Negative Emissions Technologies and Reliable Sequestration A Research Agenda (2019) / Chapter Skim
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7 Sequestration of Supercritical CO2 in Deep Sedimentary Geological Formations
7 Sequestration of Supercritical CO2 in Deep Sedimentary Geological Formations
Pages 319-350
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From page 319... ...
Because the supercritical CO2 is less dense than the fluids that initially fill the pore spaces in the rocks, it will rise by buoyancy forces through the reservoir rocks until it encounters a low permeability rock, typically called a reservoir seal. Seals are composed of shale, anhydrite, or low permeability carbonate rocks.
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From page 320... ...
Several comprehensive reviews and research roadmaps lay out the scientific and engineering basis for secure sequestration; discuss site characterization and selection; describe effective monitoring and risk assessment and management approaches; and estimate global sequestration capacity and costs (Bachu, 2015; de Coninck and Benson, 2014; DOE, 2017d, g; Rubin et al., 2015; U.S. Geological Survey, 2013)
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From page 321... ...
Beyond this are site-specific requirements regarding the absence of permeable faults and fractures penetrating the seal, a known and ideally low number of existing wells that could provide leakage pathways, favorable geomechanical conditions to avoid fracturing the reservoir or seal during injection, suitable conditions for monitoring, low likelihood of affecting groundwater, and compatibility with existing land and resource use. Sequestration security may also be enhanced by secondary trapping mechanisms that act over time to reduce the risk of leakage of CO2 out of the storage reservoir.
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From page 322... ...
. Modeling and Simulation Robust numerical modeling of CO2 plume migration, pressure buildup, geomechanical effects, and geochemical reactions are required for the design, optimization, and performance confirmation of sequestration projects.
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From page 323... ...
Volume-averaged properties typically rely on empirical parameterizations that are obtained from laboratory experiments conducted on small samples over short periods of time under conditions which may or may not be representative of actual conditions during the sequestration project. For example, relative permeability is used to parameterize how multiple fluids phases (e.g., CO2 and water)
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From page 324... ...
. Stochastic simulations are used to obtain probabilistic estimates K of plume migration, trapping fractions, and sequestration capacity.
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From page 325... ...
. Pressure data from the monitoring wells can be used to assess the extent to which the pressure buildup extends throughout the storage reservoir, which is important for understanding the "area of review"1 and for predicting how multiple sequestration projects in the same reservoir might interact.
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From page 326... ...
Seismic events induced by pressure increases due to CO2 injection need to be monitored to provide assurance that they do not present a hazard to structures, people, or the integrity of the reservoir seal. Table 7.1 summarizes information about microseismic events associated with geological sequestration and EOR projects.
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From page 327... ...
Field experiments have employed several approaches for monitoring CO2 directly, or indirectly in TABLE 7.1 Microseismic Events Measured at Sites with CO2 Injection for Sequestration or EOR (from)
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From page 328... ...
It has also provided a wealth of experience and data to advance our understanding about migration of CO2 in the subsurface and the use of seismic imaging to track migration of the plume. Including the Sleipner Project, there have been five commercial-scale sequestration projects in saline aquifers (Table 7.3)
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From page 329... ...
Site characterization, Geological, hydrogeological, geomechanical, and geochemical site selection, and risk characterization. Assessment of sequestration capacity, sealing potential, and assessment.
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From page 330... ...
The Gorgon Project in Northwest Australia will be the largest saline aquifer sequestration project and is expected to sequester from 3-4 Mt/y and to begin operations shortly (Flett et al., 2009)
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From page 331... ...
. The extent to which pressure buildup limits sequestration capacity is captured by the concept of a dynamic capacity that is constrained by the maximum rate of injection that will avoid excessive pressure buildup in a geological formation.
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From page 332... ...
The footprint per ton of CO2 for a sequestration project is highly site specific, depending on the architecture of the storage formation and seal, petrophysical properties of the rocks, pressure and temperature of the storage formation, and extent of secondary trapping. For example, footprint estimates for Sleipner are about 1-3 t/m2 (Furre et al., 2017)
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From page 333... ...
The wide range reflects the highly site-specific nature of geologic sequestration projects. Primary variables include the depth of the formation, number of injection wells required, existing land uses, and ease of deploying monitoring programs.
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From page 334... ...
International guidelines for tracking and reporting greenhouse gas emissions have been developed for inventory accounting of CO2 capture and sequestration projects (IPCC, 2006)
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From page 335... ...
Although the risks of leakage or other environmental harm are expected to decrease over time because of the secondary trapping mechanisms and pressure decreases in the post-project period, the possibility nevertheless remains that some CO2 could leak out of the reservoir. After the project has been shut down, who is responsible for monitoring and remediation, for how long, and with what mechanism?
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From page 336... ...
