Page 329 - Origin and Prediction of Abnormal Formation Pressures

298 V.A. SEREBRYAKOV, G.V. CHILINGAR AND J.O. ROBERTSON JR.

TABLE 11-1
Coefficient of irreversible compaction for various basins
Basin (source) Depth Coefficient of irreversible
(m) compaction/~ (t, T) x 103
(mPa-~ )
Gulf Coast, USA 0 0
(Dickinson, 1953) 1000 101.5
2000 24.6
3000 14.8
4000 14.5
Oklahoma 0
(Athy, 1930) 1000 98.0
2000 51.0
West Kuban Depression, Russia 0
(Popov, 1970, personal 1000 66.0
communication) 2000 42.0
3000 29.0
N. Caspian, Russia 0
(Dobrynin and Serebryakov, 1978) 1000 28.2
2000 21.1
3000 26.6
4000 26.3
Powder River 0
1000 30.4
2000 30.9
3000 25.0
4000 24.4

due to significant subsidence and aggradation, or uplift and erosion. The existence of
abnormally low pressured zones due to global temperature change at the Earth's surface
was first observed in eastern Siberia at a depth of 2.0-2.5 km near the crystalline
basement by Dobrynin and Serebryakov (1989). This phenomenon was also discovered
in other parts of the former USSR (C.I.S.): the Volga-Ural Province, northern part
of West Siberia, Ukraine and Georgia. Mostly, this phenomenon is attributed to the
changes in temperature at the Earth's surface during geologic time, with consequent
changes in hydrogenetic processes in geologic sections with compacted rocks (eastern
and western Siberia). In the Ukraine and Georgia, abnormally high and abnormally low
pressures are caused by subsidence and uplift, respectively. The theoretical basis of this
phenomenon can be analyzed as follows. At a certain time in the basin's history, there
was a hydrologic equilibrium defined by"
p l _ gPw (h - hst) (11-4)

where pl is the pore pressure, g is the gravitational acceleration, Pw is the average
density of water, h is the depth, and hst is the depth of the static water level. At a later
time, the depth changed. The overburden pressure ~r changed because of subsidence,