STUDY OF SOURCE ROCKS IN THE WESTERN NORTHEAST JAVA BASIN
Research area is located at western part of Northeast Java Basin where highly significant oil and gas accumulation has been discovered in this basin both offshore and onshore areas. Despite the recent significant discoveries, there are still many uncertainties concerning aspects of petroleum geoc...
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| Format: | Theses |
| Language: | Indonesia |
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| Online Access: | https://digilib.itb.ac.id/gdl/view/7532 |
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| Institution: | Institut Teknologi Bandung |
| Language: | Indonesia |
| Summary: | Research area is located at western part of Northeast Java Basin where highly
significant oil and gas accumulation has been discovered in this basin both
offshore and onshore areas. Despite the recent significant discoveries, there are
still many uncertainties concerning aspects of petroleum geochemistry in the basin
especially at western part this basin.
During the study geochemical data of oil and source samples comprising physical
to molecular properties from five wells and four seeps of the onshore areas of the
Northeast Java Basin were interpreted using various geochemical crossplots and
methods.
The oil and the source rock data from wells and seeps were tested according to
their availability of n-alkanes including their isoprenoids, triterpanes data, steranes
data, and carbon isotope. The biomarker data that have been used in this research
is limited only on common mass ion such as triterpanes (m/z 191) and steranes
(m/z 217). Based on those data, the oil – source rock correlation is made to
determine source rock that produced hydrocarbon.
According to the source rock richness and maturity analysis, The Ngimbang
clastic Formation in Rembang-1 is known for having a good to excellent degree of
richness as a source rock. The Ngimbang clastic Formation in the research area is
on the stage of early mature and has a preference to produce oil and gas which
comes from Type II and Type III kerogen.
The oil – oil correlation in the research area has divided the oil samples into two
oil groups. The first oil group is the oil group in which the organic material comes
from the mix of high plants and algae where the depositional environment of the
source rock for this oil group is more headed for shallow marine (deltaic?)
environment. The specific characteristics of this oil group are the bimodal peak
iv
shape of n-alkanes distribution at C17 and C27, the low ratio of phytane/pristane,
the subordinate portion of C23 and C26 tricyclic triterpanes, the presence of
nonhopanoid like oleanane, gammacerane and resins on pentacyclic triterpanes, a
dominant portion of C27 steranes, and the value of carbon isotope is smaller than
-5. The second oil group is the oil group in which the organic material comes from
more of the high plants where the depositional environment of the source rock for
this oil group is more headed for terrestrial environment. The specific
characteristics of this oil group are the one peak shape of n-alkanes distribution at
C27, the lower ratio of phytane/pristane, the abundance amount of oleanane and
resins on pentacyclic triterpanes, a dominant portion of C29 steranes, and the value
of carbon isotope is bigger than +4.
According to the C27-C28-C29 ternary plots from four oilseeps and extract source
rock from three wells there is positive correlation about oil from terrestrial and
Ngimbang clastics Formation, based on a visual comparison of triterpane (m/z
191) and sterane (m/z 217) distributions shows close similarities between Kedung
Jati oilseep and extract source rock (Ngimbang clastics Formation) in Rembang-1
well, this is suggestive of Kedung Jati oilseep being generated from the Ngimbang
clastics Formation.
The oil – source rock correlation in the research area shows that Eocene
Ngimbang Formation as a source rock that produced the terrestrial-shallow marine
(deltaic?) oil group. |
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