Geochemical monitoring in the Hontomín (Burgos, Spain) injection site: preliminary results and perspectives

CO2 capture and storage (CCS) projects are presently developed to reduce the emission of anthropogenic CO2 into the atmosphere. CCS technologies are expected to account for the 20% of the CO2 reduction by 2050. One of the main concerns of CCS is whether CO2 may remain confined within the geological formation into which it is injected since post-injection CO2 migration in the time scale of years, decades and centuries is not well understood. Theoretically, CO2 can be retained at depth i) as a supercritical fluid (physical trapping), ii) as a fluid slowly migrating in an aquifer due to long flow path (hydrodynamic trapping), iii) dissolved into ground waters (solubility trapping) and iv) precipitated secondary carbonates. Carbon dioxide will be injected in the near future (2012) at Hontomín (Burgos, Spain) in the frame of the Compostilla EEPR project, led by the Fundación Ciudad de la Energía (CIUDEN). In order to detect leakage in the operational stage, a pre-injection geochemical baseline is presently being developed. In this work a geochemical monitoring design is presented to provide information about the feasibility of CO2 storage at depth.

Hydrogeochemistry of surface and spring waters in the surroundings of the CO2 injection site at Hontomín–Huermeces (Burgos, Spain)

In this paper the very first geochemical and isotopic data related to surface and spring waters and dissolved gases in the area of Hontomín–Huermeces (Burgos, Spain) are presented and discussed. Hontomín–Huermeces has been selected as a pilot site for the injection of pure (>99%) CO2. Injection and monitoring wells are planned to be drilled close to 6 oil wells completed in the 1980s for which detailed stratigraphical logs are available, indicating the presence of a confined saline aquifer at the depth of about 1500 m into which less than 100,000 tons of iquid CO2 will be injected, possibly starting in 2013. The chemical and features of the spring waters suggest that they are related to a shallow hydrogeological system as the concentration of the Total Dissolved Solids approaches 800 mg/L with a Ca2+(Mg2+)-HCO3− composition, similar to that of the surface waters. This is also supported by the oxygen and hydrogen isotopic ratios that have values lying between those of the Global and the Mediterranean Meteoric Water Lines. Some spring waters close to the oil wells are haracterized by relatively high concentrations of NO3− (up to 123 mg/L), unequivocally suggesting an anthropogenic source that adds to the main water–rock interaction processes. The latter can be referred to Ca-Mg-carbonate and, at a minor extent, Al-silicate dissolution, being the outcropping sedimentary rocks characterized by Palaeozoic to Quaternary rocks. Anomalous concentrations of Cl−, SO42−, As, B and Ba were measured in two springs discharging a few hundred meters from the oil wells and in the Rio Ubierna. These contents are significantly higher than those of the whole set of the studied waters and are possibly indicative of mixing processes, although at very low extent, between deep and shallow aquifers. No evidence of deep-seated gases interacting with the Hontomín–Huermeces waters was recognized in the chemistry of the disolved gases. This is likely due to the fact that they are mainly characterized by an atmospheric source as highlighted by the high contents of N2, O2 and Ar and by N2/Ar ratios that approach that of ASW (Air Saturated Water) and possibly masking any contribution related to a deep source. Nevertheless, significant concentrations (up to 63% by vol.) of isotopically negative CO2 (<−17.7‰ V-PDB) were found in some water samples, likely related to a biogenic source. The geochemical and isotopic data of this work are of particular importance when a monitoring program will be established to verify whether CO2 leakages, induced by the injection of this greenhouse gas, may be affecting the quality of the waters in the shallow hydrological circuits at Hontomín–Huermeces. In this respect, carbonate chemistry, the isotopic carbon of dissolved CO2 and TDIC (Total Dissolved Inorganic Carbon) and selected trace elements can be considered as useful parameters to trace the migration of the injected CO2 into near-surface environments.

