University of Texas at Austin

Expert-Based Development of a Site-Specific Standard in CO2 Sequestration Monitoring Technology

  • Program Overview
  • Task 1
  • Task 2
  • Task 3
How to Monitor

Program Overview

The purpose of this project is to provide information needed by project developers as they work with the Environmental Protection Agency (EPA) and state Underground Injection Control Program (UIC) Directors to determine the most appropriate monitoring, reporting, and verification (MRV) approaches and strategies for a CO2 injection site. Two regulations (Environmental Protection Agency, 2010a [Part RR and UU], 2010b [UIC]) require monitoring of greenhouse gases, including those injected into the subsurface, as part of an MRV plan. This project will provide a technical basis to support decision making on how this required monitoring should be accomplished. Relevant guidance documents are in development by the EPA.

It is widely believed that a monitoring strategy should be tailored to the sequestration site and the main tool that ensures that CO2 is retained in a zone is extensive site characterization. In recently released rules, the EPA Regional Administrator or his/her delegates are given authority to develop an MRV plan that is optimized for site-specific characteristics. Within the scope of these rules, this study is designed to fill a gap in guidance to determine how to match the site with the possible technologies.

The specific objectives of the research are to

  • Quantitatively evaluate potential monitoring strategies to select an array of strategies and guidelines for application to specific sites,
  • Test the results of evaluation against the growing array of field measurements gathered from past and current test sites in the U.S. and around the world,
  • Develop widespread consensus that these strategies are adequate when properly applied, and
  • Compile a test/teaching set of cases for testing strategies and then train practitioners in applying the strategies to an array of sites.

Work has begun on the following tasks. Click the tabbed links at the top of this page for more information:

  1. Developing contacts and input from experts in the field
  2. Selecting tools to be studied
  3. Developing a process for quantitative assessment of tool site-specific effectiveness

The study is led by Susan Hovorka and JP Nicot at the Gulf Coast Carbon Center (GCCC). It is funded by the EPA and is supplemented by a parallel activities funded by the Carbon Capture Project (CCP).

Developing contacts and input from experts in the field

Expert Panel

Susan Hovorka (left) and JP Nicot (far right corner) along with other members of the Expert Panel at the kick-off meeting in Natchez, MS.

The study undertakes to provide technical background information to support regulators and project developers in matching selected monitoring tools and protocols with sites and uncertainties at those sites. Because this arena is rapidly evolving and developing, we have expended significant effort drawing information from diverse sources. Regulators, industries with potential CO2 supply, policy developers, and the public provide input in the areas of concern that should be considered in developing a monitoring program. Tool developers and data reduction specialists provide technical expertise. Monitoring experts with field experience provide information on performance in terms of durability and sensitivity of tools under actual field conditions.

GCCC team, members have attended more than 50 workshops, seminars, and public and closed meetings during 2010. We have inventoried global progress on performance of monitoring tools, as well as available information on best approaches.

In the first year of the project we contacted experts to provide input into study design and provide field experience with monitoring tools. Collaboration with Carbon Capture Project (CCP) provides additional expert advice especially outside of the US and in the several sub-disciplines of geophysics.

We also selected a panel of fifteen experts to serve as advisors to this project. The initial expert panel meeting was held in Natchez, Mississippi on May 5, 2010, in conjunction with the IEA Greenhouse Gas R&D Programme monitoring network meeting.

Selecting tools to be studied

Selection of monitoring tools is a complex process that involves a number of factors, the site-specific characteristics of which influence only a few. The process of testing and monitoring (T&M) and monitoring, reporting, and verification (MRV) are still immature, with both active discussion of policy and regulatory needs and assessment via field tests and tool development.

Monitoring in the context of GS has been previously explored and considered, with a number of summaries of approaches, e.g., Nicot and Hovorka (2008), Benson and Cook (2005), GEO-SEQ (2004), DOE NETL Monitoring Best Practices, and WRI Best Practices, among others. Although these documents highlight and rank some of the benefits of various tool types, none of them provides rigorous guidance on the limits of tool sensitivity needed to select a site-specific monitoring procedure. In addition, no consistent view on how to monitor has wide acceptance among technical practitioners, leaving us uncertain as to how to deploy an adequate monitoring program.

