Leverett’s function (Leverett, 1941; Udell and Fitch, 1985)
Pcap=−P0⋅σ(T)⋅ f(Sl)
with
σ(T) - surface tension of water (supplied internally in TOUGH4)
f(Sl)=1.417(1−S∗)−2.120(1−S∗)2+1.263(1−S∗)3
where
S∗=(Sl−Slr)/(1−Slr)
Parameters: P0= CP(1) Slr= CP(2)
If CP(3) ≠ 0,
Pcgn=Pcap(=Pcgl)
Pcap(Pcgl)=0