EOR as Sequestration: Geoscience Perspective

Dr. Susan D. Hovorka and Dr. Scott Tinker

 

Gulf Coast Carbon Center
Bureau of Economic Geology
Jackson School of Geosciences
The University of Texas at Austin
Austin, TX 78712
e-mail

 

CO2 Enhanced Oil Recovery (EOR) has a development and operational history several decades longer than geologic sequestration of CO2 designed to benefit the atmosphere and provides much of the experience on which confidence in the newer technology is based. With modest increases in surveillance and accounting, future CO2 EOR using anthropogenic CO2 (CO2-A) captured to decrease atmospheric emissions can be used as part of a sequestration program.


Confidence in permanence of sequestration of CO2 placed as part an EOR program will be in some cases higher than CO2 placed into an equivalent brine-bearing system, and in some cases lower. Confidence is increased for the EOR case because: 


• the quality of the confining system is better documented, 

• pressure and fluid flow are controlled by production, 

• more CO2 is dissolved 

• the reservoir properties are better known because of reservoir characterization and fluid
production history leading to more robust prediction of the long term fate of CO2.
Leakage risk factors that are increased for CO2 injected as part of an EOR program and must be
assessed both through research and field-specific mitigation are:

• CO2 that migrates out of pattern may be produced from non project wells and not
recycled

• Numerous well penetrations of the confining system create potential flaws that, if
unmitigated could allow CO2 to leak slowly over long time periods at rates unacceptable
to attaining atmospheric goals.
 

Non-geotechnical factors that favor the use of CO2 EOR for sequestration may be more important than technical factors. These include:

• Economical and societal benefits

• Mature regulatory and legal environment

• Public acceptance
 

Use of CO2 EOR to accelerate sequestration will be most effective if it builds upon well established current best practices by increasing accounting and monitoring requirements based on surveillance already conducted for successful operation of a flood. To document that CO2 is retained in the subsurface will require reporting some data to stakeholders that operators have traditionally used only in-company. In addition collection of some new data will be needed to document permanence of sequestration, focusing on the areas of leakage risk. Additional studies  focused on CO as EOR are proposed to document how to best collect this data. 
 

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