The Utility of Above-Zone Pressure Measurements in Monitoring Geologically Stored Carbon Dioxide
Abstract/Contents
- Abstract
- In response to the alarming rise of atmospheric CO2 in the last 50 years, a great deal of emphasis has been placed on the permanent storage of anthropogenic CO2 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 CO2 emissions while utilizing known techniques and existing technology 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 CO2 once it has been injected and ensure its long-term retention in the target formation. One of the monitoring methods under investigation and currently employed in several pilot-scale CCS projects is the continuous measurement of pressure in permeable 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 eld 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. This study extends the current body of work by evaluating the diagnostic capabilities of this technique through numerical simulation of several commonly hypothesized leakage scenarios - including leaky cap rocks, transmissive faults, and leaky wellbores - and quantitatively comparing the pressure changes measured in the overlying 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 properties that are representative of currently active storage projects. Analysis of the pressure changes observed in the monitoring zone during the simulations reveals that different leakage mechanisms produce distinct pressure signatures. Furthermore, the use of a special form of the time derivative of pressure shows clear behavioral changes when CO2 is present in the leakage stream. Another key observation is that brine displaced by the injected CO2 may move vertically through the 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 indicating leakage of CO2. Analytical solutions are also shown to be accurate predictors 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 ow 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 CO2 leakage from a storage reservoir. In addition, 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.
Description
| Type of resource | text |
|---|---|
| Date created | June 2009 |
Creators/Contributors
| Author | Chabora, Ethan Richard |
|---|---|
| Primary advisor | Benson, Sally M. |
| Degree granting institution | Stanford University, Department of Energy Resources Engineering |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Genre | Thesis |
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Preferred citation
- Preferred Citation
- Chabora, Ethan Richard. (2009). The Utility of Above-Zone Pressure Measurements in Monitoring Geologically Stored Carbon Dioxide. Stanford Digital Repository. Available at: https://purl.stanford.edu/nt627yd2014
Collection
Master's Theses, Doerr School of Sustainability
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