CO2 soil flux baseline at the technological development plant for CO2 injection at Hontomin (Burgos, Spain)

From the end of 2013 and during the following two years, 20 kt of CO2sc are planned to be injected in a saline reservoir (1500 m depth) at the Hontomín site (NE Spain). The target aquifers are Lower Jurassic limestone formations which are sealed by Lower Cretaceous clay units at the Hontomín site (NE Spain). The injection of CO2 is part of the activities committed in the Technology Development phase of the EC-funded OXYCFB300 project (European Energy Program for Recovery – EEPR, http://www.compostillaproject.eu), which include CO2 injection strategies, risk assessment, and testing and validating monitoring methodologies and techniques. Among the monitoring works, the project is intended to prove that present-day technology is able to monitor the evolution of injected CO2 in the reservoir and to detect potential leakage. One of the techniques is the measurement of CO2 flux at the soil–atmosphere interface, which includes campaigns before, during and after the injection operations. In this work soil CO2 flux measurements in the vicinity of oil borehole, drilled in the eighties and named H-1 to H-4, and injection and monitoring wells were performed using an accumulation chamber equipped with an IR sensor. Seven surveys were carried out from November 2009 to summer 2011. More than 4000 measurements were used to determine the baseline flux of CO2 and its seasonal variations. The measured values were low (from 5 to 13 g m−2 day−1) and few outliers were identified, mainly located close to the H-2 oil well. Nevertheless, these values cannot be associated to a deep source of CO2, being more likely related to biological processes, i.e. soil respiration. No anomalies were recognized close to the deep fault system (Ubierna Fault) detected by geophysical investigations. There, the CO2 flux is indeed as low as other measurement stations. CO2 fluxes appear to be controlled by the biological activity since the lowest values were recorded during autumn-winter seasons and they tend to increase in warm periods. Two reference CO2 flux values (UCL50 of 5 g m−2 d−1 for non-ploughed areas in autumn–winter seasons and 3.5 and 12 g m−2 d−1 for in ploughed and non-ploughed areas, respectively, in spring–summer time, and UCL99 of 26 g m−2 d−1 for autumn–winter in not-ploughed areas and 34 and 42 g m−2 d−1 for spring–summer in ploughed and not-ploughed areas, respectively) were calculated. Fluxes higher than these reference values could be indicative of possible leakage during the operational and post-closure stages of the storage project.

Water chemistry at Hontomín-Huermeces (Burgos, Spain): insights for a pre-, intra- and post-CO2 injection geochemical monitoring.

In this study, the very first geochemical and isotopic data related to surface and spring waters and dissolved gases in the area of Hontomín-Huermeces (Burgos, Spain) are presented and discussed. Hontomín-Huermeces was selected as a pilot site for the injection of pure (>99 %) CO2. Injection and monitoring wells are planned to be drilled close to 6 oil wells completed in the 1980’s. Stratigraphical logs indicate the presence of a confined saline aquifer at the depth of about 1,500 m into which less than 100,000 tons of liquid CO2 will be injected, possibly starting in 2013. The chemical and isotopic features of the spring waters suggest the occurrence of a shallow aquifer having a Ca2+(Mg2+)-HCO3- composition, relatively low salinity (Total Dissolved Solids _800 mg/L) and a meteoric isotopic signature. Some spring waters close to the oil wells are characterized by relatively high concentrations of NO3- (up to 123 mg/L), unequivocally indicating anthropogenic contamination that adds to the main water-rock interaction processes. The latter can be referred to Ca-Mg-carbonate and, at a minor extent, Al-silicate dissolution, being the outcropping sedimentary rocks characterized by Palaeozoic to Quaternary rocks. Anomalous concentrations of Cl-, SO42-, As, B and Ba were measured in two springs discharging a few hundreds meters from the oil wells and in the Rio Ubierna, possibly indicative of mixing processes, although at very low extent, between deep and shallow aquifers. Gases dissolved in spring waters show relatively high concentrations of atmospheric species, such as N2, O2 and Ar, and isotopically negative CO2 (<-17.7 h V-PDB), likely related to a biogenic source, possibly masking any contribution related to a deep source. The geochemical and isotopic data of this study are of particular importance when a monitoring program will be established to verify whether CO2 leakages, induced by the injection of this greenhouse gas, may affect the quality of the waters of the shallow Hontomín-Huermeces hydrological circuit. In this respect, carbonate chemistry, the isotopic carbon of dissolved CO2 and TDIC (Total Dissolved Inorganic Carbon) and selected trace elements can be considered as useful parameters to trace the migration of the injected CO2 into near-surface environments.