Monitoring Geologic Repositories for CO2

In the debate over the future direction of reducing greenhouse gas (GHG) emissions to the atmosphere, the storage of carbon dioxide (CO₂) in terrestrial and geologic sinks has been identified as a viable means for carbon management.  CO₂ sinks are a natural part of the carbon-cycle in the environment; however, they are not sufficient to absorb all of the CO₂ emitted to the atmosphere each year.  Due to concerns about global climate change related to CO₂ emissions, efforts are underway to better utilize both terrestrial and geologic sinks to offset emissions resulting from fossil fuel combustion and other human activities.  Depleted oil and gas reservoirs, unmineable coalbeds, and deep brine-filled (saline) geologic formations are all being considered as potential storage options.  Over a period of hundreds to thousands of years, some fraction of the CO₂ that has been stored in geologic CO₂ sinks would be expected to leak to the environment (subsurface, near-surface, and atmospheric).  Therefore, to ensure the long-term acceptability of utilizing geologic sinks for CO₂ management to regulatory authorities and the public, a critical area of ongoing research is associated with the development of monitoring, verification, and accounting (MVA) techniques that will be implemented in conjunction with geologic sequestration of CO₂.  An overview of monitoring CO₂ storage projects is provided by the Intergovernmental Panel on Climate Change (IPCC) Special Report on Carbon Dioxide Capture and Storage (www.ipcc.ch/ipccreports/srccs.htm).

 

The United States Department of Energy (USDOE) has been studying MVA techniques that may be implemented in conjunction with CO₂ storage projects, which are summarized in a recently released report titled Monitoring, Verification, and Accounting of CO₂ Stored in Deep Geologic Formations, January 2009 (DOE/NETL-E11/081508).  The USDOE’s Carbon Sequestration Program has been evaluating various carbon capture and sequestration (CCS) technologies since 1997.  On objective of the USDOE is to develop MVA protocols that can identify leakage of CO₂ to the environment in order to ensure 95% and 99% retention of CO₂ by geologic sequestration (GS) by 2008 and 2012, respectively.  As summarized in this USDOE report, the USDOE has been evaluating a broad portfolio of Primary, Secondary, and Potential Additional technologies, applications, and accounting requirements to meet the above noted GS goals.   The overall goal of the USDOE MVA program is to demonstrate that the practice of GS is safe, does not create significant adverse local environmental impacts, and is an effective GHS control technology.  In general, the goals of the MVA research programs are to:

 

·        Improve understanding of storage processes and confirm their effectiveness.

·        Evaluate the interactions of CO₂ with formation solids and fluids.

·       Assess environmental, safety, and health (ES&H) impacts in the event of a leak to the atmosphere.

·        Evaluate and monitor any required remediation efforts should a leak occur.

·        Provide a technical basis to assist in legal disputes resulting from any impact of sequestration technology (groundwater impacts, seismic events, crop losses, etc.).

 

In support of their GS objectives, the USDOE evaluated various monitoring techniques at the following five GS projects taking place in the United States to evaluate and identify the MVA techniques that are most effective and economic for these specific geologic settings: 

·      Gulf Coast Mississippi Strandplain Deep Sandstone, Mississippi.

·      Nugget Sandstone, Wyoming.

·      Cambrian Mt. Simon Sandstone, Ohio.

·      San Joaquin Valley Fluvial-Braided Deep Sandstone, California.

·      Williston Basin Deep Carbonate, North Dakota.

The USDOE identified a broad range of atmospheric, near-surface, and subsurface MVA techniques that could be implemented in conjunction with CO₂ storage projects in geologic sinks, which are described in detail in their report.  Furthermore, the USDOE report also provides an overview of United States Environmental Protection Agency (USEPA) permitting requirements for GS projects.  Finally, the USDOE report describes the results of large-scale tests of MVA techniques performed in the five geologic formations identified above.

 

This article was authored by Greg Tieman, Acacia Environmental Group LLC. For more information on the author see here.