(496a) Risk Assessment for CO2 Geologic Sequestration

Sequestration of CO2 in existing and abandoned oil reservoirs, deep saline aquifers, and coal seams are currently among techniques intensely studied by the international research community for their potential to reduce greenhouse gases. In the case of sequestration to abandoned oil reservoirs, CO2 is pressurized and stored in these reservoirs, and a cement plug is placed at the bottom of the injection well. This cement plug, combined with an impermeable layer of caprock, creates a seal for the storage system, thus preventing CO2 from escaping.

A main concern for any sequestration system is whether it may leak CO2 over a long-term time horizon consisting of up to many thousand years. The outcome depends on the competition between CO2 sequestration and leakage processes. Leakages after sequestration in an abandoned reservoir may occur from failure of the manmade cement seal, or through naturally existing fractures in the caprock. Additionally, the CO2 source pool may be dissolved into formation water or migrate to water of surrounding formations. On the other hand, chemical reactions, such as mineralization, may prevent leakage. Modeling all these processes from first principles, while possible, requires knowledge of a number of parameters, such as various permeability and porosity values, that are not known with certainty. This motivates the development of simulators that can accurately deal with uncertainty in model parameters.

A number of simulators, including CQUESTRA [1, 2] and CO2-PENS [3], have been developed to assess the long term risk of CO2 sequestration. Monte Carlo (MC) simulations have been used in the context of these simulators to assess the uncertain behavior of sequestration processes. The main challenge in this context is that MC simulations are computationally demanding due to the large number of required iterations to produce a statistical representation of the output. In this work, we use a Graphics Processing Unit to parallelize the application of MC simulation to sequestration process models. We have implemented a sequestration simulator, mostly following [1] and [2], and used nVidia's Compute Unified Device Architecture (CUDA) [4] to develop a parallel MC implementation. Extensive computational results will be presented, illustrating that the proposed methodology provides a reliable and effective tool for performing sequestration studies, including assessing the effect of uncertain parameters and model equations.

References:

1. D. M. LeNeveu, ?CQUESTRA, A Risk and Performance Assessment Code for Geological Sequestration of Carbon Dioxide,? Energy Conversion and Management, 49(1), 32? 46, 2008.

2. F. B. Walton, J. C. Tait, D.M. LeNeveu, M.I. Sheppard, ?Geological Storage of CO2: A Statistical Approach to Assessing Performance and Risk,? Proceedings of 7th International Conference on Greenhouse Gas Control Technologies, 2004

3. P. H. Stauffer, H. S. Viswanathan, R. J. Pawar, and G. D. Guthrie, ?A System Model for Geologic Sequestration of Carbon Dioxide,? Environmental Science and Technology, 43 (3), 565-570, 2009.

4. V. Podlozhnyuk, and M. Harris, ?Monte Carlo Option Pricing,? nVidia Corporation Tutorial, June 2008.