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

• Published in: International journal of greenhouse gas control 2013-05, Vol.14, p.151-168
• Main Authors: Nisi, Barbara, Vaselli, Orlando, Tassi, Franco, de Elio, Javier, Huertas, António Delgado, Mazadiego, Luis Felipe, Ortega, Marcelo F.
• Format: Article
• Language: English
• Subjects: Carbon isotopes; CO2 injection; Dissolved gases; Geochemical monitoring; Hontomín–Huermeces; Trace elements
• ISSN: 1750-5836; 1878-0148
• DOI: 10.1016/j.ijggc.2013.01.012

► A pilot plant to inject CO2 will shortly be installed at Hontomín–Huermeces (HH) (Burgos, Spain). ► First geochemical and isotopic data of the HH surface and ground waters. ► Low TDS and Ca(Mg)-HCO3 chemistry suggests shallow and rapid circulation. ► These data represent a geochemical background for intra- and post-injection monitoring programs. ► Carbon isotopes (CO2 and TDIC) in the Hontomín–Huermeces waters were modeled. 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 1500m into which less than 100,000 tons of liquid 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 800mg/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 characterized by relatively high concentrations of NO3− (up to 123mg/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 dissolved gases. This is likely due to the fact that they are mainly characterized by an atmospheric source as highlighted by the high contents of