| Title | Enhanced Geothermal System in the Lower Carboniferous in the Netherlands – a geological risk and modelling study |
|---|---|
| Authors | Rijkers, van der Hoorn, van Gijtenbeek, Ohmann, Nitters, Bernd Rombout, Spiers, de Zwart |
| Year | 2013 |
| Conference | European Geothermal Conference |
| Keywords | Lower Carboniferous, heat demand, Enhanced Geothermal System, hydraulic stimulation, geological risks, geothermal modelling, business case, SPOT |
| Abstract | The objective of this study is to design a deep geothermal heat exchanger for the Parenco paper mill and to quantify the risk in geothermal flow. The study area is geologically located at the northern flank of the Maasbommel High where the top of the Early Carboniferous (Dinantien) limestone reservoir is recognized at a depth of 4300 m. Two scenarios have been investigated: (1) natural permeability system from karst/geological faults and (2) EGS subsurface heat exchanger with shear or propped fractures. HP-HT laboratory tests were performed with analogue rock samples from the Ardennes area to evaluate the geomechanical and geohydrological behavior and to model the hydraulic behavior of the fractures. A temperature of 170 ºC is calculated from the regional geothermal heat flow in combination with a model of heat conductivities of all overlying formations. Laboratory testing, geological mapping and geo-thermal modeling are carried out to design a geothermal system in the Early Carboniferous limestone. Shear fracturing was eventually not taken into consideration due to expected low differential earth stresses. Hydraulic fracturing was modeled with FracPro PT & MFrac and flow and heat transport through the resulting fracture geometries was modeled with reservoir simulator TOUGH2. The geothermal scenario to extract heat from natural permeability in karst zones and geological faults has a relative high risk profile that is caused by the poor quality of the available seismic data and the absence of wells to the target formation. However, the geological concept is proven in the Californië geothermal project near the eponymous village in the South of the Netherlands, in the same reservoir (Fig. 1). The geological risk of the propped EGS is low but system is significantly more expensive due to high costs of high quality proppant and hydraulic gel that are recommended because of the expected high in situ earth stress (35 MPa), temperature (T> 180 C) and rock strength ( c=50 MPa). Further investigations and 3D seismic data are needed to lower the risk profile of the geothermal project. |