Considering uncertainty in the variables that will drive monitoring tools selection, we considered three characteristics in selecting the first tools for assessment.

  • Availability of a reasonable body of relevant experience from which the site-specific sensitivity of a tool can be assessed: We considered tools that had been tested in a list of past GS pilots that we considered "monitoring dense" and for which experts are available to consult.
  • Interest in using a tool for monitoring in diverse sites: We considered suites of similar projects that we are working on, and attempted to imagine site types with a range of properties. For example, we imagined structural closures and regionally extensive dipping (with respect to buoyant trapping of free-phase CO2); hydrologically closed and hydrologically open boundary conditions (with respect to brine displacement and pressure build-up, stratigraphically simple, thick, uniform injection zones and highly heterogeneous injection zones); thick and thin injection zones; well-characterized seals and uncertain seals; injection at shallow (>2,000 ft) to deep (>10,000 ft); different surface conditions such as offshore, mountainous, wetland, urban, cropped, thickly forested, and different types of above-injection-zone geology. Next year, models construction will more formally assess this diversity.
  • Tools shown to be useful, sensitive to measuring needed parameters, and durable in the field: We did not select tools thought to be of questionable value. In addition, commercial tools that can be purchased from service companies or vendors were preferentially selected for the first assessments. This choice should not be interpreted to imply that new methods now in development will rise to the front; in fact we hope that this is true.

We anticipate that during the course of this project and during the years following project completion, the list of tools selected will grow. However, for this first year and for the methods development proposal to be submitted to the expert panelists early next year, we proscribed the initial tools selected very narrowly so as to assist in methodology development. The following list summarizes our initial tool selection.

  • Direct sampling of CO2 concentration of air
  • Direct sampling of natural or introduced CO2 tracers sampled in air
  • Direct sampling of percent CO2 in soil gas (relative to O and N2)
  • Direct sampling of natural CO2 tracers (δC13, noble gasses) sampled in soil gas
  • Direct sampling of introduced CO2 tracers (PFT) sampled in soil gas
  • Direct sampling of groundwater/above-zone monitoring interval pH
  • Direct sampling of groundwater/above-zone monitoring interval DOC/DIC
  • Direct sampling of groundwater/above-zone monitoring interval head-space gas
  • Direct sampling of groundwater/above-zone monitoring interval major and minor elements
  • Confined aquifer above-zone monitoring interval pressure using a pressure transducer below water table with hourly readouts
  • Pressure in injection zone using bottom-hole pressure and temperature gage in perforated well bore, isolated with packer with hourly readouts
  • Surface pressure-based measurement of CO2 breakthrough using tubing pressure at wellhead
  • Pulsed neutron logging to detect CO2 saturation in injection zone or above-zone monitoring interval using commercial wireline deployment and data interpretation
  • Resistivity logging to detect CO2 satuaration in injection zone or above-zone monitoring interval using commercial wireline deployment and data interpretation
  • Sonic logging to detect CO2 saturation in injection zone or above-zone monitoring interval using commercial wireline deployment and data interpretation
  • 2-D seismic profiling to locate free-phase CO2 assuming standard commercial deployment and processing with best practices
  • Offset or walk-away VSP to locate free-phase CO2 plume edge assuming standard commercial deployment and processing with best practices
  • 3-D seismic profiling to locate free-phase CO2 assuming standard commercial deployment and processing with best practices

Additionally, the following tools mentioned by UIC class VI as examples represent future tool development. As these are novel techniques, consideration of these tools is currently deferred.

  • Gravity survey to locate free-phase CO2 plume edge
  • Electrical and magnetic techniques survey to locate free-phase CO2 plume edge

Developing a process for quantitative assessment of tool site-specific effectiveness

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

FAQs

co2 facts
STORE

For a flyer on GCCC mission, activities, impact, and goals, please click here.