Sedimentary characteristics and hydrocarbon
accumulation of glutenite in the fourth member
of Eogene Shahejie Formation in Shengtuo area
of Bohai Bay Basin, East China
by
Hui Liu, Zaixing Jiang, Yingchang Cao and Yanzhong Wang
reprinted from
ENERGY
EXPLORATION
&
EXPLOITATION
Volume 28 2010
Number 4
©2010
MULTI-SCIENCE PUBLISHING CO. LTD.
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ENERGY EXPLORATION & EXPLOITATION · Volume 28 · Number 4 · 2010
pp. 223-238
223
Sedimentary characteristics and hydrocarbon
accumulation of glutenite in the fourth member
of Eogene Shahejie Formation in Shengtuo area
of Bohai Bay Basin, East China
Hui Liu1*, Zaixing Jiang1, Yingchang Cao2 and Yanzhong Wang2
1
State key laboratory of geological processes and mineral resources, School of Energy
Resource, China University of Geosciences (Beijing), Beijing 100083, China
2
College of Geo-Resources and Information, China University of Petroleum (East China),
Dongying, Shandong 257061, China
*Author for corresponding. E-mail: lhpplu@yahoo.com.cn
(Received 24 May 2010; accepted 7 July 2010)
Abstract
The genetic type and hydrocarbon accumulation conditions of glutenite in
Shengtuo Area have been studied based on cores, well-logs, and formation test
data. During deposition of the fourth member of Eogene Shahejie Formation
(Es4), Shengtuo Area was predominated by nearshore subaqueous fan and
sublacustrine fan, controlled by the Chennan Fault and the Tuo-Sheng-Yong
Fault. Nearshore subaqueous fan and sublacustrine fan were respectively
developed on the downthrown of the Chennan Fault and the Tuo-Sheng-Yong
Fault. Both of nearshore subaqueous fan and sublacustrine fan can be
subdivided into three subfacies, including inner fan, middle fan and outer fan,
from proximal to distal provenance. The braided channel within the middle fan,
characterized by conglomeratic sandstones and sandstones with high secondary
porosity and overpressured microfissures resulted from the effect of organic
acid and reservoir overpressure, is the best reservoir among these three
subfacies. Inner fan subfacies, consisted of thick-bedded, poorly-sorted and
matrix-supported conglomerates, has low primary and secondary porosity, is the
best sealing among this depositional system. Outer fan sediments, comprised of
thick dark mudstones interbedded with thin sandstones in which overpressured
microfissures developed very well, accounts for the migration pathway for oil
and gas to enter braided channel reservoir from source rocks. In addition, the
glutenite fans were developed near the Lijin Sag and the Minfeng Sag, which
deposited two sets of high quality source rocks (Es4s (upper section of Es4) and
Es4x (lower section of Es4) source rock). With regional cap rock and
appropriate preservation conditions, the different subfacies in glutentite fans
worked together and formed a “self-generation and self-storage” lithostratigraphic trap characterized by “migrating through outer fan, accumulating
in middle fan and sealing by inner fan”.
224
Sedimentary characteristics and hydrocarbon accumulation of glutenite
Keywords: Glutenite reservoir, Nearshore subaqueous fan, Sublacustrine fan,
Shengtuo Area, Bohai Bay Basin
1. INTRODUCTION
Glutenites, especially those block-like massive deposits in rift basins, consist of
sandstones and conglomerates, commonly include alluvial fan, fan delta, nearshore
subaqueous fan and sublacustrine fan (Kong, 2000; Sui, 2003). These fans are
generally developed during the late stage of initial subsidence and the early stage of
accelerated subsidence (Wu et al., 2002), and formed on the escarpment of rift basins
characterized by steep slope, proximal provenance, high relief topography and intense
tectonic movement (Kneller and Branney, 1998; Dasgupta, 2002; Han et al., 2003;
Lin et al., 2005). These glutenites interfingering with lacustrine mudstones and being
near source rocks, can form multi-type reservoirs (Xie et al., 2002; Zouhri, 2004).
As the development of the major oil and gas bearing basins has been deeply
maturated in China, the focus of the onshore exploration objectives have turned to the
litho-stratigraphic reservoirs (Jia and Chi, 2004; Jia et al., 2004; Jia et al., 2008; Sun
et al., 2009). As an important type of litho-stratigraphic reservoirs, the exploration of
glutenite reservoirs has made a great breakthrough in rift basins like Nanxiang Basin
and Bohai Bay Basin in Eastern China recently (Jiang et al., 2003). For example,
glutenite reservoirs with an approximate amount of 6 108 t account on 7.63% of the
proven oil reserves in Bohai Bay Basin (Yuan and Qiao, 2002). The glutenite
reservoirs have become key litho-stratigraphic reservoirs in rift basins of Eastern China
(Sun, 2003; Lin et al., 2005; Qi, 2006).
