MINISTRY OF EDUCATION AND TRAINING
HA NOI UNIVERSITY OF MINING AND GEOLOGY
TRAN CHAU GIANG
CHARACTERIZATION OF THE CENOZOIC
PETROLEUM SYSTEM IN THE NORTHEASTERN OFFSHORE
SONG HONG BASIN
Subject area: Engineering geology
SUMMARY OF DOCTORAL THESIS WORK
The thesis work has been completed at: Ha Noi University of Mining
1) Professor, Doctor of Science. Mai Thanh Tan
2) Dr. Le Tuan Viet
Judge 1: Associate Professor, Doctor. Pham Huy Tien
Judge 2: Dr. Nguyen Huy Quy
Judge 3: Dr. Cu Minh Hoang
The doctoral thesis work will be defend at the University Council of
Scoring Thesis Meeting at the Hanoi University of Mining and
Geology at …….hour, day ……., month……year ……..
You can find out the thesis in the libraries: National Library, Hanoi
or Library of Ha noi University of Mining and Geology
Song Hong Basin is complex sedimentary basin, including several
tectonic elements with different oil and gas potential. The VPIIDENMITSU (2005-2007) project has confirmed non-marine dual
petroleum system (lacustrine and fluvio-deltaic) in the Song Hong
basin by advanced geochemical analysis. Due to no oil – source rock
correlation, the characterization of petroleum system in the
Northeastern offshore Song Hong basin has yet to be confirmed.
In 2008, the oil discovery by 106-HR-1X has proven the
hydrocarbon potential of the Pre- Cenozoic carbonate basement Play.
Next well 106-HR-2X was drilled through the oil reservoir bearing in
the Pre – Cenozoic carbonate basement and penetrated a thick shale.
It is a questionable that this Pre- Cenozoic shale is a new source
rock. Well 107-PL-1X drilled in 2013 in the rich organic source area,
and has the same structural trend as 106-HR prospects. However the
well was dry. Other latest exploration wells have discovered gas
condensate with heavy H2S and CO2 polluted in the reservoir fluid.
These facts show many issues have to resolved such as the quality
and distribution of source rocks, or which risk factor of geological
parameters in the petroleum system have affected the results of
exploration in the area of Northeastern (NE) offshore Song Hong
Therefore, the topic "Characterization of the Cenozoic
petroleum system in the Northeastern offshore Song Hong Basin"
was chosen with the objectives and research tasks are as follows:
- To get better understand about the characterization and area
distribution of petroleum source rocks of Cenozoic sediments in the
NE offshore Song Hong Basin.
- Contribute to improve the methodology for petroleum systems
evaluation and risk analysis in exploration.
- Integrate geological data and geophysical data to clarify the
regional geological setting.
- Research to clarify the characterization and level of maturity
and timing of HC generation and migration, identify the origin oil
generated source rock in the NE offshore Song Hong Basin.
- Determine the area distribution of source rocks and HC potential
Object and scope of the study:
The scope of the study include the block 106 area, Northwestern
of block 102 and North part of block 107 offshore Song Hong basin
that separated to others area by Song Lo fault. The objective to study
is Cenozoic petroleum system.
Thesis 1. Study results of the geochemical characterization
identified a lacustrine petroleum system related to the Oligocene
source rock exist in the NE offshore Song Hong Basin. The source
rock contains moderate to good organic richness, kerogen type II and
mixed type II/ III, locates in the grabens and half grabens within the
study area. Based on all available geochemical data of the Miocene
shale and Pre- Cenozoic shale that identifies these shales are not
qualified to be a source rock.
Thesis 2. Based on the study of factors impact on risk of the
petroleum system such the origin, maturity, the Oligocene sediment
thickness and the distribution of potential prospects, restore the
geological development through the ages that are enable to identify
the Thuy Nguyen graben has lowest exploration risk. Next is the
Kien An graben. The South Bach Long Vi Island area and NW edge
of block 102 are the areas of high exploration risk.
New findings of the thesis work:
- Based on latest exploration data, results of thesis work has
contributed accurately geochemical characteistics of the NE offshore
Song Hong basin. The Pre- Cenozoic shale below the carbonate layer
bearing oil has terrestrial lithoface, deposites under oxidizing
condition environment, with poor organic contain that is not
qualified to be a source rock.
- The new structural maps were built have contribution to get
better understand of Late Oligocene inversion event affect oil and
gas potential of the area of Northeatern Offshore Song Hong basin.
