The Soultz project is a long-term research project aiming to develop a new kind of
geothermal energy. It is an ambitious project, not only in scientific and industrial
terms but also in terms of its organisation. The numerous stages and partners
involved mean that it is a fairly complex programme spread over a long period of time.
The EGS (Enhanced Geothermal Systems) principle also called HFR (Hot Fractured Rocks)
aims to extract the heat contained in deep-seated rock (between 3,000 and 6,000m) by
circulating water through a large capacity natural heat exchanger. This can be
created by hydraulic and/or chemical stimulation of the permeability of natural
fractures in hydrothermally active regions where deep rocks are permeable enough for
the temperature to increase more quickly with depth than normal due to regional
convective loops (200°C at about 5,000m deep at Soultz). The search for deep hot
fractured massif led to the selection of a site in the Rhine Valley which
corresponds, from the geological point of view, to a graben zone. The region chosen
was Soultz, 50 km north-west of Strasbourg, a zone already wellknown for its thermal
springs and with a well-established geology because of oil extraction in the past (it
is close to Pechelbronn oil field).
The objective of the current works is to build a pilot plant aiming to demonstrate
that it is possible, using an experimental loop, to develop an extraction process which:
- is a net energy producer, i.e. producing much more than what is consumed by the
auxiliaries;
- is stable over a long period (several years);
- constitutes a technical system free from gaps which has no prohibitive impact on
the environment;
- is designed so that the technology will be rapidly standardised and cost-effective.
The results obtained today: drilling of the three deep wells and preliminary
underground hydraulic tests. After five years of progresses, the construction of the
underground part of the pilot is now almost finished.
Drilling works, which ended in April 2004, made possible to verify the geotechnical
conditions, particularly the resistance of the wells to breakouts. In order to limit
risks of hydraulic "short-circuits", the extremities of the wells are, as planned,
650m to 700m apart, but because directional drilling was used, the well heads are
only 6m apart.
Works for the connections of the wells on the surrounding massif, together with the
development of the inter-well exchange zone, have progressed enough for the start of
medium-term circulation tests (5 months) to be engaged in July 2005. These provided a
first evaluation of the inter-wells exchanger(s) and of the surrounding natural
reservoir’s behaviour particularly with regard to the evaluation of the future
improvements required for efficient pumping and the likely kinetics of cooling the
environment.
During the medium term tests performed in 2005 some 165,000m3 and 40,000m3 of brine
were produced respectively from GPK2 and GPK4 using buoyancy effect, keeping # 8 bars
well head pressure in order to avoid scaling risk. Consequently about 210,000m3 were
reinjected in the central well GPK3.
During the vast majority of time:
- GPK2 produced F2 # 12l/s with ΔP2#12bars (Productivity index # 1l/s/bar);
- GPK4 produced F4 # 3l/s with ΔP4#9bars (Productivity index # 0.35l/s/bar);
- F3=(F2+F4), i.e. # 15l/s, was re-injected in GPK3 with a bottom hole overpressure
#60 bar (Injectivity index # 0.25l/s/bar) which generated some minor micro-seismic
activity.
A tracer test shown that after about 5 months of circulation, some 25% of the
fluorescein injected in GPK3 was recovered in the production of GPK2 and only # 1.8%
in the one of GPK4.
Targets for future: Short term
From the tests performed in 2005, it appears today that the distribution of natural
permeabilities in the deep fractured system at Soultz is the leading factor for the
wells productivities/injectivities. Consequently the quality of the connections
developed between the wells and the far field network of natural permeable fractures
is of major interest. The main targets being both to produce maximum flow rates with
minimum pumping power and to get the most possible stable production temperatures it
will be necessary to carefully consider the future role which could be devoted to the
inter-wells heat exchanger for EGS operations in the context of "Soultz type" systems.
During the next months this will lead us to try to develop for the best the
connections between GPK4 and the far field natural reservoir. Then, depending from
the results of some planned investigations, we will try to address the question of
the poor injectivity of GPK3 (and associated risk of micro-seismic nuisances) with an
appropriate strategy towards a general optimisation of the future conditions of
exploitation.
Targets for future: Medium term
The main objective of the next step is the construction of a pilot plant producing
electricity.
Particular attention is already focused on the following points:
- Pumps and power required for production and reinjection;
- Possible adverse environmental effects;
- Predictive maintenance of facilities;
- Cooling system;
- Hydraulic and thermal performances of the system;
- Thermodynamic conversion cycles.
A preliminary evaluation of the results will be made, before validation of the
decision to build a first electrical conversion unit aiming to produce early 2007
some 1.5MW then to extend that production towards its optimal value.
Targets for future: Long term
Industrial test phase (industrial prototype) – by 2010
If the technical and economic hypotheses investigated in the preceding phase are
validated, the objective will be to construct a first prototype module, on an
industrial scale in terms of size and structure, then to test it, before to improve
performances and arrange for large-scale production of standard modules; the power
would be in a ratio of four to five with that of the pilot (25MWe).
Industrial development and distribution phase – by 2015 and after …
This will consist, at each production site, of combinations of modules suitable for
adaptation to the best local conditions of exploitation. Substantial price reductions
will be achieved by standardising the modules and plant management as it has already
been demonstrated at standard geothermal extraction sites (for example in Italy and
Indonesia).
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