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 * TECHNICAL INFORMATION  *


Modelling

(CO2SINK Work Packages 2.1 and 6.1)

Subsurface Modelling

A simulation model to predict the movements of the CO2 injected into the reservoir will be an essential part of the scientific programme. This model will be constructed using dynamic flow behaviour modelling; an activity that is designated as work package 6.1 in the overall plans.

Goals

Numerical modelling and simulation will address three important issues associated with the subsurface CO2 storage plans for CO2SINK. It will

  • Allow simulation of what-if scenarios using data on the Ketzin site. This will assist in planning and in the design of the subsurface storage facility. The simulation activities will run in parallel with the injection experiments.
  • Reveal the long-term fate of injected CO2 in the subsurface at this site in terms of plume evolution, phase changes, pressure evolution, chemical reactions and their influence in the porosity-permeability evolution.
  • Support risk assessment and safety questions related to seal integrity and the invasion of other formations by CO2-rich fluid.

Research approach

At present, there is no universal modelling tool that can simulate the complex, coupled temperature- and pressure-dependent process of multi-component, multiphase fluid flow in the subsurface and the chemical water-rock interactions and phase changes that accompany these movements.

The project at Ketzin will adopt and further develop existing modelling capabilities. Separate modelling of selected processes will reveal their effects at relevant space and time scales. Integrating the outcomes of the various tools in a joint interpretation will deliver a fresh insight into the relationships between these disparate processes.

Numerical work will be performed with programs that are commercially and publicly available.

Numerical Tools

The program system MUFTE_UG (MUltiphase Flow Transport and Energy model and Unstructured Grids (Helmig et al., 1994) was developed by the University of Stuttgart, Germany. It will be used to follow the injection of supercritical CO2 into the subsurface and monitor phase change and dissolution into the brine, spatial distribution, the resulting fluid flow pattern and possible invasion into leaky cap rock.

The University of Stuttgart participates in the international code intercomparison study for geological storage of CO2 organised by the Lawrence Berkeley National Laboratory in the USA.

SHEMAT (Simulator for HEat and MAss Transport) was developed by Aachen Technical University, Germany. SHEMAT is a reactive transport code (Clauser, 2003) that can address problems of coupled fluid flow, heat transfer, species transport and chemical rock-water interaction in fluid-saturated porous media. It uses a novel relationship that allows changes in porosity caused by chemical precipitation or dissolution to be mapped out into permeability changes.

TOUGH2 is a general-purpose multiphase-flow simulator. TOUGHREACT (Pruess et al., 2001) is a reactive geochemical transport model. The TOUGH family of codes has a large, international user community and will be used to simulate subsurface fluid (liquid and gas) flow and chemical (water-rock) interactions.

ECLIPSE is an oil industry standard reservoir simulation package for reservoir engineering problems. It is a finite difference simulator with several packages that allow users to model for effective reservoir management, including enhanced oil recovery techniques.

These codes complement each other in their modelling capabilities and represent a variety of numerical approaches.

Partners

University of Stuttgart - MUFTE-UG, SHEMAT

Shell International Exploration and Production - TOUGH2, TOUGHREACT

Geological Survey of Denmark and Greenland - ECLIPSE

NORSAR

Activities

The following activities are essential to the project:

1. Translate the geological model of the Ketzin site into a numerical grid that can be shared among project partners.
2. Create a background model that shows temperature distribution and flow field in the absence of CO2. This will include the mineralogical composition of the reservoir rocks and chemical composition of formation fluids. This model will provide the unperturbed initial state against which all simulations can be compared.
3. Small-scale numerical study of CO2 injection. This exercise will precede the first small-scale CO2 injection planned at the Ketzin site. The numerical study and the small-scale injection programme that follows it will guide the long-term injection strategy.
4. Numerical study of fluid rock interaction. The presence of CO2 may promote dissolution or precipitation, depending on fluid and rock compositions. The key rock types in the reservoir and cap rocks will be subjected to CO2-enriched brine so that the team can track changes in mineralogy (dissolution and precipitation) and the associated evolution of pore space and permeability. The aim is to assess the sensitivity of the rocks when exposed to the fluids and to evaluate the chemical integrity of the cap rocks.

These activities are planned for the first 18 months of the project. After reaching this milestone, further activities (A, B, C and D) are planned for the remainder of the project. The detailed scope for these activities will depend on the results of the modelling performed during the first project period. New data and information gained from the field operations (such as geophysical surveys, logging, core analysis, injection tests and seismic monitoring) and laboratory experiments will be incorporated into the model as they become available. The dialogue and feedback with other work packages in the project will allow the project team to incorporate these activities more precisely.

A. Conduct long-term hydrodynamic modelling of the fate of CO2 over the entire injection period and after injection has ceased. This activity will also examine phase changes, plume evolution and dissolution of CO2.
B. Track long-term chemical changes in fluids, host rocks and cap rocks.
C. Create a best practices guide for addressing modelling issues related to CO2 sequestration in saline aquifers.
D. Contribute towards the catalogue of features, events and processes (FEPs) to be incorporated in the risk assessment work package.

References

Helmig,R., Class,H., Huber,R., Sheta,H., Ewing,J., Hinkelmann,R., Jakobs,H. and Bastian, P.: Archi-tecture of the Modular Program System MUFTE-UG for Simulating Multiphase Flow and Transport Processes in Heterogeneous Porous Media, Mathematische Geologie, Band 2, 1998.

Clauser, C. (ed), 2003. Numerical Simulation of Reactive Flow in Hot Aquifers using SHEMAT/Pro-cessing Shemat. Springer Verlag, Heidelberg-Berlin.

Pruess, K., Xu, T., Apps, J. and Garcia, J., 2001. Numerical modeling of aquifer disposal of CO 2 . SPE/ EPA/DOE Exploration and Production Environmental Conference, San Antonio, USA, 26-28 February, Soc. Petroleum Engineers, SPE Paper 66537, 16pp.

LINKS

University of Stuttgart - http://www.iws.uni-stuttgart.de/forschung/projekt.php?Projekt=97&Abteilung=

MUFTE-UG - http://www.iws.uni-stuttgart.de/institut/hydrosys/sonstiges/mufte/

International Code Intercomparison study - Pruess K., Garcia J., Kovscek T., Oldenburg C., Rutqvist J., Steefel C. and Xu T., Code intercomparison builds confidence in numerical simulation models for geologic disposal of CO2, Energy, Volume 29, Issues 9-10, 6th International Conference on Greenhouse Gas Control Technologies, July-August 2004, Pages 1431-1444.

SHEMAT - http://www.rwth-aachen.de/geop/html/Software.htm

Aachen Technical University - http://www.rwth-aachen.de/geop

TOUGH2 - http://esd.lbl.gov/ITOUGH2/

TOUGHREACT - http://www-esd.lbl.gov/research_sums_02-03/climate/xu.html

ECLIPSE - http://www.sis.slb.com/content/about/campaigns/ brownfield/eclipse_options.asp?

Shell International Exploration and Production - http://www.shell.com/home/Framework?siteId=eandp-en

Geological Survey of Denmark and Greenland - http://www.geus.dk/geuspage-uk.htm

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