Читать книгу Geophysical Monitoring for Geologic Carbon Storage - Группа авторов - Страница 78

Saturation of the pore space by scCO₂ was determined by obtaining CT images of the cores for (1) initial dry state (pore space filled with air), (2) water‐saturated state, and (3) partially scCO₂ saturated state. Knowing the densities of the fluids contained in the pore space, the average scCO₂ saturation within each CT imaging voxel was computed via linear interpolation.

For intact cores (Fig. 5.7, top left columns), scCO₂ migrated more or less uniformly but with higher saturations within layers containing larger pores (because of the stronger capillary entry pressure in the smaller pores) along the bedding planes. For core‐parallel fractures, the mated fracture (Frac Ia) contributed to somewhat localized distribution of scCO₂. However, the scCO₂ was still well dispersed throughout the core, possibly because the void space within the fracture was highly disconnected and did not result in an efficient fast path for the scCO₂.

In contrast, for core‐parallel fractures with large shear displacement (Frac Ib and Frac Id are shown in Fig. 5.7), almost all the scCO₂ migrated through the fracture, and little scCO₂ infiltrated into the rock matrix. Also, because of the large aperture of the fracture (~0.54 mm), the vertically oriented fracture in Frac Id exhibited preferential pooling of lighter scCO₂ in water along the top edge of the fracture by the buoyancy effect.

For a core‐perpendicular fracture, the migration behavior of scCO₂ was initially similar to the intact core, exhibiting a wide distribution of the fluid across the core with preferential flow along the bedding planes. However, the fracture (aperture ~0.26 mm) served as a trap and accumulated scCO₂ before the second half of the core was infiltrated.