Catchment controls on solute export

Understanding hydrothermal processes during production is critical to optimal geothermal reservoir management and sustainable utilization. This study addresses the hydrothermal (HT) processes in a geothermal research doublet consisting of the injection well E GrSk3/90 and production well Gt GrSk4/05 at the deep geothermal reservoir of Gros Schonebeck (north of Berlin, Germany) during geothermal power production. The reservoir is located between −4050 to −4250 m depth in the Lower Permian of the Northeast German Basin. Operational activities such as hydraulic stimulation, production (T = 150°C; Q = −75 m3 h−1; C = 265 g l−1) and injection (T = 70°C; Q = 75 m3 h−1; C = 265 g l−1) change the HT conditions of the geothermal reservoir. The most significant changes affect temperature, mass concentration and pore pressure. These changes influence fluid density and viscosity as well as rock properties such as porosity, permeability, thermal conductivity and heat capacity. In addition, the geometry and hydraulic properties of hydraulically induced fractures vary during the lifetime of the reservoir. A three-dimensional reservoir model was developed based on a structural geological model to simulate and understand the complex interaction of such processes. This model includes a full HT coupling of various petrophysical parameters. Specifically, temperature-dependent thermal conductivity and heat capacity as well as the pressure-, temperature- and mass concentration-dependent fluid density and viscosity are considered. These parameters were determined by laboratory and field experiments. The effective pressure dependence of matrix permeability is less than 2.3% at our reservoir conditions and therefore can be neglected. The results of a three-dimensional thermohaline finite-element simulation of the life cycle performance of this geothermal well doublet indicate the beginning of thermal breakthrough after 3.6 years of utilization. This result is crucial for optimizing reservoir management.

Geofluids (2010) 10, 406–421

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3D numerical modeling of hydrothermal processes during the lifetime of a deep geothermal reservoir

Numerical investigation of fluid flow and heat transfer in a doublet enhanced geothermal system with CO2 as the working fluid (CO2–EGS)

Thermal performance of a deep borehole heat exchanger: Insights from a synthetic coupled heat and flow model

Most industrial areas, especially oilfield operations and geothermal reservoirs, deal with varying viscosities in multicomponent electrolyte solutions. An accurate estimate of this property as a function of pressure, temperature, and varying salt concentrations is highly desirable. Although a number of empirical correlations have already been developed, they are still limited to single electrolyte solutions and can only operate over specified temperature and pressure ranges. In this study, a highly accurate model based on an adaptive network-based fuzzy inference system was developed, mainly devoted to dynamic viscosity prediction in aqueous multicomponent chloride solutions. Crisp input data were transformed into fuzzy sets employing the subtractive clustering algorithm with an effective radius optimized by a hybrid of genetic algorithm and particle swarm optimization technique. Comparing the model with thousands of experimental data concluded in squared correlation coefficient (R2) of 0.9986 and an aver...

Assessing the Dynamic Viscosity of Na–K–Ca–Cl–H2O Aqueous Solutions at High-Pressure and High-Temperature Conditions

In several areas of the North German Basin, saline water comes close to, or even reaches the surface. Available data from wells indicate that brine stratification is under unstable conditions in the deeper underground. In order to analyse the possible transport mechanisms, 3D thermohaline simulations have been carried out for two different scenarios. The 3D regional model (230×330 km) indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands. In addition, a smaller scale model (10×10 km) has been constructed with a grid resolution accounting for possible convective flow. The results indicate that convective flow may play a dominant role in areas with minor topography. In summary, the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces.

V. Clausnitzer

Papers

Fluid-dynamics driving saline water in the North East German Basin

Deep reaching fluid flow close to convective instability in the NE German basin—results from water chemistry and numerical modelling