Pore-Scale Mechanism for CO2 Storage in a Fracture-Matrix System

When fractured reservoirs are selected as storage sites for carbon dioxide (CO2), it is desirable that sequestrated CO2 present in the fractures invades the matrix blocks and remains stored in the porous space. The occurrence of this mechanism is important to:
  • achieve optimal pore volume exploitation which in turn makes the storage safer and more efficient; and
  • avoid CO2 migration upwards through fracture systems which results in a less confined storage volume and, at worst, leakage which in turn may contaminate the surrounding environment.

In this project the objectives are to develop criteria for the occurrence of CO2 transfer between fractures and matrix blocks, and to compute capillary pressure curves for real fracture-matrix geometries which are required to model experimentally observed behaviour in such systems at the core scale. This will be achieved by the following research tasks:
  • Develop a 3D pore-scale model for the computation of the fluid distribution in the real pore geometry that constitutes a fracture-matrix system. The model will consist of two main components:
    • a 3D pore-scale model for the fracture based on the level set and variational level set method; and
    • an improved 2D semi-analytical pore-scale model for modelling the fluid distribution in the surrounding permeable fracture walls (i.e., the surrounding matrix blocks).
  • Obtain images of the real 3D pore geometry of matrix-fracture systems, including surface roughness of the permeable fracture walls, to be used as input in the newly developed computational procedures.
  • Use the pore-scale model to compute fluid distributions and capillary pressure functions in the fracture and matrix – both individually and combined – for different wetting conditions, initial fluid distributions and geometries (e.g., fracture aperture). The conditions under which CO2 enters the matrix blocks will be calculated to investigate the capillary seal efficiency of the overburden rock.

Finally, the criteria to be developed in this project will also be useful for increased oil recovery processes where CO2 is injected in fractured reservoirs to displace remaining oil from the matrix blocks.

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