Relative Permeability of Mudstones and Implications for Migration Modeling

Kuncho D. Kurtev and Andrew C. Aplin
University of Newcastle, Newcastle upon Tyne, United Kingdom

Oil and water relative permeability curves are critical inputs to Darcy-based, two phase migration models. The lack of relative permeability curves for mudstones imposes real limitations on, for example, the quantification of leakage rates through mudstone caprocks and the rates of primary migration.

Here, we present a new capillary pressure – saturation model which we have used to derive relative permeability curves of mudstones from MICP data. The curves are very different to those typically seen in sandstones; flow of the non-wetting phase is predicted at saturations below ten percent, and crossover points of the water and oil relative permeability curves occur between sixty five and eighty percent wetting phase saturation. Our data suggest that the relative permeability curves of mudstones diverge increasingly from those of sandstones as the lithologies become increasingly fine-grained. This confirms and extends the empirical data presented by Okui and Waples (1993).

We have compared our relative permeability curves with those calculated from pore network models with pre-defined networks of connected tubes of known dimensions. Curves similar to ours are derived when networks have coordination numbers of around three (typically six for sandstones), and high ratios of pore body to pore throat radius. Lenticular pores with restricted interconnections are inferred. Agreements between the results of two theoretical and one empirical approach lend confidence to the proposed relative permeability curves; migration through fine-grained sediments can now be more confidently modelled.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005