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Abstract: Abnormal Pressures in the South Caspian Basin

Djevanshir Rashid, Aliy Arov Rauf, Kazieva Mafizat, Akhverdiev Allakhverdi

The South Caspian sedimentary basin is a classical example of an elision water drive basin with intensive development of abnormal pressures.

The factor of gravitational sediments consolidation plays the basic role in abnormal pressures genesis in the South Caspian basin characterized by a high rate of sediments, mainly clayly ones accumulation.

The analysis of the results of pressure estimates carried out on the basis of the data on geophysical well testing and surveys over 42 deposits has allowed to set up regularities of changes in abnormal pressures intensity both in a regional area, and in respect to depth.

Three peculiar intervals with different intensity of pore pressures development are distinguished in regions of northern and western parts of the South Caspian basin in a geological section. The first interval refers to the upper part of the productive series of Middle Pliocene including Surakhany, Sabunchi, and Balakhany suites, the suite of "Pereriv", and their analogous; the second is the lower part of the productive series including NKG, NKP, KS, PK, and KaS; and the third one is sediments underlying the productive series or Lower Pliocene (Pontic stage) and Oligocene, i.e. Miocene complex. This interval is characterized by the most intensive development of abnormal pressures.

Within the intervals one can distinguish ones with relatively low pressures which refer to regionally developed arenaceous horizons.

In the regional area there exists a tendency towards increasing pore pressures in clays from deposits of the Apsheron peninsula in the South and South-Western directions to the regions of the South-Apsheron zone, Baku archipelago, Prikurinskaya and Shemakha-Kobystan district, and in the east direction to the deposits of the Pribalakhany area.

Interconnections between abnormal pore pressures and lithology, and mineralogical composition of sediments, their depth of occurance, tectonic conditions are studied and established.

Peculiarities of the effect of internal water drive on the change in physical parameters of deposits with abnormal pressures are investigated.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France