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The pre-feasibility assessment of Castelnuovo (Italy) site for CO2 reinjection in geothermal area: a methodological approach – H2020 GECO Project

Authors:

Abstract

In the framework of Horizon 2020 program, the European Commission funded GECO project that has the overall aim to generate viable, safe and cost-effective technologies for cleaning geothermal power plant exhaust gases to be applied widely at European and global scale. The rationale of GECO project relays on a successful technology recently tested in Iceland at pilot scale, where the gas emissions (mostly steam and CO2) from geothermal power plant were condensed and re-injected in the geothermal reservoir, or turned into commercial products. The GECO partners are committed to characterise 4 different demonstration sites located in Iceland, Italy, Germany and Turkey providing a pre-feasibility assessment of the baseline reservoir conditions and to demonstrate the feasibility of the re-injection (including NGC's) of geothermal fluids. To this latter aim, studies on the re-injection conditions beside the development of efficient and environmentally safe and economic viable methods to purify the geothermal emissions are planned. The Castelnuovo demonstration site is located a few kilometres northeast from Larderello geothermal area where a deep, superheated steam reservoir with 8% of expected NGCs (98% CO2, 2% H2S) is hosted mainly in the metamorphic units and characterised by temperature ranging between 300° and 350°C and pressure up to 70 bar at depths ranging from 4 and 4 km. For the pre-feasibility assessment of the Castelnuovo (Italy) site a geological, geophysical and geochemical integrated approach is proposed. To this aim, different scales and typologies of modelling are ongoing. The area of modelling is about 25 Km x 37 Km in order to include information from the main geological regional structures, which are crucial to increase the accuracy of the reservoir scale models. A first level of modelling produced a geological regional model and a steady state thermal regional model, where existing data and information from structural geologic, geophysical and geochemical field works are embedded. The geometries from geological regional model and the natural thermal state of the underground are acting as input and boundary conditions for the reservoir modelling. The reservoir modelling is the second level of modelling, i.e. local model, and is carried out to assess the exploitation scenario accounting for injection and production. Moreover, at reservoir scale, geochemical modelling of the gas-water-rock interaction during the exploitation is ongoing to predict the fate of reinjected fluids at depth. Laboratory experiments will also provide some constrains on the fluid-rock geochemical reactions expected in the reservoir as consequence of re-injection.
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The pre-feasibility assessment of Castelnuovo (Italy) site for CO2 reinjection in
geothermal area: a methodological approach H2020 GECO Project
Eugenio Trumpy1, Ilaria Baneschi1, Fausto Batini3, Marco Bonini1, Andrea Brogi1, Andrea
Dini1, Gianluca Gola1, 3Laurent Jeannin, Matteo Lelli1, Domenico Liotta1, Francesco Norelli1,
Adele Manzella1, Domenico Montanari1, Giordano Montegrossi1, Andrea Orlando1, Brunella
Raco1, Alessandro Ronconi2, Giovanni Ruggieri1, Alessandro Santilano1, Christine Souque4,
Chiara Boschi1
1CNR, 2MEI, 3Storangy, 4IFPEN
Corresponding author: Tel. +39 050 621 2324, Email: e.trumpy@igg.cnr.it
Keywords:
Geothermal assessment, CO2 sequestration, geological modelling, reservoir simulation
Abstract
In the framework of Horizon 2020 program, the European Commission funded GECO project
that has the overall aim to generate viable, safe and cost-effective technologies for cleaning
geothermal power plant exhaust gases to be applied widely at European and global scale.
The rationale of GECO project relays on a successful technology recently tested in Iceland at
pilot scale, where the gas emissions (mostly steam and CO2) from geothermal power plant
were condensed and re-injected in the geothermal reservoir, or turned into commercial
products.
The GECO partners are committed to characterise 4 different demonstration sites located in
Iceland, Italy, Germany and Turkey providing a pre-feasibility assessment of the baseline
reservoir conditions and to demonstrate the feasibility of the re-injection (including NGC’s) of
geothermal fluids. To this latter aim, studies on the re-injection conditions beside the
development of efficient and environmentally safe and economic viable methods to purify the
geothermal emissions are planned.
The Castelnuovo demonstration site is located a few kilometres northeast from Larderello
geothermal area where a deep, superheated steam reservoir with 8% of expected NGCs (98%
CO2, 2% H2S) is hosted mainly in the metamorphic units and characterised by temperature
ranging between 300° and 350°C and pressure up to 70 bar at depths ranging from 4 and 4
km.
For the pre-feasibility assessment of the Castelnuovo (Italy) site a geological, geophysical and
geochemical integrated approach is proposed. To this aim, different scales and typologies of
modelling are ongoing. The area of modelling is about 25 Km x 37 Km in order to include
information from the main geological regional structures, which are crucial to increase the
accuracy of the reservoir scale models. A first level of modelling produced a geological regional
model and a steady state thermal regional model, where existing data and information from
structural geologic, geophysical and geochemical field works are embedded. The geometries
from geological regional model and the natural thermal state of the underground are acting as
input and boundary conditions for the reservoir modelling. The reservoir modelling is the
second level of modelling, i.e. local model, and is carried out to assess the exploitation scenario
accounting for injection and production. Moreover, at reservoir scale, geochemical modelling
of the gas-water-rock interaction during the exploitation is ongoing to predict the fate of
reinjected fluids at depth. Laboratory experiments will also provide some constrains on the
fluid-rock geochemical reactions expected in the reservoir as consequence of re-injection.
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In addition, based on poro-elasticity model, the setting of fully coupled thermo-hydro-
mechanical models is furthermore performed to evaluate the stress-strain relationship under
injection conditions.
The preliminary results of the of the different kind of modelling will be the used during the
project as base to demonstrate the feasibility of the geothermal fluids reinjection. Moreover,
this integrated approach allows a better understanding of the reservoir baseline conditions at
site level by combining complementary knowledge. The methodology used in the Castelnuovo
site can be easily reused in different plays and context and even for different purpose where
natural reservoir behaviour has to be investigate.
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