GCCC
 
Expert-Based Development of a Site-Specific Standard in CO2 Sequestration Monitoring Technology
Process for Quantitative Assessment of Tool Site-Specific Effectiveness Back to Overview          

A number of variables determine whether a tool is effective. In this study, we focus on those variables that are site specific. However, to make a clear evaluation, we have prepared a list of factors that influence whether a tool is effective, so that those that are not site specific can be dealt with via specifying best available technologies.
Many variables interact to determine whether a tool is effective, adding complexity to our assessment. In this study we force a rather artificial single-variable approach on the assessment. In addition, we have initially selected sets of variables that we think will have a strong effect on tool sensitivity, which is subject to revision as the assessment matures.

One major difficulty in determining the appropriateness of tools is determining the appropriate signal threshold that it is desirable to detect. EPA rules provide no threshold below which a leakage or mismatch with model results are considered negligible.

The table below provides, for each tool type, a preliminary list of site-specific and non-site-specific variables that impact tool sensitivity. In the next year this matrix will be assessed more deeply via literature review, expert panel review, and where needed in a numerical modeling of tool sensitivity. This version of the table is assembled for the purpose of discussion.

Preliminary inventory of site-specific factors that influence tool sensitivity compared with general factors that are the same at all sites.

Compartment tested

Non-site-specific factors that influence tool sensitivity*

Site-specific factors that influence tool sensitivity*

Notes

CO2 concentration of air

Analytical detection limits
Sample height
Location of sample point with respect to leakage path

Ambient daily and seasonal variation
Across-site variation in ambient CO2 emissions
Dilution between emission point and sample point

 

Natural or introduced CO2 tracers sampled in air

Analytical detection limits
Lab/sampler contamination
Location of sample point with respect to leakage path

Difference between ambient composition and injectate composition
Stability of tracer during leakage process, dissolution, sorption processes

Even introduced tracers have some background in environment

Percent CO2 in soil gas (relative to O2 and N2)

Analytical detection limits
Well construction—atmospheric contamination

Ratio of leakage rate to natural cycling processes
In situ CO2 production, release, dissolution, sorption processes

Collecting O2 and N2 provides process information

Natural CO2 tracers (δC13, noble gasses) sampled in soil gas

Analytical detection limits
Lab/sampler contamination
Location of sample point with respect to leakage path

Difference between ambient composition and injectate composition
Stability of tracer during leakage process

These tracers may be more conservative and therefore more sensitive than CO2 itself.

Introduced CO2 tracers (PFT) sampled in soil gas

Analytical detection limits
Lab/sampler contamination
Location of sample point with respect to leakage path

Stability of tracer during leakage process, e.g., dissolution, sorption during transport

Even introduced tracers have some background in environment

Groundwater salinity

Well-completion issues, perforated interval, mixing along sand pack,
Analytical detection limits
Location of well sample point with respect to leakage path, considering density, mixing

Ambient variably in salinity
Aquifer flow rate and process, mixing

Might use near-surface conductivity to sample a larger area

Groundwater/above-zone monitoring interval (AZMI) pH

Analytical detection limits
Sampling process, outgassing
Location of well sample point with respect to leakage path, considering density, mixing

pH change with respect to introduced CO2, buffering
Ambient variably in pH
Aquifer flow rate and process, mixing

pH is sensitive to sampling procedure, especially temperature, pressure, and outgassing

Groundwater/AZMI DOC/DIC

Analytical detection limits
Location of well sample point with respect to leakage path, considering density, mixing

Ambient variably in DOC/DIC
Aquifer flow rate and process, mixing
Sorption and mineral reaction

Best used in combination with other measurements

Groundwater/AZMI Head-space gas

Analytical detection limits
Location of well sample point with respect to leakage path, considering density, mixing

Ambient variably in free/dissolved CO2
Aquifer flow rate and process, mixing
Sorption and mineral reaction

Head gas is sensitive to temperature, outgassing, sampling procedure
Best used in combination with other measurements

Groundwater/AZMI major and minor elements

Analytical detection limits
Location of well sample point with respect to leakage path, considering density, mixing

Ambient variably in major and minor elements
Aquifer flow rate and process, mixing
Sorption and mineral reaction

Sensitive to lab detection limits, proper sampling, stabilization and curation for various elements and compounds; best used in combination with other measurements constituents

Confined aquifer/ AZMI pressure

Gage sensitivity, depth error in positioning gage, land surface elevation error.
Well completion, perforations, well fluids
Location of well measurement point with respect to leakage path

Aquifer ambient variability to recharge, barometric pressure, tides, etc., fluid density; monitored zone thickness, transmissivity, storativity

 

Pressure in injection zone

Gage sensitivity, depth error in positioning gage
Well completion, perforations, well fluids

Ambient variability to recharge, barometric pressure, tides, etc., fluid density; zone thickness, transitivity, storativity

 

Tubing pressure at wellhead

Noise from daily thermal variations
Well completion, perforations, well fluids

Rate of breakthrough.
Dissolved CO2 may complicate response
Non-CO2 fluid changes will complicate response

 

Pulsed neutron logging to detect CO2 saturation in injection zone or in AZMI

Well completion, perforations, well fluids
Tool construction and deployment
Processing of sigma
Near-well-bore perturbations

Salinity of ambient fluids
Saturation of CO2
Noise
Stratigraphic complexity, bed thickness

Complex processing is possible

Resistivity logging to detect CO2 saturation in injection zone or in AZMI

Well completion, perforations, well fluids
Tool construction and deployment
Processing
Near-well-bore perturbations

Salinity of ambient fluids.
Saturation of CO2
Noise
Stratigraphic complexity, bed thickness

Not used in steel wells

Sonic logging to detect CO2 saturation in injection zone or AZMI

Well completion, perforations, well fluids
Tool construction and deployment
Processing of signal
Near-well-bore perturbations

Change in impedance and velocity with change in CO2 saturation
Stratigraphic complexity, bed thickness
Saturation of CO2
Noise

Tool size can limit deployment

2-D seismic profiling to locate plume edge

Source selection, receiver deployment, many variations in set-up
Processing

Static error
Signal:noise ratio
Change in impedance and velocity with change in CO2 saturation
Stratigraphic complexity, bed thickness, depth
Saturation of CO2

Multiple variables intersect complexly
Focus area for CCP study

Walk-away VSP to locate plume edge

Source selection, receiver deployment, many variations in set-up
Processing

Static error
Signal: noise ratio
Change in impedance and velocity with change in CO2 saturation
Stratigraphic complexity, bed thickness
Saturation of CO2

Multiple variables intersect complexly
Higher vertical resolution; limited horizontal coverage
Focus area for CCP study

3-D seismic survey for locate plume edge

Source selection, receiver deployment, many variations in set-up
Processing

Static error
Signal: noise ratio
Change in impedance and velocity with change in CO2 saturation.
Stratigraphic complexity, bed thickness, depth
Saturation of CO2

Multiple variables intersect complexly
Focus area for CCP study

Surface gravity

Consideration deferred

 

Focus area for CCP study

Surface electrical and magnetic techniques

Consideration deferred

 

Focus area for CCP study

* Sensitivity is quantifiable response to the specified signal

 

 
 

 




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The GCCC seeks to apply its technical and educational resources to implement geologic storage of anthropogenic carbon dioxide on an aggressive time scale with a focus in a region where large-scale reduction of atmospheric releases is needed and short term action is possible.

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