Page 42 - Origin and Prediction of Abnormal Formation Pressures

ORIGIN OF ABNORMAL FORMATION PRESSURES 25

0 psig
0'
i 0.433 psia,
v 1
...... 'i ......
i
|
I I
i | | |
0.867 psig 2'
ooi, ,I,,,,,,,
.... i i
i i
i i
i i
i i
1.3 psig
3'
"~ i :
i i
,,,,4' '~',oo 1.733 psig 4, . .....
"" i E ""
i i
i |
1 :
1 :
D =10fl ooot' '~',,, 2.167 psig5, . . . . . . . . ~'~
"" i i ""
i i
i i
i i
i i
i i
| i
.
Ii III I ~I iii iI ,Iii 2.6 psig 6' 9 .......
.... + | 1 i "'
i i
: 1
i i
: 1
.
Ii ii 41 1 I~iIi I 3.033 psig 7 ...........
9 ."" + : "",,
I i
i i
1 1
l 1 . ~
.
...... 'i ...... 3.466 psig8, 9 ..........
i i
i i
i i
i i
3.9 psig
,,,,4" ,I,,,,
9'
, : 1
1
i i
4.333 psig
2 3 4 5
l in? ~" ~---1 in. Pressure, Ph, psig
Fig. 2-1. Pressure versus depth for a 0.433 psi/ft gradient (pure water). (Modified after Brown, 1967, fig.
3.11, p. 28; in Khillyuk et al., 2000, fig. 18-1, p. 269.)
water with the salinity of 80,000 parts per million (ppm) of sodium chloride at 77~
(25~
Sediment consolidation
The forces acting on a unit of sediment control its compaction. Terzaghi and
Peck (1948) were early pioneers in the study of compaction; however, the geologic
applications of the theory of compaction of fine-grained clastic sediments was first
elucidated by Hubbert and Rubey (1959).
In nature, the load acting on a unit of sediment is carried by the (1) skeletal
framework and (2) the interstitial fluid in the pores. The total stress at any point
consists of the sum of two stress components: the skeletal (intergranular) stress and
the pore-fluid stress. The term effective pressure, Pe, is used to designate the difference
between the total overburden pressure (geostatic or lithostatic) and the pore pressure,