Evaluation of pore size distribution via fluid-fluid displacement porosimetry: The viscous bias

Fluid-fluid displacement porosimetry (FFDP) is a method for determining the pore size distribution of a porous medium from viscous fluid-fluid immiscible displacement (drainage) results, using a simplistic representation of the pore structure by cylindrical parallel tubes. The method leads to unambiguous estimates when the porous medium microstructure is strongly anisotropic and reasonably akin to this representation. The information obtained from this technique is however less straightforward to interpret for more complex microstructures. On the basis of synthetic data obtained from pore network simulations, it is evidenced, in particular, that this method leads to a shift in the distribution toward unrealistic small pore sizes. The shift, that may be very significant, is due to the viscous pressure drop in the displacing fluid. It is shown that significant improvement is achieved when the characterization of the pore size distribution is considered as an inverse optimization problem. The latter is solved using an optimization method presented in a previous work that was restricted to situations where viscous effects are unimportant.

Automated summary

Fluid-fluid displacement porosimetry is a method for determining the pore size distribution of a porous medium using cylindrical parallel tubes. It is effective for anisotropic structures similar to the representation used, but interpretation becomes more difficult for complex structures. The characterization of the pore size distribution can be significantly improved by considering it as an inverse optimization problem.