The scientific and practical contributions:
* Scientific contribution: The results of research allowed identify
the characterizations and the distribution of source rock to get better
understand of petroleum system in NE of Song Hong basin, offshore
* Practical contribution: Contribute to improve the effectiveness
of HC potential assessment for the NE of Song Hong basin, and to
serve the Oil companies in the exploration and exploitation activities.
The layout of the thesis:
The thesis consists of 04 chapters excluding the introduction and
conclusions, recommendations, papers publication and reference
lists. The entire content of the thesis is presented in 135 pages, 24
tables and 89 figures.
SUMMARY GEOLOGICAL STRUCTURE IN THE
NORTHEAST AREA OFFSHORE SONG HONG BASIN
1.1. Overview the geology of study area
Study location is part of
Northeast Song Lo fault offshore
Song Hong basin. Water depth
from 30-40m. (fig.1.1)
1.1.2. Exploration history
Fisrt exploration work began
in 1978. In 1988, first PSC was
signed for block 106, and a part
of block 102, 103 and 107
between PVN and TOTAL. In
1992, IDEMITSU – PVN signed
a PSC for block 102/91. Next the
blocks 102 – 106 with total area
Petroleum Inc in 2000. Recently,
this PSC has relinquished area
and maintained in area of 225
Fig. 1.1: Structural map of Top
basement Song Hong basin and
study area location (N.T.Dau. et
km2. The remaining area now is
block 102/10 and block 106/10 with PVEP operator. From 1990 to
present, in the study area were acquired more than 15,000 km of 2D,
and over 3000 km2 of 3D seismic, more than 10 exploration wells.
Several studies are available as Geochemical model of Song Hong
Basin (N.T Dau, L.V Hien, 1997), Outcroup study in Bach Long Vi
island, Do Son, Kien An, Elephant Mountain, and Cat Ba Island (P.Q
Trung, 1998), Investigate the amount of HC generated and migrated
from source rock to trap in the Song Hong basin by SIGMA 2D and
BSS softwares (N.T.B Ha, 2010), Final Report on the analysis and
modeling Song Hong Basin (VPI - GEUS, 2001), Report on
Characterization of petroleum systems in the Song Hong Basin by
State of the art Geochemical Technology (VPI-IDENMITSU, 2007).
1.2. Regional setting
stratigraphic units consist of: (i)
Pre-Cenozoic basement; (ii) Phu
Tien Formation (E2pt); (iii) Dinh
Phong Chau Formation (N1 pc);
(v) Phu Cu Formation (N12pc);
Formation; (viii) Formation of
Hai Duong - Kien Xuong (N2-Q)
There exist in the study area Fig.1. 2: Stratigraphic column of
02 fault systems. The NW-SE the offshore Northeast
and NE-SW fault systems.
basin (After N.T.Dau et.al, 2012)
These fault systems created structural type of dipping down to the
basin center and formed a series of grabens alternate half grabens.
The identified structural zonnation (Figure 1.3):
The shelf located in the
northeastern part of the
study area, covers a
large area of the block
106 and block 101.
Fig.1. 3: Fault systems and structural
monocline: It is located
to the West of the Song Chay fault.
Central trough: can be subdivided as
a) Miocene Inversion Zone
b) Dong Quan trough
North-East differentiated monocline: mades up of grabens, half
grabens, horsts, and basement uplifts. Detaily consists of:
a) Kien An Graben
b) Tien Lang - Chí Linh horst
c) Thuy Nguyen half graben
d) Trang Kenh Nose
e) Western Bach Long Vi trough
f) Yen Tu Horst
g) Southern Bach Long Vi trough
Tectonic evolution was constructed based on restoration cross
sections. The study results show the similarities and differences over
the period of development of the region on the two banks of Song Lo
Fault. In Paleocene-Eocene to the Early Oligocene and Pliocene –
Quaternary period are similar but different in period from late
Oligocene to late Miocene.
1.3. Data base
The documents use in thesis work are more than 15000 km 2D
seismic, gravity maps of the Bac Bo Gulf, Vietnam geological maps,
well logs and obtained rock samples were analyzed for the
Petrography, Geochemistry, and Biostratigraphy studies. Especially
with 500 m of core samples from Enreca – 3 well in Bach Long Vi
island to study sedimentary, litho-facies, and geochemistry of
2.1. Petroleum system and its role in oil and gas exploration
Petroleum system concept appears too many different definitions.
