well as information about the composition, structure and the amount of displacement along the Eichenberg-Gotha-Saalfeld fault-zone and Erfurter fault. Important results of the borehole and core-sample measurements are the complete logging of the petrophysical properties and fluid flows along the entire depth of the scientific deep borehole. The seismic velocities measured by the Sonic-Log can be verified with the inverted velocities of the traveltime tomography (EP1). In addition, with the help of borehole geophysical data a correlation between layer boundaries and the stratigraphic sample description of the cores (EP3) came off. There are close collaborations with EP1, especially in the field of the seismic tomography, and with NWG1 in the frame of common field experiments as well as the identification of petrophysical properties with EP2 and ZPK by the structural interpretation of the geology of the Thuringian Basin. Concluding, EP9 is very good cross-linked inside the scientific frame-work INFLUINS and achieves important essential results, which build the foundation for continuative works in other EPs.

Team

The team of EP9 can be found here.