OVERVIEW OF THE ANALOG SITE DATABASE

Figure 5-2 shows the CO2 emission flux values in the analog site database for a total of 28 analog sites that have measurements of deep-sourced CO2 flux values. Twelve of the sites are located in sedimentary basins, and the remaining 16 sites are in VHM settings. Figure 5-2 also shows the typical range of soil respiration rates of CO2 from the ground surface (i.e., 0.05 to 20 µmol/m²-s). The most striking feature of Figure 5-2 is that there is a marked difference between the magnitudes of the CO2 flux values in

sedimentary basins versus those in VHM settings.

0.001 0.01 0.1 1 10 100 1000 10000 100000

Soil respiration Vorderrhon, Germany* Farnham Dome, UT, USA* Springerville-St. Johns, AZ-NM, USA* Rangely CO2 EOR Project, CO, USA Teapot Dome, WY, USA Mesozoic carbonate, Central Italy Otway (Penola), AU Weyburn, CO2 Project, Canada In Salah, CO2 Project, Algeria Otway (Pine Lodge, Permeable Zone), AU Otway (Pine Lodge, Fault), AU Crystal Geyser-Ten Mile Graben (Fault Zone), UT, USA Poas volcano, Costa Rica** Arenal volcano, Costa Rica** Matraderecske, Hungary (Permeable Zone) Dixie Valley Geothermal Field, USA** Oldoinyo Lengai volcano, Tanzania Mammoth Tree Kill Area, CA, USA Albani Hills, Italy Yellowstone volcanic system, USA Solfatara crater, Italy Vulcano Island, Italy** Matraderecske, Hungary (Fault) Miyakejima volcano, Japan** Poggio dell’Ulivo, Italy** Cerro Negro, Nicaragua** Masaya volcano, Nicaragua** Latera, Tuscany, Italy

Area Carbon Dioxide Flux (µmol/m2-s)

Sedimentary Basins Volcanic/Hydrothermal/Metamorphic Settings

* These locations reported flux values of 0 µmol/m²/s

** These locations reported maximum flux values only

Figure 5-2. Plot of CO2 Emission Rate for 28 Analog Sites

CO2 fluxes from both natural and EOR sites in sedimentary basins range as follows:

• Fluxes were measured that are essentially zero at three sites (i.e., Vorderrhon, Germany; Farnham Dome, UT, USA; and Springerville-St. Johns, AZ-NM, USA). Note that in addition, there are several other sedimentary sites (e.g., Jackson Dome, MS and Sleipner, Norway) where it is strongly believed that there are no CO2 emissions from the CO2 reservoirs, but there are no flux monitoring data to support that assumption;

• Fluxes were measured at 0.01 to 1 µmol/m²-s at four sites (i.e., Rangely CO2 EOR Project, CO, USA; Teapot Dome, WY, USA; Mesozoic carbonate, Central Italy; and Otway (Penola), Australia);

• Fluxes were measured at up to 1 to 10 µmol/m²-s at four sites (i.e., Weyburn, CO2 Project, Canada; In Salah, CO2 Project, Algeria; Otway (Pine Lodge, Permeable Zone), Australia; and Otway (Pine Lodge, Fault), Australia); and

• Fluxes were measured at 5 to 170 µmol/m²-s at one site (i.e., Crystal Geyser-Ten Mile Graben (Fault Zone), UT, USA).

Thus, flux rates of CO2 from the sedimentary basin reservoirs are extremely low. At most locations that release CO2, the rates are well below typical soil respiration rates. The only sedimentary basin reservoir where CO2 fluxes significantly exceed typical soil respiration rates is associated with discharge from a fault zone (i.e., Crystal Geyser). Note also that (1) the sedimentary sites with the two highest CO2

emission rates are from measurements associated with fault discharges, and (2) despite the impacts of wells and injection pressure, the fluxes at CO2 injection sites (i.e., Rangely, Weyburn, and In Salah) are still below typical soil respiration rates. These findings for sedimentary basin sites (see Figure 5-2) are consistent with reports in the literature, which note the following:

• There are many CO2 fields in sedimentary basins that have held CO2 for millions of years without any evidence of leakage or environmental impact (IEA Greenhouse Gas R&D Program, 2006a);

• Some CO2 fields in sedimentary basins do leak, but usually via carbonated springs or dry seeps.

