Accueil > EGW 2018 : 6th European Geothermal Workshop > Abstracts > Session 3 : Operating of Geothermal Systems > Session 3 : Oral Presentations

Session 3 : Oral Presentations


The in-situ stimulation experiment at the Grimsel test site – an overview

Florian Amann

The Swiss Energy Strategy 2050 (ES2050) plans to replace nuclear electricity production with an increased utilization of different sources of new renewable energy and sets a target of 7% national electricity supply from Deep Geothermal Energy (DGE) by 2050, corresponding to 4.4 TWh per year and over 500 MWe installed capacity. To reach the ES2050 target, Switzerland will need to install on average 20 MWe per year of additional capacity of electricity production from DGE between 2025 and 2050. A capacity of 20 MWe requires the circulation of over 220 l/s of water at temperatures of 170-190°C, commonly found at 4-6 km depths in Switzerland. As hydrothermal water is scarse and difficult to locate, deep reservoirs will need to be created in hot crystalline basement rock (EGS), safely and at competitive costs.

The ISC project is a decameter in-situ experiment that is currently performed at the Grimsel Test Site (GTS) at a depth of approximately 480m and within crystalline rock. The ISC experiment includes controlled fault slip and hydraulic fracturing experiments at an intermediate scale (i.e. 20*20*20m), which allows high resolution monitoring of the evolution of pore pressure in the stimulated fault zone and the surrounding rock matrix, fault dislocations including shear and dilation, and micro-seismicity in an exceptionally well characterized structural setting.

From 2015 to 2017 we performed an intense characterization and preparation phase that included :

1) Stress measurements using various methods such as hydraulic fracturing, overcoring and hydraulic jacking,

2) Geological characterization using borehole logging, tunnel mapping, Ground Penetration Radar and active seismic measurements,

3) Pre-stimulation hydraulic characterization,

4) Tracer tests using dyes, salt and DNA nanoparticles.

5) installation of monitoring equipment including FBG fibre optics sensors and distributed fibre optics for strain measurements, distributed fibre optics temperature measurements, tiltmeters, micro-seismic surface and borehole sensors, pore pressure sensors and surface extensometers.

In February 2017 we performed a series of fault-slip experiments (i.e. 6 experiments) on interconnected faults adjacent to two injection boreholes. During the test we used one injection borehole to inject water at high pressures (rates up to 35 l/min) and the second injection boreholes to monitor the pressure propagation.

Subsequent to the fault-slip experiments we performed an intense phase of post-stimulation hydraulic characterization. In Mai 2017 we performed a series of five hydraulic fracturing tests within test intervals that were free of natural fractures. Two injection fluids were used : pure water and a Xanthan-Salt-Water mixture with a viscosity of 30-40cp and an electric conductivity of 1800-2000 microS/m.

Energetic balancing of the cyclic operation of a high temperature aquifer storage

Jörg Meixner, Martin Jägle, Ingrid Stober, Thomas Kohl

The private sector energy consumption in Germany rather constantly accounts for about 50 % of the final energy production. More than 80% of this fraction is furthermore attributable to thermal energy. Thus high innovation and saving potentials arise for the heat market. Both are strongly required to meet national and international climate protection goals. A steady increase in renewable energies such as solar thermal systems helps to decentralize the heat market and to decrease CO2 emissions. But common to many renewables is a seasonally phase-shifted supply and demand function. Heat demand is lowest in the summer months where heat production rates, e.g. of a solar thermal plant, commonly is peaking.

Cyclic storage of surplus heat in the summer is one possibility to close gaps in heat supply in the winter that are currently filled by the use of fossil fuels. Aquifer thermal energy storage systems, ATES, focus on storage and recovery of thermal energy by extraction and injection of groundwater from shallow seated aquifers (< 100 m). Because their applications are limited to areas with low groundwater flow velocities shallow seated Tertiary and Quaternary aquifers in the Upper Rhine Graben, URG, in Germany seem to be unsuitable for this technique. Mesozoic sediments, however, still are of interest since they locally occur in depth ranges of 500 – 1500 m, in suitable PT ranges for high temperature aquifer storage operations. Because pilot plants and field data are missing in the URG, a feasibility study based on geological and finite element, FE, modelling was conducted to 1) simulate a solar thermal heating plant that is coupled with a deep geothermal aquifer storage and 2) to assess the overall energy balances of different modes of storage operation. Various operating modes of the aquifer storage have been considered. “Static” scenarios with 175-day storage and production phases and constant volumetric flows allow quantification of maximum installed capacities, energies, and efficiencies achievable with the cyclic storage operation. “Dynamic” scenarios consider natural fluctuations of the global radiation during heat generation of a solar thermal plant. Sub-models for different volumetric flows, heat extraction rates, formation permeabilities, and borehole designs highlight sensitivity of individual, may site-specific, system parameters on the hydrogeological, geothermal, and economic outcomes of the FE modellings.

Following the maximum scenario of a “static” storage operation, up to 26 GWht per year can be produced from a deep geothermal aquifer storage (Figure 1) in the heating phase. In this scenario the annual heat demand of about 1000 households can be covered. The produced thermal energy corresponds to a heating oil equivalent of about 2.6 Mio l, which would need to be used to cover the annual heat demand.

The efficiency of different modes of the storage operation can be quantified by the recovery factor, the ratio between the stored and produced thermal energy. The modeled efficiencies in the static and dynamic models vary between 50 and 85 % and therefore range in the same order of magnitude as 1) the results obtained in comparable studies for shallow ATES systems (Schout et al., 2014 ; Xiao et al., 2016 ; e.g. Major et al., 2018) and 2) measured ones at the few demonstration projects in northern Germany (Sanner et al., 2005 ; Kabus et al., 2009).

