ALBERT

Description: The integrity of casing and cement is of utmost importance in order to increase the lifecycle and to improve safe operations of geothermal wells. This contribution focuses on the potential of real-time downhole monitoring techniques along fiber optic cables which are permanently installed behind casing. Distributed fiber optic temperature and strain sensing technology are used to measure thermal as well as load signatures during the completion of a low-enthalpy well for geothermal energy storage (Gt BChb1/2015, ATES Fasanenstrasse, Berlin, Germany). Gravel and cement pumping was monitored with distributed strain sensing. The pumping of gravel leads to a density change in the annulus which results in a measureable strain reading on the fiber optic cable. A simultaneous measurement with a gamma-gamma density log shows that the strain data from the fiber indicates the position of the gravel head in the annulus. In addition, a delayed consolidation of the gravel packing was monitored with the fiber. During cement pumping, it was observed that fluid shear stresses generate a measureable strain on the cable. The magnitude of these forces can be used to estimate rheological parameters such as fluid density and viscosity of the pumped medium. An experimental study was conducted to validate the field observations. Using distributed strain sensing, we can extract relevant downhole information (such as fluid/material changes) in real-time without interfering with the operational schedule of a well.

Description: The determination of seismic velocities and their distribution in the subsurface is the target of a large number of geophysical methods. We utilize distributed acoustic sensing (DAS) data, recorded during a 9 days long, continu- ous survey performed on the Reykjanes peninsula, Iceland, to investigate the shallow velocity structure of the area. DAS is an emerging technology to record temporal strain changes experienced by a solid body using fibre-optic cables as an equivalent to a linear, one component broadband seismometer array. Once a fibre-optic cable is in- stalled, DAS systems can provide a dense channel spacing down to 25 cm. Continuous data was recorded with a fibre-optic cable installed behind the 22 1/2” anchor casing of well RN-34 in the Reykjanes geothermal field. Useful signals were obtained up to a depth of approximately 190 m below surface with a trace spacing of one meter. During the DAS measurement drilling commenced for the 9 5/8” production liner in approximately 2500 m depth. To investigate the velocity structure, we use sources provided by activities on the drill site e.g. falling objects. The seismic motion propagates along the fibre-optic cable downhole; we automatically pick amplitude maxima of waves in the records. We also apply seismic ambient noise techniques (seismic interferometry), although generally applied to data recorded at the surface. We apply the standard processing steps of seismic interferometry tem- poral normalization, spectral withening, and stacking. The virtual shot gathers reveal strong asymmetry between the causal and acausal part, which suggests that most of the noise is generated by the drill site itself. We discuss velocity estimations obtained from this study with others obtained by an active surface wave experiment using a fibre-optic cable at the surface.

Description: Reflectance spectroscopy in the visible-infrared and shortwave infrared (450–2500 nm) wavelength region is a rapid, cost-effective and non-destructive method that can be used to monitor heavy metal (PTE, potential toxic elements) contaminated areas. Due to the PTE pollution that has accumulated in the course of wastewater treatment, the existence of Technosols presents an environmental problem, a potential source for PTE uptake by vegetation, or even the release of PTEs into groundwater. In this study, multivariate procedures using Partial Least Squares Regression (PLSR) and Random Forest Regression (RFR) are applied to quantify relationships between soil heavy metal concentration (Cr, Cu, Ni, Zn) and reflectance data of highly contaminated Technosols from a former sewage farm near Berlin, Germany. Laboratory measurements of 110 soil samples in four different preparation steps were acquired with HySpex hyperspectral cameras. The impact of the different preparation steps, namely “oven-dried”, “sieved”, “ground”, “LOI”, was evaluated for its potential to enhance the method performance or to reduce the time-consuming soil sample preparation. Furthermore, different spectral pre-processing methods were evaluated regarding improvements of spectral modelling performance and their ability to minimise noise and multiple scattering effects. Considering the optimal coefficient of determination (R2), PLSR shows an improving performance and accuracy with increasing preparation steps such as ground or LOI for all metals of interest (R2_Cr: 0.52–0.78; R2_Cu: 0.36–0.73; R2_Ni: 0.19–0.42 and R2_Zn: 0.41–0.74). RFR shows a weaker estimation performance for all metals, even when using higher sample preparation levels (R2_Cr: 0.36–0.62; R2_Cu: 0.17–0.72; R2_Ni: 0.20–0.35 and R2_Zn: 0.26–0.67). The results show that an application of methods such as PLSR for the prediction of PTE concentration in Technosols is still a challenge but provides more robust estimations than the user-friendly RFR method. Additionally, this study shows that PTE estimation performance in heterogeneous soil samples can be improved by increased laboratory soil preparation steps and further spectral pre-processing steps.

Description: To date, information about the wellbore integrity of high temperature and high pressure geothermal wells is scarce. Hardly any measurement data is available about the thermal and mechanical load onto the subsurface installation (casing and cemented annulus) during the operation of such wells. In order to monitor the response of the subsurface installation to changing load conditions, a fiber optic cable was installed behind casing of a geothermal well. To increase the knowledge about the wellbore integrity and to benefit from the combined application of different fiber optic sensing technologies, temperature, strain as well as acoustic noise measurements were performed during well completion and testing. These include the distributed temperature sensing (DTS) technology, based on Raman scattering, as well as the distributed strain and distributed acoustic sensing (DAS) technologies, both based on Rayleigh scattering. Here, we present information about the laboratory experiments, the cable installations and downhole measurement campaigns together with results of our analysis. It could be shown that the fiber optic measurements are well suited to monitor the well completion procedures. In addition, the technology offers a possibility to monitor well integrity throughout the lifetime of a geothermal well.

Description: The Northeast German Lowland Observatory (TERENO‐NE) was established to investigate the regional impact of climate and land use change. TERENO‐NE focuses on the Northeast German lowlands, for which a high vulnerability has been determined due to increasing temperatures and decreasing amounts of precipitation projected for the coming decades. To facilitate in‐depth evaluations of the effects of climate and land use changes and to separate the effects of natural and anthropogenic drivers in the region, six sites were chosen for comprehensive monitoring. In addition, at selected sites, geoarchives were used to substantially extend the instrumental records back in time. It is this combination of diverse disciplines working across different time scales that makes the observatory TERENO‐NE a unique observation platform. We provide information about the general characteristics of the observatory and its six monitoring sites and present examples of interdisciplinary research activities at some of these sites. We also illustrate how monitoring improves process understanding, how remote sensing techniques are fine‐tuned by the most comprehensive ground‐truthing site DEMMIN, how soil erosion dynamics have evolved, how greenhouse gas monitoring of rewetted peatlands can reveal unexpected mechanisms, and how proxy data provides a long‐term perspective of current ongoing changes.