Publication Date:
2024-05-09
Description:
CO2 Capture & Storage (CCS) is presently one of the most promising technologies
for reducing anthropogenic emissions of CO2 . Among the several potential geologi-
cal CO2 storage sites, e.g. depleted oil and gas field, unexploitable coal beds, saline
aquifers, the latter are estimated to have the highest potential capacity (350-1000 Gt
CO2 ) and, being relatively common worldwide, a higher probability to be located
close to major CO2 anthropogenic sources. In these sites CO2 can safely be retained
at depth for long times, as follows: a) physical trapping into geologic structures; b) hy-
drodynamic trapping where CO2(aq) slowly migrates in an aquifer, c) solubility trap-
ping after the dissolution of CO2(aq) and d) mineral trapping as secondary carbon-
ates precipitate. Despite the potential advantages of CO2 geo-sequestration, risks of
CO2 leakage from the reservoir have to be carefully evaluated by both monitoring
techniques and numerical modeling used in “CO2 analogues”, although seepage from
saline aquifers is unlikely to be occurring. The fate of CO2 once injected into a saline
aquifer can be predicted by means of numerical modelling procedures of geochemical
processes, these theoretical calculations being one of the few approaches for inves-
tigating the short-long-term consequences of CO2 storage. This study is focused on
some Italian deep-seated (〉800 m) saline aquifers by assessing solubility and min-
eral trapping potentiality as strategic need for some feasibility studies that are about
to be started in Italy. Preliminary results obtained by numerical simulations of a geo-
chemical modeling applied to an off-shore Italian carbonatic saline aquifer potential
suitable to geological CO2 storage are here presented and discussed. Deep well data,
still covered by industrial confidentiality, show that the saline aquifer, includes six
Late Triassic-Early Jurassic carbonatic formations at the depth of 2500-3700 m b.s.l.
These formations, belonging to Tuscan Nappe, consist of porous limestones (mainly
calcite) and marly limestones sealed, on the top, by an effective and thick cap-rock
(around 2500 m) of clay flysch belonging to the Liguride Units. The evaluation of the
potential geochemical impact of CO2 storage and the quantification of water-gas-rock
reactions (solubility and mineral trapping) of injection reservoir have been performed
by the PRHEEQC (V2.11) Software Package via corrections to the code default ther-
modynamic database to obtain a more realistic modelling. The main modifications to
the Software Package are, as follows: i) addition of new solid phases, ii) variation
of the CO2 supercritical fugacity and solubility under reservoir conditions, iii) addi-
tion of kinetic rate equations of several minerals and iv) calculation of reaction sur-
face area. Available site-specific data include only basic physical parameters such as
temperature, pressure, and salinity of the formation waters. Rocks sampling of each
considered formation in the contiguous in-shore zones was carried out. Mineralogy
was determined by X-Ray diffraction analysis and Scanning Electronic Microscopy
on thin sections. As chemical composition of the aquifer pore water is unknown, this
has been inferred by batch modeling assuming thermodynamic equilibrium between
minerals and a NaCl equivalent brine at reservoir conditions (up to 135 ̊C and 251
atm). Kinetic modelling was carried out for isothermal conditions (135 ̊C), under a
CO2 injection constant pressure of 251 atm, between: a) bulk mineralogy of the six
formations constituting the aquifer, and b) pre-CO2 injection water. The kinetic evolu-
tion of the CO2 -rich brines interacting with the host-rock minerals performed over 100
years after injection suggests that solubility trapping is prevailing in this early stage
of CO2 injection. Further and detailed multidisciplinary studies on rock properties,
geochemical and micro seismic monitoring and 3D reservoir simulation are necessary
to better characterize the potential storage site and asses the CO2 storage capacity.
Description:
Published
Description:
Vienna (Austria)
Description:
2.4. TTC - Laboratori di geochimica dei fluidi
Description:
open
Keywords:
CO2 storage
;
Geochemical modeling
;
01. Atmosphere::01.01. Atmosphere::01.01.02. Climate
;
01. Atmosphere::01.01. Atmosphere::01.01.06. Thermodynamics
;
03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling
;
03. Hydrosphere::03.02. Hydrology::03.02.03. Groundwater processes
;
03. Hydrosphere::03.04. Chemical and biological::03.04.03. Chemistry of waters
;
04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration
;
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
Abstract
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