The term “system” includes source rock and reservoir rock, oil source correlation are considered a key factor in determining system
(Dow W.G, 1972). Synthesis of the concept put forward by many
authors, petroleum system is understood as a natural system where
exist generated petroleum source rocks with all the geological
elements and geological processes related to the ability to
accumulate oil and gas may occur.
In 1988, L.B Magoon had established a system classification,
which distinguishes the petroleum systems to sedimentary basins,
Plays and Prospects. Depend on the level of research, petroleum
system is evaluated as an overview to detail as scale of a country,
sedimentary basin, a play and to each independent prospect. The
basic methods of assessment can be summarized as follows:
+ Analysis petroleum system was evaluated on the basis of the
total volume of HC generated/rock volume by Exxon.
+ Analysis petroleum system was evaluated on the prediction of
petroleum geology characteristic (Delphi method), mainly based on
the experience of experts.
+ Analysis petroleum system was evaluated on Geochemical
material balance based on the calculation of the amount of oil and
gas generated from source rock, as well as oil and gas were migrated
and can accumulate in the trap.
+ Analysis petroleum system was evaluated on extrapolation of
+ Analysis petroleum system
by Play fairway analysis (based on
geological model and statistical
data) allows determine the change
of the geological factors related to
the oil and gas accumulation in an
Figure 2.1: Play concept
In the thesis work, Play assessment is applied to solve remaining
problems in petroleum system in the study area.
2.2. The geochemical methodology
Complex sets of geochemical index in evaluating the capacity of
HC generation of sediments used in the thesis are:
+ Combust a crushed sample of rock at 600ºC
+ Pyrolysis method Rock-Eval standards (RE)
+ Bitumen extraction method
+ Chromatography (GC)
+ Mass spectrometry analysis (GC-MS)
+ The vitrinite reflectance (Ro,%)
2.3. Geochemical modeling
reproduce the processes relating to
petroleum system in computer
from past to present time, which
enables to assess the timing and
location of generation, migration
and accumulation of Oil and Gas.
The soft ware used is SIGMA-2D.
Principles for SIGMA model is
explained detail as figure 2.2.
2.4. Petroleum system analysis
According to Magoon and Dow
(1994) to study a petroleum system
elements includeing: source rock,
Fig 2.2: SIGMA 2D outline
reservoir, seal and the overlying rock layer with the combination of
three processes are: the formation of oil and gas traps, the oil and gas
generation, migration and conservation of oil and gas after trapped.
2.5. Geological risk assessment
The purpose of risk assessment in petroleum system analysis is to
estimate the probability of discovery prior to drill of a prospect/play.
The probability of discovery is defined as the product of the
following major probability factors, each of which must be evaluated
with respect to presence and effectiveness. According to CCOP risk
assessment guideline, the 04 factors are: Reservoir (P1), Trap (P2),
Petroleum charge system (P3), and retention after accumulation (P4).
The probabilities of these factors are estimated with respect to the
presence and effectiveness of the geological process associated with
them. The probability of discovery is calculated using the formula:
P = P1*P2*P3*P4
P: Probability of discovery oil and gas (or probability of
simultaneous occurrence of the events associated with each
P1: The probability of the presence of reservoir rock includes: i)
P1a: Probability of existence of reservoir facies; ii) P1b: Probability
of effectiveness of the reservoir
P2: The probability of the presence of a trap includes: i) P2a the
probability of presence of the mapped structure and ii) P2b the
probability of effective seal mechanism for the mapped structure
P3: The probability factor for the petroleum charge system
includes: i) P3a the probability of effective source rock and ii) P3b
the probability of effective migration
P4: Probability of effective retention of HC in the prospect after
Tab.2.1: Probability of
existence of reservoir facies
Tab 2.2: Probability of
effective reservoir with depth
In essence, the probability of discovered of an object is:
P = P1a* P1b* P2a* P2b* P3a* P3b*P4
Probability value of each parameter is defined rely on subjective
knowledge, extrapolation from the analysis geological and statistical
data. Following the guidance of CCOP, for example, the tables 2.1
and 2.2 describe the probabilities of P1a and P1b parameters.
CHARACTERIZATION OF SOURCE ROCK IN THE
OFFSHORE NORTHEAST SONG HONG BASIN
3.1. Organic richness in source rock
+ Pre-Cenozoic sediments: very poor in organic matter and not
be generated oil and gas. TOC values from 0.03 to 0.05% weight.
