A geochemical perspective and assessment of leakage potential for a mature carbon dioxide-enhanced oil recovery project and as a prototype for carbon dioxide sequestration; Rangely field,Colorado

摘要

measurements of CO_2 and CH_4 soil gas concentrations and gas exchange with the atmosphere at a large-scale CO_2-enhanced oil recovery (EOR) operation at Rangely,colorado,United States allowed assessment of the microseepage potential.Shallow and deep soil gas concentrations and direct transport of CO_2 and CH_4,complemented by carbon isotopes, have demonstrate dan estimated microseepage rate to the atmosphere of approximately 400 t CH_4/yr from the 78-km~2 area of the Rangely field.Preliminaryestimates of deep-sourced CO_2 losses are in the range of 170 to less than 3800 t/yr.several holes as much as 9m deep for nested sampling of gas composition,stable carbon isotopic ratios for CO_2 and CH_4,and carbon-14 measurements on CO_2 indicate that deep-sourced CO_2 microseepage loss was detected.Methanotrophic oxidation of microseeping CH_4 ot CO_2 in soils demonstrates significant contribution to soil gas CO_2 in high CH_4 flux areas,necessitting a revision of the estimated direct CO_2 microseepage rate to less than 170 t/yr over the Rangely field.An evaluaton of produced water quality from pre-CO_2-EOR to 1999 demonstrates and increase in some parameters,particularly of Ca~2+ and HCO_3~-,indicating dissolution of ferroan calcite and ferroan dolomite in the Weber Formation.Inverse computer modeling suggested carbonate mineral sequestration was possible within the constraints of evolution of produced water quality.X-ray analyses of well scales,however,do not support the presence of significant mineral sequestration.Instead,modelingindicates that the bulk of the CO_2 that has been injected since 1986 is sequestered as dssolved CO_2.