Is It Possible to Detect Gas Seepage from CO2-EOR Projects?
Experience at Rangely,
Carbon dioxide sequestration in spent oil and gas fields as
part of a CO2-EOR program will likely be an early option that has economic
advantages. A concern is the potential for gas microseepage
under the overpressured conditions necessary for
operation, particularly for CH4. A comparison was made between the overpressured Rangely, Colorado
CO2-EOR operation and the underpressured Teapot Dome
oil field in
Fluxes of CO2 and CH4 into the atmosphere under winter conditions of low
soil biological activity were determined at both the Rangely
and
Ten-meter deep holes were augured for nested soil gas sampling at selected locations of interest for more thorough characterization, including areas of gas microseepage and background. In anomalous locations, a substantial proportion of deep-sourced CH4 was bacterially oxidized in the unsaturated zone, producing isotopically distinctive, and radiocarbon-depleted CO2. Carbon isotopic composition of surface materials, such as calcite veins, caliche, vegetation, soil organic and inorganic matter are essential in the characterization of processes operating in the near-surface, that reflect seepage.