Page 107 - Origin and Prediction of Abnormal Formation Pressures

ORIGIN OF FORMATION FLUID PRESSURE DISTRIBUTIONS 87
Pressure gradient, MPa/m (psi/ft)

t3.010 0.015
(0.0431 ) (0.065)

500
(1,639)
1,000
(3,279)
1,500
(4,918)
2,000
(6,557',

l:::: 2,500
.ff (s,197)
~. 3,000
a 9 (9,836~
3,500
(11,475)
4,000
(13,115)
4,500
(14,75:13

5,000
(16,39.31)
Fig. 3-5. Average pressure gradients at the Southern [Yuzhnaya] (1), Sangachaly-Duvannyy-Sea-Bulla
Island fields (2) and Sub-Kura Depression (3). (Modified after Buryakovsky et al., 1986. In Gurevich and
Chilingar, 1995, fig. 3, p. 129.)

Apsheron petroleum zone has locally some noticeable abnormalities (Oil Stones,
Mud Cone, Zhiloy Island, Makarov Bank and other oil fields in the Apsheron
Archipelago and Lokbatan-Karadag in the southwestern part of the Apsheron Penin-
sula). Abnormalities in the upper and middle parts of the Productive Formation in this
zone exist mostly within the boundaries of oil and gas pools. Beyond these boundaries
pressure is mostly hydrostatic.
Shales with abnormal (calculated) pressure in the Apsheron Archipelago are first
encountered at a depth as shallow as 480 m (1574 ft) in the Peschanyy field in the lower
part of the Apsheron Formation (Yusuf-Zadeh et al., 1979). The pore pressure gradient
reaches 0.0158 MPa/m in the Akchagyl Formation and changes discontinuously with
depth. For example, pressure gradients in the Lower Surakhan shales are normal.
Reservoir pressures in the Apsheron Archipelago are about normal. Abnormal pressures