Shengtuo Area is located on the northern escarpment of Dongying Depression in the
Bohai Bay Basin (Fig. 1). Due to steep topography, proximal provenance, and intense
structural activities (Yuan and Xu, 2003; Yan et al., 2005), the glutenites fans,
including nearshore subaqueous fans and sublacustrine fans, developed widely in this
area during deposition of the fourth member of Eogene Shahejie formation (Es4),
(Jiang et al., 2003; Sun, 2003). These glutenite fans have become important
exploration targets in the Dongying Depression currently. For example, the formation
test data indicated that Well FS1 produced 81.7 t/d of oil and 11.8 104 m3/d of gas
in braided channel sand bodies of nearshore subaqueous fan, and Well T764 produced
15.21 t/d of oil and 1043 m3/d of gas in braided channel sand bodies of sublacustrine
fan. However, due to the lacks of understanding of high-quality reservoir distribution
and hydrocarbon accumulation patterns of glutenite, success rate of glutenite reservoir
exploration is relatively low. At present, success rate of exploration well with over 5 t/d
oil production is about only 10%. So, detail studying of sedimentary characteristics and
hydrocarbon accumulation patterns of glutenite reservoirs in Shentuo Area is very
important to increase the sucess rate of exploration of glutenite reservoir on the steep
slope of fault basin or rift basins.
2. GEOLOGIC BACKGROUND
Dongying Depression is located on the southeast of Bohai Bay Basin, with escarpment
structural belt controlled by the shovel-shaped Chennan Fault in north. Shengtuo Area
ENERGY EXPLORATION & EXPLOITATION · Volume 28 · Number 4 · 2010
225
is located in the center of the escarpment structural belt, with Chenjiazhuang Bulge in
north, Central Fault anticlinal zone in south, Lijin Sag in the southwest, and Minfeng
Sag in southeast (Fig. 1). The exploration area of Shengtuo Area is about 230 km2
(Zhang et al., 2004; Sun, 2006) (Fig. 1). Since 1960’s, seven oil-bearing strata have
been discovered, including the fourth (Es4), the third (Es3), the second (Es2) and the
first member (Es1) of Shahejie Formation, Dongying Formation (Ed), Guantao
Formation (Ng) and Minghuazhen Formation (Nm) with total estimated oil reserves of
over 5 108 t (Li et al., 2003). The discordogenic faults, such as Chennan Fault and
Tuo-Sheng-Yong Fault together with their descendent faults in the central and northern
part of Dongying Depression, controlled the development of the deposition of
Shengtuo Area (Ren et al., 2004; Zhu et al., 2004). The study interval Es4 is in the
early stage of the second chasmic stage of Dongying Depression (Yuan and Xu, 2003).
The climate was semiarid and muggy during Es4 (Wang et al., 1994; Sun, 2006) and
it was in favour of mechanical weathering of mother rock and development of glutenite
sediments. On the setting of the steep topography controlled by Chennan Fault and
Tuo-Sheng-Yong Fault, gravity flows caused by surging flood, formed nearshore
subaqueous fan and sublacustrine fan, which were closed to the source rock in the
center of the Dongying Depression (Kong, 2000; Wang and Sui, 2003; Yan et al.,
2005).
Figure 1. (A) Location of Shengtuo Area in Dongying Depression of Bohai Bay
Basin. (B) Structure map of Shengtuo Area. CN Fault-Chennan Fault;
TSY Fault-Tuo-Sheng-Yong Fualt.
3. FACIES ASSOCIATIONS
Based on a comprehensive analysis, it concluded that the glutenites of Es4 in Shengtuo
Area were primarily developed in two major sedimentary facies, nearshore subaqueous
fan and sublacustrine fan. Nearshore subaqueous fan was developed on the
downthrown of Chennan Fault being closed to the provenance, whereas sublacustrine
fan was deposited on the downthrown of Tuo-Sheng-Yong Fault being far away from
the provenance (Fig. 2).