Our results show, that cyclic operations of deep aquifer storages have the potential : 1) to store surplus heat in the subsurface with minor energetic losses ; 2) to fill gaps in heat supply in the winter by surplus heat of the summer, which significantly increases the overall efficiency of different heat generation techniques ; 3) to decrease the oil or gas consumption rate in the heating periods ; 4) to reduce the CO2 emissions related to the use of fossil energies.

Turkey’s Geothermal Success

Orhan Mertoglu, Nilgun Basarir

Turkey has achieved important geothermal developments in last 15 years. Since the 1960’s, more than 240 geothermal fields have been discovered in Turkey.

Geothermal direct-use applications have reached 3322 MWt geothermal heating including district heating (1033 MWt), 4,3 million m2 greenhouse heating (820 MWt), thermal facilities, hotels etc heating 440 MWt, balneological use 1055 MWt, agricultural drying 1,6 MWt) and heat pump applications (42,8 MWt).

Geothermal electricity production is 1200 MWe (Aydin-Germencik, Aydin-Salavatli, Manisa-Salihli, Manisa-Alaşehir, Denizli-Kizildere, Aydin-Hidirbeyli, Canakkale-Tuzla, Aydın-Pamukören, Aydin- Gumuskoy and others) as of September 2018. Food grade liquid carbon dioxide and dry ice production recovery plant (400.000 tons/year) as factories are integrated to the Kizildere and Salavatli geothermal power plants.

Recently, Buharkent (Aydin) geothermal power plant has been started to operate with 13,8 MWe install capacity, which is the first and single application in terms of geothermal electricity production from a non-artesian geothermal field inTurkey. The static water level is at - 260 m depth. The leaving geothermal water is transferred to the reinjection wells without additional pumping by means of vacuum condition at the wellhead (as a free reinjection).

The first action of the issued geothermal law and incentives was done in the World Geothermal Congress 2005 in Antalya which contributed to the increase in geothermal electricity production investments within Turkish private sector. Beside of the hydrothermal system utilization, Turkey shall give emphasize on EGS systems for future projections.

The Turkish Geothermal Association are giving emphasise and advise on the continuing of the feed in tariff which will end at the end of 2020. With big probability it would continue with a little bit lower feed in tariff.

Geothermal power plants are base load plants. The highest value in capacity factor is 99,4% in Germencik geothermal power plant (44,7 MWe).

The total hydrothermal possible theoretical geothermal heat potential is 60.000 MWt according to heat flow maps, measured well depth temperatures and calculations made for 4 km depth.

Turkey’s geothermal technical and economical electricity production potential (hydrothermal, 0-4 km) can be estimated as 2500 MWe (20 billion kWh/year) with existing 10,5 USDcent/kWh incentive and 10 years purchase guarantee.

The technical and economical EGS geothermal electricity production potantial has been projected as 15.000 MWe if the 15 USDcent/kWh incentive with minimum 15 year purchase guarantee would be possible.

The operational capacities of some of the city based geothermal district heating systems (GHDS) existing in Turkey are as follows :

Gönen (Commissioned : 1987, 3400 residences, geoth. fluid temperature is 80°C),
Simav (1991, 12000 residences, 120°C),
Kirsehir (1994, 1900 residences, 57°C),
Kizilcahamam (1995, 2500 residences, 80°C),
Izmir (1996, 37.000 residences, 115-142°C), (250 MWt, 0,5 MWe geothermal air-conditioning)
Sandikli (1998, 11000 residences, 70°C),
Afyon (1996, 14000 residences, 95°C),
Kozakli (1996, 3000 residences, 90°C),
Diyadin (1999, 570 residences, 70°C),
Edremit (2003, 6000 residences, 60 °C)

It is known that the CO2 in the geothermal fields in Turkey, are formed mostly by the marble and karbonated rocks due to the effect of the water and heat.

The CO2 emission amount is more at the fault and fracture zones. As it can be understood, this procedure is not under our initiative. It is a natural discharge of CO2 and is independent to the existence of geothermal power plants. An important portion of CO2 is emitted to the atmosphere from the geothermal power plants after electricty is produced.

Roughly 50-70 % decreament in the CO2 amount in 10 years in the geothermal fields in Turkey has been obtained. Generally, the CO2 emission varies between 398-442 gr/kWh (average) in Turkey. The decreament continues. The reasons of the decline of CO2 in the geothermal fields can be explained as the following :

1)Very less CO2 amount in the high pressure reinjected water, reinjection is compulsory because of maintenance and sustainabilitiy of the reservoir and protection of the environment
2) The natural recharge of the geothermal reservoir is composed mostly from rain water
3) Geothermal fluid production amount is much more than the natural recharge amount
As the result of oral communication with many geothermal power plant operators in Turkey, this decrease in CO2 in geothermal reservoirs has been recognised.

As a natural result of CO2 decrease in the geothermal fields ; The downhole pump usage in the geothermal fields will be increased .

Existing CO2 in the geothermal fluid is the advantage for the artesianic well flow but it is a disadvantgae for the power plant electricity generation.

The 1200 MWe geothermal electricity production install capacity is composed of about 800 MWe binary cycle geothermal power plants, ORC and air cooled condenser (20% house consumption) and about 400 MWe flash steam geothermal power plant (double flash, triple flash and integrated with the binary cycle plants, water cooled condenser (10-20% house consumption)) power plants are running technical and economical feasible conditions in Turkey.

11 décembre 2018