In this study, we investigate multiphase flow phenomena in fine-grained rocks by measuring effective permeability of a suite of shale samples to gaseous ethane over a range of pore pressures up to the saturated vapour pressure (3.59 MPa at 18[degrees]C).
If d is in the mesopore range, the main fluid flow conduits can be completely blocked due to capillary condensation at pore pressures near to the saturated vapour pressure .
Such data indicate that the main flow conduits have minimum pore throat sizes in the macropore size range that are not completely blocked off at ethane pressures near the saturated vapour pressure (Figure 12(b)).
The mesopores are completely blocked off due to capillary condensation at ethane pressures near the saturated vapour pressure (Figure 12(d)), resulting in ethane gas permeability that is very sensitive to pore pressure.
Because pores in fine-grained sedimentary rocks are generally of submicrometer length scale, significant liquid/semiliquid ethane saturation exists due to adsorption and capillary condensation at ethane gas pressures near the saturated vapour pressure. The liquid/semiliquid ethane causes restrictions and blockages of flow pathways and therefore reductions to the flow capacity of fine-grained sedimentary rocks.
Samples with dominant pore sizes in the mesopore range are far more sensitive to ethane gas pore pressure because capillary condensation causes complete blockage of the main flow conduits at pore pressures near the saturated vapour pressure.
SVP is saturated vapour pressure. Data from Lemmon et al., 2017.
The ethane saturated vapour pressure at the temperature of the permeability measurements (18[degrees]C) is 3.59 MPa.