Geology Reference
In-Depth Information
litho-reservoir and other conductive unconformities pro-
viding for the drainage are a necessary condition for the for-
mation of oil and gas occurrences.
5. Close to optimal ground water discharge conditions from
relatively shallow reservoirs (down to 2,000
2,500 m) deter-
mine in all regions the concentration of major hydrocarbon
reserves (about 85%) within this depth range. They also
limit the probability of presence at great depths (deeper
than 3,500
−
4,000 m) of large oil and gas accumulations. The
mentioned depth interval has limited emigrational water-
exchange and for this reason low likelihood of void volume
and large oil and gas accumulations.
6. Oil- and gas-saturation within regional oil and gas accumu-
lation zones and individual productive structures is usually
secondary. The major commercial hydrocarbon reserves
are associated with areas and intervals of contrasting cross-
flow-injection hydrochemical, geotemperature, piezometric,
isotope and palynologycal distortions of the corresponding
fields. The fields are generated by vertical interformational
fluid migration from deep generating zones of the sedimen-
tary section into the upper accumulating natural reservoirs.
−
