Reservoir engineering is essential for an appropriate development of geothermal resources. Optimum economic utilization of geothermal reservoirs requires analysis of the geological system together with adequate planning. These include chemical and petropysical reservoir characterisation, reservoir stimulation and modelling as well as understanding of the processes and interaction of the borehole-reservoir system.
Stimulation treatments are an option to enhance the productivity of low permeability geothermal reservoirs by inducing artificial fluid pathways. At GFZ specific stimulation treatments have been developed to enhance the existing permeability; i.e.hydraulic fracturing, thermally induced fracturing and chemical/acid stimulation. In hydraulic stimulation experiments, fluids are injected under high pressure into the subsurface rocks to create new fractures or extend existing fractures.
Effective energy production from geothermal reservoirs requires that the physical properties of the host rock have to be characterized as precisely as possible. Additionally, rock physical experiments provide a valuable complementary method to investigate particular processes associated with mechanical and thermodynamic changes induced during operation. The results of such investigations improve the outcome of hydro-thermo-mechanical-chemical (HTMC) simulation codes in order to derive statements on reservoir productivity, sustainability, and best-practice operation.
An appropriate numerical model is important for planning the well path and fracture design, interpreting hydraulic tests and stimulations, and predicting reservoir behavior during geothermal power production. Such models should include: (i) the reservoir geology and structure, (ii) the geometry of wells and fractures and (iii) the hydraulic, thermal, mechanical and chemical (HTMC) conditions of the reservoir and fractures generated due to changes in reservoir conditions.
Chemical reactions between the geothermal fluid and either plant materials or reservoir rocks can damage the reservoir (by clogging the pores) as well as the plant components (by corrosion). Therefore, geochemical processes are investigated in field and lab scale. Lab experiments focus on mineral formation processes induced by changes in p-T-conditions in synthetic brines. In the field, insitu parameters are measured online and fluid samples are collected and analyzed. Additional well tests (e.g. tracer tests) help to understand the controls on sustainability and efficiency.