275300 Reactive Transport Modeling and Scanning Electron Microscope Analyses to Evaluate Interactions Between Pozzolan-Amended Wellbore Cement and Acid Gas (CO2 + H2S) Under Typical Acid Gas Sequestration Conditions

Monday, October 29, 2012: 4:30 PM
304 (Convention Center )
Liwei Zhang1, David Dzombak1, David Nakles1, Steve Hawthorne2, Barbara Kutchko3, Christina Lopano3, Brian Strazisar3, Li Li4 and Leopold Brunet4, (1)Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA, (2)Energy and Environmental Research Center, University of North Dakota , Grand Forks, ND, (3)National Energy Technology Laboratory, Pittsburgh, PA, (4)Department of Energy and Mineral Engineering, Pennsylvania State University, University Park, PA


Capture and subsurface co-sequestration of acid gas (H2S and CO2) is one sequestration approach that can reduce the emission of both CO­2 and H2S from combustion of fossil fuel. Before the implementation of acid gas co-sequestration, the potential of acid gas leakage along existing and abandoned wellbores at potential sequestration sites needs to be evaluated. Reactive transport modeling is a powerful tool to simulate the interactions between wellbore cement and CO­2 + H2S, so as to evaluate the potential of acid gas leakage along existing and abandoned wellbores. In this study, the interactions between pozzolan-amended wellbore cement and acid gas were simulated with the reactive transport modeling program CrunchFlow.  Key outputs from simulation include calcite weight percentage, pH, porosity, and pyrite and ettringite weight percentages from the exterior to the interior of the pozzolan-amended wellbore cement. SEM-BSE and SEM-EDS analyses on pozzolan-amended cement samples exposed to CO­2 and H2S were conducted, and results were used to calibrate the CrunchFlow simulation model. The model simulation results are consistent with SEM-BSE and SEM-EDS analyses results from the experimental samples. Both model simulation and experimental results show that at the experimental exposure conditions (T = 50 oC, P = 151 bar, 21 mole % H2S : 79 mole % CO2, samples immersed in 1 wt% NaCl solution), the alteration of pozzolan-amended wellbore cement is not significant. However, model simulation reveals that an increase of CO2 partial pressure or H2S partial pressure by 50% can both lead to significant alteration of the properties of wellbore cement and perhaps increase the risk of acid gas leakage.  Results of the wellbore cement exposure experiments and the related reactive transport modeling are being employed to guide development of a reactive transport model for acid gas migration along an entire wellbore.

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See more of this Session: Complex Subsurface Processes
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