Page 54 - Geology and Geochemistry of Oil and Gas

CAPROCKS 31

Fig. 2.6. Diagrams of caprock breakthrough potential: (a) Type 1; (b) Type 2; and (c) Type 3. (In:
Eremenko and Chilingar, 1996.)

is the coefficient determining the distance between the base of the caprock and the
surface of maximum pore pressure. In this expression, P w.u.layer and P w.l.layer are,
respectively, the water potentials of the upper and lower layers.
Oil and gas accumulations have higher potential energy than that of the formation
water. These accumulations can be stable only if this energy is equal to or less than
the caprock breakthrough energy, i.e., P b P a , where P a is the total potential energy
of the accumulation. Total potential energy of the accumulation may be determined
from the following equation:

h
Z
P a ¼ P wr þ DgðhÞH G o H (2.15)
0