Page 210 - Origin and Prediction of Abnormal Formation Pressures

SEISMIC METHODS OF PRESSURE PREDICTION 185
dt, lasec/m (log ~0)

o
r -
o
_9
E
xi
13.
(D

Observed Profile

Pressure gradient

Fig. 7-9. Calculation of pore pressure by determining the intercept of the observed pressure profile and the
trend lines for the normal pressure. (Modified after Lindsay and Towner, 2001.)

0.20

0.15
0.I0
0.05
d.) Incidence angle
"t3 0.00
.i
Q. -0.05
E
<
-0.10
AVO at control well
m0.15
0.20
Fig. 7-10. AVO models at the prospect for different rock property models.

deep-water model showed that the pore and fracture pressures were very close. To
calculate the fracture pressure, one needs the horizontal stress which may be determined
using Poison's ratio (Eq. 7-4). Based upon empirical information (Eqs. 7-5 through 7-7),
a Poisson's ratio was chosen that started with 0.4 at the sea bottom and ended with 0.25
at a depth of approximately 4000 m. For the shallow-water model, the fracture pressure