Geochemistry of a continental saline aquifer for CO2 sequestration: The Guantao formation in the Bohai Bay Basin, North China

The Neogene Guantao formation in the Beitang sag in the Bohai Bay Basin (BBB) of North China, a Mesozoic-Cenozoic sedimentary basin of continental origin, has been chosen as a candidate for a pilot field test of CO2 sequestration. Hydrogeological and geochemical investigations have been carried out to assess its suitability, taking advantage of many existing geothermal wells drilled to 2000 m or greater depths. Water samples from 25 wells and drill cores of three sections of the Guantao formation were collected for measurements of mineralogy, water chemistry and isotopes (delta O-18, delta D, delta C-13, C-14). Formation temperature estimated by chemical geothermometry is in the range of 60-80 degrees C. Geochemical modeling of water-rock-CO2 interaction predicts a strong geochemical response to CO2 injection. Besides the elevated porosity (33.6-38.7%) and high permeability (1150-1980 mD) of the Ng-III formation and a favorable reservoir-caprock combination, it is also found that the formation contains carbonates that will react with CO2 after injection. The low salinity (TDS < 1.6 g/L) offers high CO2 solubility. The C-14 age of the formation water indicates a quasi-closed saline aquifer system over large time scales, the lateral sealing mechanism for CO2 sequestration requires further investigation. The CO2 storage capacity of the Guantao formation within the Beitang sag is estimated to be 17.03 Mt, assuming pure solubility trapping. (C) 2012 Elsevier Ltd. All rights reserved.