Wellbore integrity analysis of a natural CO2 producer

Abstract
Long-term integrity of existing wells in a CO2-rich environment is essential for ensuring that geological sequestration of CO2 will be an effective technology for mitigating greenhouse gas-induced climate change. The potential for wellbore leakage depends in part on the quality of the original construction as well as geochemical and geomechanical stresses that occur over its life-cycle. Field data are essential for assessing the integrated effect of these factors and their impact on wellbore integrity, defined as the maintenance of isolation between subsurface intervals. In this report, we investigate a 30-year-old well from a natural CO2 production reservoir using a suite of downhole and laboratory tests to characterize isolation performance. These tests included mineralogical and hydrological characterization of 10 core samples of casing/cement/formation, wireline surveys to evaluate well conditions, fluid samples and an in situ permeability test. We find evidence for CO2 migration in the occurrence of carbonated cement and calculate that the effective permeability of an 11′-region of the wellbore barrier system was between 0.5 and 1 milliDarcy. Despite these observations, we find that the amount of fluid migration along the wellbore was probably small because of several factors: the amount of carbonation decreased with distance from the reservoir, cement permeability was low (0.3-30 microDarcy), the cement-casing and cement-formation interfaces were tight, the casing was not corroded, fluid samples lacked CO2, and the pressure gradient between reservoir and caprock was maintained. We conclude that the barrier system has ultimately performed well over the last 3 decades. These results will be used as part of a broader effort to develop a long-term predictive simulation tool to assess wellbore integrity performance in CO2 storage sites. © 2009 Elsevier Ltd. All rights reserved.

Citation
Crow W, Carey JW, Gasda S, Brian Williams D, Celia M (2010) Wellbore integrity analysis of a natural CO2 producer. International Journal of Greenhouse Gas Control 4: 186–197. Available: http://dx.doi.org/10.1016/j.ijggc.2009.10.010.

Acknowledgements
The authors express their appreciation to the management of Carbon Capture Project Phase 2 member companies for support of this project. CCP2 member companies are: BP Alternative Energy, Chevron, ConocoPhillips, Eni, StatoilHydro, Petrobras, Shell Global Solutions US Inc. and Suncor Energy Inc. The conclusions in this report are those of the authors and are not necessarily the view of the other member companies. J.W. Carey wishes to acknowledge additional support from DOE-Fossil Energy (04FE04-09). Support for S. Gasda has been provided by a research fellowship through the King Abdullah University of Science and Technology (KAUST).Special thanks to Charles Christopher, BP Alternative Energy, for the guidance in creating this comprehensive program. Special thanks also to Ray Wydrinski, BP America for support with petrophysical analysis. Special thanks also to Andrew Duguid, Ph.D., and Matteo Loizzo of Schlumberger Carbon Services for their support in this project.

Publisher
Elsevier BV

Journal
International Journal of Greenhouse Gas Control

DOI
10.1016/j.ijggc.2009.10.010

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