Page 277 - Origin and Prediction of Abnormal Formation Pressures

PORE WATER COMPACTION CHEMISTRY AS RELATED TO OVERPRESSURES 249

S 2000 6000 10,000 14,000 18,o00 Salinity, ppm
T 230 ~ 2 5 - ~ - - 27:0 ~ --- 29,0 ~ 310 ~ Temperature, ~
Age pp 5500 6300 7100 7900 87p0 Pressure, psi
Mud weiqht
_
9 30" CSG @ 146 m
Sp. Gr.
". 20" CSG @ 424 m
Pliocene --
Pleistocene

1000
-1.32
b 13-3/8" CSG @ 1463 m

2000 _
?:T_
-1.12 to
r- -i Normal pressure 1.18
-..
';-~~ IL9.5/8,, CS'~"~K, ~ ~....,. ~ ~ AHFP _--- --~ -1.58
~ @ 2761 m --" .... ~,~ "" --- "----,. "~ .,~,,,
. . . . . .
s ha~-rt
a~176176 ', \\ \ ~.
I
Lower ~ ~.
Oligocene
Middle
Eocene
g
4000- ~ ~--rLr~rL~
\T
(324 ~
~8
~ T D = 4752 m

Fig. 10-11. Plot of pressures, salinity and temperature data in the offshore Kutch well, Kutch Basin, India.
(Modified after Sahay, 1999, fig. 11-69, p. 312.)

history in the Songliao Basin. This investigation examined the vertical characteristics
of underpressure, pore fluids, and sealing conditions in the Shiwu Fault Depression.
The depression is part of the Songliao Basin, Jilin Province, northeastern China.
Pore-pressure data were obtained from drillstem tests in 40 wells, and chemical analyses
were performed on 84 pore-fluid samples. Table 10-4 presents the pore-water chemistry
data for both the normal and subnormal pressure zones.
Hydrochemical data profiles demonstrate that the ionic evaporite trends of the
pore water in the underpressure zone are different from those trends in the overlying
sediments, which normally are a hydrostatically pressured sequence. This indicates
that the underpressured system is sealed. The pressure transition is sharp and there