Geoscience Reference
In-Depth Information
Fig. 2.17
Distribution of oil and gas fields and shows in the Baltic basin
Most of them are oil accumulations, but offshore Poland gas accumulations also do
occur.
In the Kaliningrad district, oil production began in 1975. Currently 5-6 Mbbl
per year are produced from the onshore fields. Production from the offshore D6
oil field started in the second half of 2004. The Lithuanian onshore oil production
started after the restoration of independence in 1991. It reached the production peak
in 2004 with 2.8 Mbbl. There is light oil and gas production in the Polish sector of
the Baltic Sea. In the northern part of the basin, there is a small-scale oil production
in Gotland. In Latvia, several small oil accumulations were discovered. Only very
minor, short time oil production took place in 1990.
2.7.2 Major Reservoirs
The major hydrocarbon reservoirs are sandstone horizons of Middle Cambrian
age. They are underlain by Middle Cambrian shales and are capped by shales
of Ordovician-Silurian age. The total thickness of these sandstone reservoirs is
between 50 and 70 m. They are represented by shallow marine quartz sandstones
with subordinate shale and siltstone layers. The mineral composition of the sand-
stones is dominated by quartz that composes 96-99.8% of the rock volume. The clay
content varies between 0.5 and 3.5%. Illite commonly dominates the clay admix-
ture of the lower part and kaolinite predominates in the upper part of the reservoir
sections. This is related to either a regression phase or a more intense percolation
