Geology Reference
In-Depth Information
of the sediment cover. All known accumulations are controlled by large
faults with which oil and gas accumulation zones are connected.
Typical of the basin is the section's high oil- and gas-saturation com-
pared with its relatively small size. Over 90% of the discovered accumula-
tions are found in the upper section (depths up to 2,000 m). Almost the
entire clastic Neogene and Paleogene-Triassic of the lower structure-facies
stage include commercial oil and gas accumulations. What is interesting
is that wherever the upper complex is commercially productive the lower
stage is always hydrocarbon-saturated.
A certain zoning is established in the oil and gas accumulation distribu-
tion. Mesozoic reservoirs of the lower stage include mostly gas (gas-con-
densate) accumulations with the oil accumulations associated with erosion
buttes. In the Neogene series, the Miocene (the middle zone) includes
mostly oil and the Pliocene rocks, mostly a methane gas. The upper gas-
saturated zone is strongly faulted so its value is limited. The oldest pro-
ductive horizons are discovered in the Jurassic and Triassic rocks. The
Triassic includes a number of gas (Aderklaa, Baumgarten, Schönkirchen-
Über Tief and Reiersdorf ) and oil (Schönkirchen-Tief and Protess-Tief )
accumulations. In the Jurassic, small oil accumulations are discovered at
the Aderklaa, Breitenlee and Strasshoff-Tief prospects. In the Cretaceous,
gas accumulations are found at Aderklaa, Breitenlee, Protess-Tief and
Schönkirchen-Über Tief and oil accumulations at the Protess-Tief. The
Eocene flysh rocks, which are also included into the lower structure-facies
complex, are productive in the Sankt Ulrich-Hauskirchen field.
The largest hydrocarbon accumulations in the upper stage are discov-
ered in the Matzen, Zwerndorf, Schönkirchen, Aderklaa and Mühlberg
fields. The lower stage accumulation are mostly massive-type; stacked
fields of the upper stage as a rule include fault- and facies change-bounded
anticlinal accumulations.
1.1.4
The Irrawaddy-Andaman Basin
This basin is a sub-longitudinally elongated intermontane trough. It is sep-
arated from the adjacent mountains of Arakan-Yoma-Naga (in the north-
western part of the basin), of the Pusat Gayo Range on the plunge of the
Sumatra anticlinorium, of the Pematangsiantar highlands in the south, the
Shan Plateau and the Malacca Peninsula ridges in the east by large regional
faults defining a step-block structure of the area (Figure 1.6).
The sediment fill of the basin is mostly Cenozoic. The sediment cover is
9 to 10-km thick with about 70% being clays.
