The Utility of Above-Zone Pressure Measurements in Monitoring Geologically Stored Carbon Dioxide

110 Pages·2009·5.46 MB·English

by  Ethan Richard Chabora

THE UTILITY OF ABOVE-ZONE PRESSURE
MEASUREMENTS IN MONITORING
GEOLOGICALLY STORED CARBON DIOXIDE
A REPORT
SUBMITTED TO THE DEPARTMENT OF ENERGY RESOURCES
ENGINEERING
OF STANFORD UNIVERSITY
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
MASTER OF SCIENCE
By
Ethan Richard Chabora
June 11, 2009
© Copyright by Ethan Richard Chabora 2009
All Rights Reserved
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I certify that I have read this report and that in my
opinion it is fully adequate, in scope and in quality, as
partial fulfillment of the degree of Master of Science in
Petroleum Engineering.
Dr. Sally M. Benson
(Principal advisor)
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Abstract
In response to the alarming rise of atmospheric CO in the last 50 years, a great
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deal of emphasis has been placed on the permanent storage of anthropogenic CO
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emissions in underground geologic formations - a technique known as carbon capture
and storage (CCS). The idea has received much attention since it has the potential to
greatly reduce CO emissions while utilizing known techniques and existing technol-
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ogy developed in other industries. While there are several major injection projects
currently underway, the technique is still in a small-scale, demonstration phase. A
key component to the large-scale implementation of CCS is the ability to monitor
the CO once it has been injected and ensure its long-term retention in the target
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formation.
One of the monitoring methods under investigation and currently employed in
several pilot-scale CCS projects is the continuous measurement of pressure in perme-
able zones immediately overlying the primary storage seal - referred to as ‘above-zone
pressure monitoring.’ The fundamental idea is that pressure perturbations observed
in this ‘monitoring zone’ may indicate leakage out of the intended storage reservoir.
While this idea has been often proposed in the context of natural gas storage, it has
received largely anecdotal mention in the literature and there is little to be found
in the way of published case studies or field data. Several authors have considered
the technique for the purpose of CCS, but their prior evaluations were based on
broad-scale scoping calculations and did not demonstrate the practical use of such
measurements.
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This study extends the current body of work by evaluating the diagnostic capa-
bilities of this technique through numerical simulation of several commonly hypoth-
esized leakage scenarios - including leaky cap rocks, transmissive faults, and leaky
wellbores - and quantitatively comparing the pressure changes measured in the over-
lying zone. The storage reservoir considered in the simulations is a homogeneous and
regionally extensive geologic system comprised of a thick saline aquifer and a thin
monitoring zone of identical geologic composition which are separated by a thick,
low-permeability cap rock. While geologically simplistic, the model is assigned prop-
erties that are representative of currently active storage projects.
Analysis of the pressure changes observed in the monitoring zone during the simu-
lationsrevealsthatdifferentleakagemechanismsproducedistinctpressuresignatures.
Furthermore, the use of a special form of the time derivative of pressure shows clear
behavioral changes when CO is present in the leakage stream. Another key obser-
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vation is that brine displaced by the injected CO may move vertically through the
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caprock and into the monitoring zone. This, in turn, can contribute significantly to
the overall pressure change observed in the monitoring zone while not necessarily in-
dicating leakage of CO . Analytical solutions are also shown to be accurate predictors
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of this brine displacement effect, which may aid in the interpretation of such pressure
signals in practice. Finally, pressure is shown to be a property that is sensitive to
subtle changes in the fluid flow dynamics while being relatively insensitive to the
proximity of the measurement to the source of such changes.
Overall, the above-zone monitoring technique shows potential to be a valuable
tool for detecting and diagnosing CO leakage from a storage reservoir. In addition,
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the collective experience of interpreting pressure transient signals - in the oil and gas
industries, for example - is quite mature, therefore many of the existing techniques
are directly applicable to this new application. Finally, the installation and long-term
operation of subsurface pressure devices is also well established, adding to the overall
appeal and practicality of the technique.
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Acknowledgements
Completion of the this work would not have been possible without the masterful
guidance of my advisor, Dr. Sally M. Benson, whose insight and instincts continually
led to interesting questions and elusive observations. Through our work together, I
have been reminded to appreciate the ‘big picture’ in scientific investigation, which
can often be obscured by the clutter of the minutiae.
Funding for this work was generously provided by the Global Climate and Energy
Project (GCEP), Schlumberger Technology Corporation, and the Department of En-
ergy Resources Engineering at Stanford University. A special acknowledgment goes
to Schlumberger for facilitating my return to graduate school and allowing me the
opportunity to grow as both an employee and an individual.
I would also like to acknowledge my fellow classmates and the faculty in the
Department of Energy Resources Engineering, whose work ethic, perseverance, and
dedication to excellence inspired and motivated me to pursue a new standard in my
own work.
My parents, Robert and Pamela Chabora, are also deserving of my deepest grat-
itude for instilling in me the thirst for intellectual growth, an appreciation for the
academic life, and the confidence to aim higher in life’s undertakings.
Finally, none of this would have been possible without the companionship, dedi-
cation, and constant support of my wife, Stephanie Chabora. No one knows better
than she when I am in need of an encouraging word or a friendly nudge to help me
stay on task and she was always right on cue. For that, I will always be grateful.
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Contents
Abstract v
Acknowledgements vii
Table of Contents viii
List of Tables xi
List of Figures xii
Nomenclature 1
1 Introduction 5
1.1 Climate Change and CCS . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Monitoring, Verification, and Accounting . . . . . . . . . . . . . . . . 6
1.3 Above-Zone Pressure Measurements . . . . . . . . . . . . . . . . . . . 10
1.4 Scope of Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2 Literature Review 13
2.1 Pressure Transient Analysis . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Analysis of Leaky Aquifers . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3 Measurement Sensitivity and Practical Considerations . . . . . . . . . 21
2.4 Above-Zone Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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3 Investigative Approach 27
3.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.2 Formulation of Numerical Approach . . . . . . . . . . . . . . . . . . . 28
3.2.1 Details of the TOUGH2-ECO2N Algorithm . . . . . . . . . . 28
3.2.2 Basic Mesh Architecture . . . . . . . . . . . . . . . . . . . . . 31
3.2.3 Geologic and Fluid Parameters of the System . . . . . . . . . 34
3.3 Comparison to Analytical Solutions . . . . . . . . . . . . . . . . . . . 46
4 Results and Analysis 49
4.1 Diffuse Brine Migration Through Seal . . . . . . . . . . . . . . . . . . 49
4.2 Leakage up a Fault . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3 Leakage up a Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.4 Additional Observations . . . . . . . . . . . . . . . . . . . . . . . . . 76
5 Conclusions and Future Work 81
5.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.2 Remaining Questions for Future Work . . . . . . . . . . . . . . . . . 86
References 87
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