Unmeasurable indicators S1, S2, PI, HI and Ro.
+ Eocene sediments: no wells confirm met Eocene.
+ Oligocene sediments: organic matter is moderate to good. 8/14
samples in 106-HR-1X well have TOC values> 1%. Samples on
Bach Long Vi Island with TOC values from 1.5 to 6.59%, 10/100
samples have S1 value from 0.08 to 1.19 mg/g, and 99/100 samples
with S2 > 10 mg/g, in average of 17 mg/g represented the organic
contain from good to very good.
+ Lower Miocene sediments: all samples get very low value, so
3.2. Kerogen type
+ Oligocene sediments: Figures 3.1a and 3.1b (N.T.B.Ha, 2010)
show the Oligocene (brown points) found in wells in block 107 and
Chi Linh –Yen Tu host with HI values <300mgHC/gTOC for
samples with low maturity distributed in kerogen type III. The
sample has a higher maturity distributed in kerogen type II. Source
rock is able to generate mixture oil and gas and have reach maturity
Figure 3.1a: Plot HI and Tmax by Figure 3.1b: Plot (S1 + S2 mg/g)
the structural zonnation in the and
Song Hong Basin (NTB Ha, zonnation in Song Hong Basin
(NTB Ha, 2010)
Results of the well ENRECA 3 on Bach Long Vi Island show
sample populations fall into the group of kerogen type II and I.
Oligocene sediments have oil prone with capability from fair to good
(Figure 3.2 a, b) .
+ Lower Miocene sediments: almost HI <200 mgHC/ gTOC,
kerogen type III, expressed in gas prone. Four samples obtained at
106-YT-1X shown capable of oil generation.
+ Middle Miocene sediments: HI value changes from 50 to <300
mgHC/gTOC, kerogen type III, with gas prone. Samples at 106 YT1X with HI values up to 456-520 mg/g, kerogen type II/III with both
oil and gas generation potential. The Mid. Miocene samples in 107PL-1X well are also have potential of both oil and gas generation.
Figure 3.2a: Plot HI and Tmax at
Figure 3.2b: (S1+S2 mg/g) và
well ENRECA 3
TOC % at well ENRECA 3
3.3. Depositional environement of organic matter
The HI vs TOC diagram (Figure 3.3), results of gas
chromatography (GC) (Figure 3.4) indicate depositional environment
of organic matter of Oligocene source rocks in the study area is
mainly lacustrine origin.
Results of gas chromatography (GC) from Oligocene, Lower
Miocene at 106-HR-1X, 106-HR-2X, 107-BAL-1X reflect the origin
of organic matter was derived from high plants (Figure 3.5a, b).The
Ts/Tm vs Oleanane/C30 Hopane diagram was used (Okui et al,
2007) to distinguish lacustrine petroleum system from fluvio-deltaic
petroleum system. This plot indicates the oil from Ham Rong field is
3.4. Maturity of source rock
+ Oligocene sediments: Vitrinite index (Ro,%) from well Enreca
-3 has value <0.4% and Tmax values from 410-440oC. Two shale
samples in well 106-HR-2X (3209-3917m) with Tmax values
measured 444-445oC are at oil window. Data reveal the Oligocene
sediments have varied thermal maturity level from low maturity to
+ All Lower and Middle Miocene samples from Ham Rong-Yen
Tu and Pha Lai wells are immature.
Figure 3.3: The diagram defines
environment of organic matter in
Song Hong Basin (points brown)
(NTB Ha, 2010)
Figure 3.4: The diagram
environment of organic matter
by Pr / C17 and Phy / C18 in
the study area (Ha, 2013)
Figure 3.5a: The
Figure 3.5b: Steranes C27-
28-29 triangle chart
Ts/Tm diagram of study area
3.5. Oil to source rock correlation
Oil sample from Ham Rong was analysed that shows normal
crude oil and displays API gravity of 39,220API, moderate wax
content (11,3%), moderate viscosity (4,058Cst) and moderately low
pour point (270C). This oil is low sulphur content (0,062%Wt), low
nickel and vanadium contents (Ni=1,70ppm, V=trace) suggesting
characteristics of C class (After Barwise, A.J.C, 1984) derived from
lacustrine source rocks.
