Overcoming challenges in the classification of deep geothermal potential

The geothermal community lacks a universal definition of deep geothermal systems. A minimum depth of 400 m is often assumed, with a further sub-classification into middle-deep geothermal systems for reservoirs found between 400 and 1000 m. Yet, the simplistic use of a depth cut-off is insufficient to uniquely determine the type of resource and its associated potential. Different definitions and criteria have been proposed in the past to frame deep geothermal systems. However, although they have valid assumptions, these frameworks lack systematic integration of correlated factors. To further complicate matters, new definitions such as hot dry rock (HDR), enhanced or engineered geothermal systems (EGSs) or deep heat mining have been introduced over the years. A clear and transparent approach is needed to estimate the potential of deep geothermal systems and be capable of distinguishing between resources of a different nature. In order to overcome the ambiguity associated with some past definitions such as EGS, this paper proposes the return to a more rigorous petrothermal versus hydrothermal classification. This would be superimposed with numerical criteria for the following: depth and temperature; predominance of conduction, convection or advection; formation type; rock properties; heat source type; requirement for formation stimulation and corresponding efficiency; requirement to provide the carrier fluid; well productivity (or injectivity); production (or circulation) flow rate; and heat recharge mode. Using the results from data mining of past and present deep geothermal projects worldwide, a classification of the same, according to the aforementioned criteria is proposed

Impact of interfractional target motion in locally advanced cervical cancer patients treated with spot scanning proton therapy using an internal target volume strategy

Background and purpose: The more localized dose deposition of proton therapy (PT) compared to photon therapy might allow a reduction in treatment-related side effects but induces additional challenges to address. The aim of this study was to evaluate the impact of interfractional motion on the target and organs at risk (OARs) in cervical cancer patients treated with spot scanning PT using an internal target volume (ITV) strategy. Methods and materials: For ten locally advanced cervical cancer patients, empty and full bladder planning computed tomography (pCT) as well as 25 daily cone beam CTs (CBCTs) were available. The Clinical Target Volume (CTV), the High Risk CTV (CTVHR) (gross tumor volume and whole cervix), the non-involved uterus as well as the OARs (bowel, bladder and rectum) were contoured on the daily CBCTs and transferred to the pCT through rigid bony match. Using synthetic CTs derived from pCTs, four-beam spot scanning PT plans were generated to target the patient-specific ITV with 45 Gy(RBE) in 25 fractions. This structure was defined based on pre-treatment MRI and CT to anticipate potential target motion throughout the treatment. D98% of the targets and V40Gy(RBE) of the OARs were extracted from the daily anatomies, accumulated and analyzed. In addition, the impact of bladder volume deviations from planning values on target and bowel dose was investigated. Results: The ITV strategy ensured a total accumulated dose >42.75 Gy(RBE) to the CTVHR for all ten patients. Two patients with large bladder-related uterus motion had accumulated dose to the non-involved uterus of 35.7 Gy(RBE) and 41.1 Gy(RBE). Variations in bowel V40Gy(RBE) were found to be correlated (Pearson r = −0.55; p-value <0.0001) with changes in bladder volume during treatment. Conclusion: The ITV concept ensured adequate dose to the CTVHR, but was insufficient for the non-involved uterus of patients subject to large target interfractional motion. CBCT monitoring and occasional replanning is recommended along the same lines as with photon radiotherapy in cervical cancer

Umweltbedeutsame Effekte einer moeglichen Einfuehrung von 'Tempo 30' im Innerortsbereich. T. 3 Einsatzchancen von kleinen umweltschonenden Fahrzeugen im Zusammenhang mit 'Tempo 30' und Verkehrsberuhigung. Typenkatalog und Expertenbefragung

TIB: RN 8422(1990,25) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Permeability estimation from induced polarization: an evaluation of geophysical length scales using an effective hydraulic radius concept

Geophysical length scales defined from induced-polarization measurements can be used in models of permeability (k) prediction. We explore the relative merit of different induced-polarization parameters as proxies of an effective hydraulic radius (reff) that can be used to predict permeability from a modified Hagen–Poiseuille equation. Whereas geometrical measures of the hydraulic radius are good proxies of reff, the induced-polarization measures are not well correlated with reff. However, a new proxy of reff that considers both imaginary conductivity and formation factor shows an improved correlation with reff. The resulting model enables a better quality of permeability prediction compared with the other geophysical length scales, but does not reach the predictive quality of the models based on geometrical length scales. The specific polarizability defined when incorporating the effect of the formation factor on imaginary conductivity appears to be independent of pore geometry, indicating that it is the correct parameter representing the role of the surface electrochemistry on the induced-polarization effect. However, the joint dependence of induced-polarization measurements on both the pore radius and the tortuosity and porosity of the interconnected pore network is a limitation to the widely explored use of induced-polarization measurements to isolate surface properties from volumetric properties of the interconnected pore network

Effect of changing water salinity on complex conductivity spectra of sandstones

We analyzed the influence of pore fluid composition on the complex electrical conductivity of three sandstones with differing porosity and permeability. The fluid electrical conductivity (sigma(w)) of sodium and calcium chloride solutions was gradually increased from 25 mS/m to 2300 mS/m. The expected linear relation between sigma(w) and the real component of electrical conductivity (sigma') of the saturated samples was observed. The imaginary component (sigma '') exhibits a steeper increase at lower salinities that flattens at higher salinities. For a glauconitic sandstone and a high porosity Bunter sandstone, sigma '' approaches an asymptotic value at high salinities. Sodium cations result in larger values of sigma '' than calcium cations in solutions of equal concentration. Debye decomposition was used to determine normalized chargeability (m(n)) and average relaxation time (tau) from spectral data. The behavior of sigma '' is comparable to m(n) as both parameters measure the polarizability. At lower salinity, the relation between m(n) and sigma(w) approximates a power law with an exponent of similar to 0.5. The average relaxation time shows only a weak dependence on sigma(w). The normalized chargeability of sandstone samples can be described by the product of the pore space related internal surface and a quantity characterizing the polarizability of the mineral-fluid interface that depends on fluid chemistry. We introduce a new parameter, the specific polarizability, describing this dependence. We propose relations between polarizability and fluid chemistry that could be used to estimate pore space internal surface across samples of varying sigma(w). We observe a consistent maximum polarizability for quartz dominated siliceous material