Page 84 - Petroleum Geology

Formulae for obtaining porosity and pore pressure in mudstone from sonic transit
time (At in ps/ft)
1. f = fo (At - Atma)/(Ato - Atma)
2 (At - 55)/220 (5.7)
2. At = (Ato - Atma) e-6z/b + At,,
z 110 e -216 + 55 ps/ft (3.8)
3. b = -6 z/ln {(At - 55)/(At0 - 55)} (units as z (3.9)
4. 6 = -(b/z) In {(At - 55)/(Ato - 55)}
5. ze = 6z = -b In {(At - 55)/(At0 - 55)) = bz*
6. z* = 6 z/b = --In {(At - 55)/(Ato - 55)}
7. Estimated maximum pore pressure in mudstone:
imax = hS = (1-0.556) ybwz
2: (1 - 0.556) 22.63 x z MPa
hmax = (fi/Y,)-z N (fi/10.18 x 103)-z m
8. Equivalent At for mudstone to balance mud specific gravity:
Atmud eq.= (At - 55) ex + 55 ps/ft
wherex = (z/b) { (s.g. - 2.3)/1.3 j

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