Results of gas chromatogram of the DST#1 oil from 106-HR-2X
show the presence of saddle shape distribution decreases with
increasing number of carbon atoms (Figure 3.6 and 3.7).
Figure 3.6: C15+ saturates
Figure 3.7: C15+ saturates
chromatogram of oil and
chromatogram of oil and
extracts from 106-HR-1X
extracts from 106-HR-2X
Pristane/phytane ratio is 2,95 and 2,9 for 106-HR-1X ST4, and
106-HR-2X respectively. Consequently, these features are typical of
organic matter derived from a terrestrially dominated source,
deposited in submerged environment under reducing and weak
The GCMS analysis of saturate fraction of crude oil from Ham
Rong field (Figs. 3.8a & 3.9a), the mass fragmentograms of m/z191
shows a wide Hopane distribution, gradually decreased with
reducing number of carbon atoms, which are recognised as organic
matter derived from a terrestrially dominated source, deposited in
reducing environment condition. The presence of Oleanane is land
plant indicators. Distribution of Tricyclic Terpanes sharply
appearence from T2 to T8 suggested lacustrine algae have
contributed in the parent material.
Figure 3.9 Gas
Figure 3.8: Gas chromatography-
Mass Spectrometry (GCMS) of
Spectrometry (GCMS) of
saturates fraction of oil sample from
saturates fraction of oil
sample from 106-HR-2X
The m/z 217 sterane distribution (Figures 3.8b and 3.9b) is
characterised by C29 steranes are higher than those of C27 and C28.
These features suggest the oil derived from terrestrial source. The 4Methyl C30-Sterane (peak 42) widely confirmed as the oil is derived
mainly from lacustrine algal organic matter.
Oil – Source rock correlation defines the origin of oil generated
from lacustrine algal organic matter that match with Oligocene
source rocks in the study area.
3.6. H2S origin in crude oil
Worldwide rift lakes in the Paleocene and Eocene have met in
Spain, southern France, in Utah and Colorado (USA). They formed
in surface of Carbon-Permian or Devon limestone. By this the
carbonate material easily osmoses in the lake that created favorable
condition for carbonate development of along the evaporation zone
The exploration wells in the study area have penetrated thin
limestone in the Oligocene. Theoryly, the H2S and CO2 pollution in
the oil reservoir in the Ham Rong fields were the product of thermal
sulfate reduction process (of CaSO4) in carbonate rocks explained
by Angler-Gofer Scheme formula:
CaSO4 + CH4 = CaS + CO2 + 2H2O
CaS + CO2 + H2O = CaCO3 + H2S
DISTRIBUTION OF SOURCE ROCK AND POTENTIAL
ZONNATION IN THE OFFSHORE NORTHEART SONG
4.1. Oligocene sediment distribution and evolution
On the basis of seismic data and results of latest wells, Phd
student have participated to re-interprete some seismic lines at VPI
workstation. Results of biostratigraphic studies are used to identify
and interprete the seismic reflection surface include:
+ Top Kainozoic basement
+ Top Lower intra- Oligocene (U500)
+ Top of uncomformity is near top of Lower Oligocen (U400)
+ Top Oligocene (U300)
+ Top intra Middle Miocene (U220)
+ Top Upper Miocene (U100)
Some of these seismic horizons just matched tie within a small
area. Oligocene stratigraphic sequence in the center area of block
106 can divide into two parts separated by U400, which is relatively
Eocene?/Oligocen (U500). Well ties to seismic data just observed in
the small troughs in the NE Song Lo fault and the Southern part of
Bach Long Vi Island. The structural maps of Top Basement, Top
U400, Top U300 and the isopach map of Oligocen in scale 1/200.000
The isopach maps of Lower Oligocene (U400-Bsmt) and
Oligocene (U300-Bsmt) (Figures 4.1 and 4.2) represent the
distribution area of Oligocene significant altenated in the offshore
Northeast Song Hong basin. Figure 4.1 shows at the end of Early
Oligocene time, 02 closed lakes systems trending NE-SW and NWSE were developed in the study area. The basement hosts within
Ham Rong field area as boundary separate the lakes. In the Northern
part of block 107, which is belong to South Bach Long Vi trough
also has a deep lake. The lakes in Southeast edge of block 106 and
North of block 107 tend to be open to the Southeast, while the closed
lakes within the Northwest of blocks 102-106 and Northeast Yen Tu
host remain stable development.
Three (03) geological and physical seismic sections were selected
cut through the main structural zonations in the study area to