This results in either no ecosystem damage or only very localized ecosystem damage (IEA Greenhouse Gas R&D Program, 2006a). Note that since fluxes from most sedimentary basin sites are well below typical soil respiration rates, ecosystem damage would not be expected, since releases from CO2 reservoirs add very little in the way of emissions;

• Natural accumulations occur in a number of different types of sedimentary rocks (principally limestones, dolomites and sandstones), with a variety of seals (i.e., mudstone, shale, salt, and anhydrite), and a range of trap types, reservoir depths, and CO2 -bearing phases (IPCC, 2005);

• Fractures seem to control CO2 migration through the geosphere (IEA Greenhouse Gas R&D Program, 2005);

• CO2 is also emitted from sedimentary basins, many of which occur in tectonically stable regions with little or no VHM activity. In sedimentary basins, CO2 is commonly held in porous

formations such as sandstones/limestones where the super-critical compressed gas is trapped by overlying layers of impermeable rocks, such as marine shales and salt. This is analogous to the way oil and gas is trapped in sedimentary basins. CO2 leaks from sedimentary basins through permeable rocks, faults/fissures in rock, and accidentally via wells. In some cases, springs are observed at faults/wells, but more commonly, CO2 appears at the ground already dispersed to surrounding strata at very low seepage rates (IEA Greenhouse Gas R&D Program, 2006a); and

• Wells that are structurally unsound have the potential to rapidly release large quantities of CO2 to the atmosphere (Lewicki et al., 2006).

CO2 fluxes in VHM settings range as follows:

• Fluxes have been measured above the range of typical soil respiration rates (i.e., 0.05 to 20 µmol/m²-s) at all VHM sites;

• Fluxes were measured from 20 to 200 µmol/m²-s, or roughly one order of magnitude greater than typical soil respiration rates, at seven sites (i.e., Poas volcano, Costa Rica; Arenal volcano, Costa Rica; Matraderecske, Hungary (Permeable Zone); Dixie Valley Geothermal Field, USA;

Oldoinyo Lengai volcano, Tanzania; Mammoth Tree Kill Area, CA, USA; and Albani Hills, Italy); and

• Fluxes were measured up to 2,000 to 20,000 µmol/m²-s, or roughly two to three orders of magnitude greater than typical soil respiration rates, at nine sites (i.e., Yellowstone volcanic system, USA; Solfatara crater, Italy; Vulcano Island, Italy; Matraderecske, Hungary (Fault);

Miyakejima volcano, Japan; Poggio dell’Ulivo, Italy; Cerro Negro, Nicaragua; Masaya volcano, Nicaragua; and Latera, Tuscany, Italy).

Thus, in all of the VHM settings, CO2 is released from the ground at emission rates above typical soil respiration rates. Also, in both VHM settings and sedimentary basins, fault or fracture structures are the primary pathways that result in high CO2 release rates. These findings for VHM settings (see Figure 5-2) are consistent with reports in the literature, which note the following:

• There is a well established correlation between high CO2 emission rates and tectonic zones, seismic activity, and volcanism. As such, most detectable emissions that lead to locally elevated atmospheric CO2 concentrations, and virtually all hazardous leaks, occur in volcanic areas that are highly fractured and, therefore, unsuitable for CO2 sequestration (Benson et al., 2002);

• Fractures seem to control CO2 migration through the geosphere (IEA Greenhouse Gas R&D Program, 2005);

• At some VHM locations in Italy, CO2 emission rates at quite high, with some cases being directly under housing developments. Yet, there is only a very small increase in indoor air CO2

concentrations in some of these areas. However, risks do exist in some areas, as demonstrated by livestock kills, ecosystem damage (IEA Greenhouse Gas R&D Program, 2005), and elevated CO2

concentrations in some VHM settings;

• All of the significant natural CO2 hazards are associated with volcanism and not with any known sedimentary basin CO2 reservoirs, and these hazards are only present in geologic settings that would not be considered for CO2 sequestration (Benson et al., 2002);

• Many natural releases of CO2 have been correlated with a specific event that triggered the release, such as magmatic fluid intrusion or seismic activity (Lewicki et al., 2006). For example, releases due to earthquakes are well documented at Hyogo-ken Nanbu, Japan; Matushiro, Japan; and, Mammoth Mountain CA, USA.

• Unsealed fault and fracture zones may act as fast and direct conduits for CO2 flow from depth to the surface. Determining the potential for and nature of CO2 migration along these structures (Lewicki et al., 2006) is, therefore, important;

• The hazard to human health has been small in most cases of large CO2 surface releases (Lewicki et al., 2006), excluding two events due to lake overturn in Africa; and

• While changes in groundwater chemistry were related to CO2 leakage due to acidification and interaction with host rocks along flow paths, waters remained potable in most cases (Lewicki et al., 2006).