Simulation of CO2 storage in coal seams : coupling of TOUGH2 with the solver for mechanics CODE ASTER

8 March 2013

Publication at the TOUGH Symposium - Lawrence Berkeley National Laboratory, Berkeley, California, September 17- 19, 2012

A. Loschetter(1), F. Smai(1), S. Sy(1), A.Burnol(1), A. Leynet(1), S. Lafortune(2) and A. Thoraval(2)

1 French Geological Survey (BRGM)

2 French National Institute for Industrial Environment and Risks (INERIS)

Amongst the various geological storage options currently under consideration, CO2 storage in coal formations presents the most economic potential for middle-term spreading but also the most uncertainties and technical difficulties. Indeed, the profit from methane recovery could cover part of the costs, but little testing for this technique has been conducted in European coal deposits. Therefore, there is a need for an in situ injection study at an intermediate scale between a laboratory and an industrial pilot. This is the aim of the CARBOLAB project [1].
This study investigates coupled flow and mechanical processes that will take place around the injection point at the bottom of the Montsacro mine in Asturias, Spain. Reservoir simulators, such as TOUGH2, have been used for CO2 storage in saline aquifers and oil and gas reservoirs (Oldenburg et al., 2004; Xu and Pruess, 2001). However, until now, this tool did not represent the adsorption process, a key point for explaining the gas storage and gas migration through coal seams. Moreover, CO2 sorption and exchange with adsorbed CH4 are associated with mechanical processes like swelling/shrinkage. In order to quantify the strain and stress fields due to changes in the fluid pressure field and to account for stress/sorption dependent porosity/ permeability effects, an efficient coupling between TOUGH2/EOS7C, a special module with an Extended Langmuir Sorption model, and the solver for mechanics CODE _ASTER® has been developed by BRGM. This new tool will be first verified by intercomparison with the COMSOL-based tool developed by INERIS and, afterwards, validated with in situ data acquired during the ongoing injection at the Montsacro mine.

Illustration of relations that enable coupling mechanic with thermo-hydrodynamic equations
Geometry and boundary conditions
(color red: hydrodynamic boundary conditions; color blue: mechanical boundary conditions)

Such a simulator could be used to understand better the very complex behavior of coals. The detailed impact of different parameter perturbations, both individually and simultaneously, in this highly coupled problem will be the subject of further research. The simulator could also be used for monitoring design, for injection scenario studies and for future project sizing.

[1] CARBOLAB is a project supported by the European Fund for Coal and Steel involving HUNOSA, owner of the mine, AITEMIN from Spain, BRGM, INERIS and TOTAL from France, GIG from Poland.