New Experimental Equipment Recreating Geo-Reservoir Conditions in Large, Fractured, Porous Samples to Investigate Coupled Thermal, Hydraulic and Polyaxial Stress Processes.

Use of the subsurface for energy resources (enhanced geothermal systems, conventional and unconventional hydrocarbons), or for storage of waste (CO2, radioactive), requires the prediction of how fluids and the fractured porous rock mass interact. The GREAT cell (Geo-Reservoir Experimental Analogue Technology) is designed to recreate subsurface conditions in the laboratory to a depth of 3.5 km on 200 mm diameter rock samples containing fracture networks, thereby enabling these predictions to be validated. The cell represents an important new development in experimental technology, uniquely creating a truly polyaxial rotatable stress field, facilitating fluid flow through samples, and employing state of the art fibre optic strain sensing, capable of thousands of detailed measurements per hour. The cell's mechanical and hydraulic operation is demonstrated by applying multiple continuous orientations of principal stress to a homogeneous benchmark sample, and to a fractured sample with a dipole borehole fluid fracture flow experiment, with backpressure. Sample strain for multiple stress orientations is compared to numerical simulations validating the operation of the cell. Fracture permeability as a function of the direction and magnitude of the stress field is presented. Such experiments were not possible to date using current state of the art geotechnical equipment.

Development of a regional hydrologic soil model and application to the Beerze--Reusel drainage basin.

The soil compartment is an important interface between the atmosphere and the subsurface hydrosphere. In this paper a conceptual approach for regional hydrologic soil modelling (RHSM) is presented, which provides two important qualities for modelling. First, the soil compartment is directly coupled to the atmosphere via the land surface and to the aquifers. Second, extremely fine (5cm vertical) resolutions of the soil system can be realized at regional scales (several hundreds of km(2)). This high-resolution modelling could be achieved by parallel computation techniques. The RHSM approach is applied to the Beerze-Reusel drainage basin, which belongs to the Meuse River basin. Moisture transport in the soil system was calculated with extremely high vertical resolution at a regional scale based on rainfall-evaporation data for the year 2000. As a result, highly resolved regional groundwater recharge pattern addressing the heterogeneity of soil systems could be determined.

Future climate scenarios and rainfall--runoff modelling in the Upper Gallego catchment (Spain).

Global climate change may have large impacts on water supplies, drought or flood frequencies and magnitudes in local and regional hydrologic systems. Water authorities therefore rely on computer models for quantitative impact prediction. In this study we present kernel-based learning machine river flow models for the Upper Gallego catchment of the Ebro basin. Different learning machines were calibrated using daily gauge data. The models posed two major challenges: (1) estimation of the rainfall-runoff transfer function from the available time series is complicated by anthropogenic regulation and mountainous terrain and (2) the river flow model is weak when only climate data are used, but additional antecedent flow data seemed to lead to delayed peak flow estimation. These types of models, together with the presented downscaled climate scenarios, can be used for climate change impact assessment in the Gallego, which is important for the future management of the system.

3-D numerical evaluation of density effects on tracer tests.

In this paper we present numerical simulations carried out to assess the importance of density-dependent flow on tracer plume development. The scenario considered in the study is characterized by a short-term tracer injection phase into a fully penetrating well and a natural hydraulic gradient. The scenario is thought to be typical for tracer tests conducted in the field. Using a reference case as a starting point, different model parameters were changed in order to determine their importance to density effects. The study is based on a three-dimensional model domain. Results were interpreted using concentration contours and a first moment analysis. Tracer injections of 0.036 kg per meter of saturated aquifer thickness do not cause significant density effects assuming hydraulic gradients of at least 0.1%. Higher tracer input masses, as used for geoelectrical investigations, may lead to buoyancy-induced flow in the early phase of a tracer test which in turn impacts further plume development. This also holds true for shallow aquifers. Results of simulations with different tracer injection rates and durations imply that the tracer input scenario has a negligible effect on density flow. Employing model cases with different realizations of a log conductivity random field, it could be shown that small variations of hydraulic conductivity in the vicinity of the tracer injection well have a major control on the local tracer distribution but do not mask effects of buoyancy-induced flow.