Assessing the Effectiveness of Pressure Monitoring for Detection of Brine and CO2 Leakage
Abstract
The US DOE National Risk Assessment Partnership (NRAP), funded through the Office of Fossil Energy and the National Energy Technology Laboratory is developing methods to evaluate the effectiveness of monitoring techniques to detect brine and CO2 leakage up legacy wells into underground sources of drinking water (USDW) overlying a CO2 storage reservoir. As part of the NRAP Strategic Monitoring task group, we developed a model of a sequence of aquifers overlying a hypothetical CO2 storage reservoir in the Vedder Fm., near Kimberlina in the southern San Joaquin Basin, California. The pressure and CO2 plumes in the storage reservoir that reach the bottom of a legacy well located 1 km from the CO2 injection well can cause brine and CO2 to leak up the legacy well, which drive changes in pressure, CO2 saturation and total dissolved solids (TDS) in the overlying aquifers. Supercritical CO2 which migrates to depths less than 700 m undergoes a phase change to gaseous CO2, which can cause a large rise in pressure because gaseous CO2 is much less dense than supercritical CO2. Depending on the timing of phase change, it can continue to drive overpressure after the leakage flux has peaked. Surface-based geophysical monitoring methods, such as electrical resistance tomography, magnetotellurics, and gravity, become more effective with increasing volume of the CO2 and TDS plumes, which increase with cumulative leakage mass and aquifer permeability. The effectiveness of pressure monitoring depends strongly on leakage rate, in addition to cumulative leakage mass, and decreases with aquifer permeability (due to larger permeability dissipating pressure buildup more readily), which is the opposite of surface-based geophysical methods. This results in pressure monitoring being a complementary tool to surface-based geophysical methods. Because of its strong dependence on leakage rate, rather than just cumulative leakage mass, pressure monitoring may be a useful for early leak detection. In contrast to surface-based geophysical methods, a challenge for pressure monitoring is that it requires base-lining the original pressure conditions, requiring early deployment an array of pressure-monitoring wells.
This work was performed under the auspices of the US DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S51F0399B
- Keywords:
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- 0520 Data analysis: algorithms and implementation;
- COMPUTATIONAL GEOPHYSICSDE: 0599 General or miscellaneous;
- COMPUTATIONAL GEOPHYSICSDE: 7290 Computational seismology;
- SEISMOLOGYDE: 7299 General or miscellaneous;
- SEISMOLOGY