Water Satuation

Low-permeability gas sandstones are typically characterized by high capillary pressure and high “irreducible” water saturations (S_iw). For both the Council Grove carbonates and
Mesaverde-Frontier sandstones, S_iw increases rapidly with decreasing porosity below 6-8% and can be characterized by the relations:

where S_iw and _i are in percent. In general, at any given porosity, Council Grove carbonates exhibit “irreducible' water saturations that are 5-10% less than Mesaverde- Frontier sandstones. This is probably due to the increased clay content and greater surface area of the sandstones.

For both Council Grove and Mesaverde-Frontier sandstones, S_iw increases gradually with decreasing permeability to k_i values between 0.01 md and 0.1 md. Below this permeability,
S_iw increases more rapidly with decreasing k_i, reaching values greater than 50% in rocks with k_i less than 0.001 md:

where S_iw is in percent and k_i is in md.