To put this into perspective, 5-10 Gt/y sequestration in deep geological formations would require more than a 100-fold scale-up from current sequestration operations and would assume the scale of global oil production, which is a $2 trillion/y industry. The enormous sequestration capacity of geological formations combined with the permanent nature of geological storage warrant a significant investment in research and development (R&D)
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From page 337... ...
This massive scale-up in geological sequestration will require more intense resource utilization and development of new sequestration resources that may rely on advanced reservoir engineering practices that remain in their infancy, such as accelerated secondary trapping mechanisms and reservoir pressure management. These activities will support net emissions as well as sequestration from fossil fuel sources.
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From page 338... ...
The potential for harmful earthquakes and the extent to which cautionary exclusion of some locations will affect estimates of sequestration capacity need to be evaluated. Specific research directions include the following: • Understanding why some CO2 sequestration sites experience induced earth quakes and other do not; • Determining the potential for pre-qualifying sites to avoid induced events us ing the best available models and data; • Developing short-term tests to assess the risks of induced earthquakes before committing to a project; • Understanding the implications of induced seismicity on sequestration capac ity estimates and injectivity rates; • Developing mitigation approaches for minimizing risks, such as brine extrac tion, injection pressure management, or requiring both a top and bottom seal; and • Understanding the potential for fault slip to increase leakage from the seques tration reservoir.
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From page 339... ...
This research would improve understanding of and reduce the risks of induced seismicity at geological sequestration sites, develop methods for assessing and mitigat ing risks of seismicity, improve capacity estimates by screening sites that are high risk for induced seismicity, and help quantify the risk of leakage from fault slippage. Improving second- 25 10 This research program would support a 10-y multi-investigator team to perform a ary trapping predic- large-scale experiment designed to quantify the effectiveness of natural and acceler tion and methods to ated trapping for immobilizing CO2 in the post-injection period.
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From page 340... ...
This program would develop the knowledge needed to develop and demonstrate the following: efficient and effective methods for characterizing geological sequestration sites over the large footprint of a commercial-scale CO2 sequestration project (~100 km2) , methods for identifying and characterizing faults in seals and basement rocks; and meth ods of characterizing geological heterogeneity and associated trapping of CO2.
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From page 341... ...
Provide educational materials for increasing awareness of the need, opportu Deployment public engagement nity, risks, and benefits of geological sequestration for negative emissions. effectiveness with local communities and the general public 341
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From page 342... ...
Site characterization and selection is arguably the single-most important factor for secure and reliable CO2 sequestration in sedimentary rocks, but it poses challenges beyond what is required for oil and gas exploration and production. Research needs associated with the scale-up of commercial sequestration projects include the following: • Developing and demonstrating efficient and effective methods for character izing the reservoir and seal.
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From page 343... ...
This information can calibrate and validate the simulation models that are used for a variety of purposes, including resource optimization, forecasts of plume migration during the post-injection period, and regulatory compliance. • Strategies and technologies are needed for an adaptive monitoring program that is site-specific and responsive to the changing needs and conditions of the sequestration projects.
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From page 344... ...
The benefits of secondary trapping mechanisms, such as solubility trapping, residual gas trapping, and mineral trapping, compensate for flaws in either the seal or in the leakage pathways created by wells penetrating the seal above the sequestration reservoir (see "Geological Requirements for Secure and Reliable Sequestration" above)
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From page 345... ...
For such projects to become carbon negative, they must significantly increase the ratio of CO2 injected per barrel of oil recovered. Research is needed to develop reservoir engineering methods to cooptimize CO2 sequestration and enhanced oil recovery because current approaches for CO2-EOR are not likely to efficiently sequester more CO2 simply by increasing the amount of CO2 injection.
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From page 346... ...
Simulating the multiscale, multiphysics, coupled processes that influence the fate and transport of supercritical CO2 injected into sedimentary rocks remains a grand challenge that underpins critical aspects of geological sequestration of CO2. Site selection, storage engineering, risk assessment, and project performance confirmation all rely heavily on the veracity of simulation models.
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From page 347... ...
This budget reflects a substantial increase of the DOE 2017 budget for CO2 sequestration in deep geological formations (DOE, 2018) , as well as the additional and unique needs associated with sequestration for the purposes of negative emissions.
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From page 348... ...
TABLE 7.6 U.S. Federal Agency Responsibilities for the Research Needs and Data Repository Research Need DOE NSF EPA DOI Induced seismicity X X X Characterization X X X and site selection Monitoring X Accelerated X trapping Co-optimization of X EOR/sequestration Environmental impacts and risk X X assessment Model X X development Data repository X 348
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From page 349... ...
However, there is an enormous difference between megaton-scale EOR projects in oil fields and sequestration of billions of tons of CO2 per year in deep saline aquifers. Implementing the research agenda outlined above will yield information essential for storing enough CO2 to make a substantial contribution to greenhouse gas mitigation.
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