226
Sedimentary characteristics and hydrocarbon accumulation of glutenite
az
gB
u lg e
NE
ji
en
Ch
an
hu
CN
t
l
Fau
Sublacustrine Fan
t
Nearshore
Subaqueous Fan
aul
YF
Fault
TS
Bulge
Figure 2. Depositional model of glutenite in Es4, Shengtuo Area. CN Fault-Chennan
Fault; TSY Fault-Tuo-Sheng-Yong Fualt. Nearshore subaqueous fan was developed
on the downthrown of Chennan Fault being closed to the provenance, whereas
sublacustrine fan was deposited on the downthrown of Tuo-Sheng-Yong Fault being
far away from the provenance.
3.1. Nearshore subaqueous fan
During Es4, nearshore subaqueous fans spread widely on the downthrown of Chennan
Fault. The Nearshore subaqueous fan is mainly composed of matrix-supported
conglomerates. The gravel is poorly-sorted and poorly-rounded, showing angular or
subangular shape. Multiple phase fans are separated by dark mudstones, and single fan
can be divided into inner, middle and outer fans from near source to distant source (Fig.
3a, Jiang, 2003).
Inner fan is dominated by main channel, which is characterized by matrix-supported
conglomerates (Fig. 4A), grain-supported conglomerates (Fig. 4B), pebbled sandstones
with dark mudstones. Matrix-supported conglomerates display boulder-like structure
and mussily even vertically distributing of gravel. The bottom scour structures
are well developed in the main channel, whereas bedding or laminate structures are
poorly developed. Middle fan is composed of braided channel sand bodies, which is
the main component of nearshore subaqueous fan. The braided channel is mainly
ENERGY EXPLORATION & EXPLOITATION · Volume 28 · Number 4 · 2010
227
comprised of pebbled coarse-grained sandstones, medium-grained sandstones, and a
few conglomerates. Compared to the main channel, braided channel has fewer
conglomerates and more sandstones. Various sedimentary structures are well developed
and observed in the braided channel, such as scour surfaces, graded beddings and parallel
beddings (Fig. 4C, D). In vertical section, braided channels present as multiple-phase
sandstone beds superimposing together without mudstone interlayers. Outer fan is
characterized by thick dark mudstones interbedded with thin siltstones and silt-finegrained sandstones. Sedimentary structures in the outer fan include deformed structures
such as ball-and-pillow structures, load cast (Fig. 4E), and sandstone dike structures. In
vertical section, inner fan, middle fan and outer fan successively develop from bottom to
top, showing a fining-upward sequence (Fig. 3a).
Stratum Depth
Facies Sequence
(m)
70
forma
system -tion member
SP
(mv)
95
Porosity
(%)
1200
10
20
Horizontal
Permeability
(10 um
−3
Facies
2
subfa micro
300.011 100 10000 -cies facies
Well
Stratum Depth
Facies Sequence
(m)
2
forma
system -tion member
Sp
(mv)
Porosity
(%)
30
10
Horizontal
Permeability
(10 um
−3
Facies
2
subfa micro
300.011 100 10000 -cies facies
Well
fan
3023
20
3837
fan
3024
3838
3025
outer
3956
fan
fan
3097
3840
3957
channel
3027
member
Formation
outer
3839
channel
member
Formation
3026
T764
3958
middle
3959
3960
braided
T168
middle
3100
braided
3099
Eogene
Eogene
3098
3961
3962
40
80
fan
channel
inner
3534
feeder
fan
3488
channel
3487
4th
Shahejie
4th
Shahejie
3101
3489
3535
T720
main
inner
3490
3491
3536
3492
3537
a nearshore subaqueous fan
gravel
b sublacustrine fan
sand
mud
sandstone dike
Figure 3. Facies sequence and physical properties of nearshore subaqueous fan and
sublacustrine fan. See Figure 1 for well locations. Both of nearshore subaqueous fan
and sublacustrine fan, inner fan, middle fan and outer fan successively develop from
bottom to top, showing a fining-upward sequence in vertical section. The braided
channel within the middle fan, characterized by conglomeratic sandstones and
sandstones with high porosity and permeability, is the best reservoir among these
three subfacies.
3.2. Sublacustrine fan
The concept of sublacustrine fan derived from submarine fan (Stow et al., 1984;
Shanmugam and Moiola, 1988; Payros and Pujalte, 2008). In lacustrine basin, it
228
Sedimentary characteristics and hydrocarbon accumulation of glutenite
generally refers to the flood gravity flow fan with longer feeder channel (Prabir, 2002;
Jiang, 2003). During Es4, sublacustrine fans mainly distribute on the downthrown of
Tuo-Sheng-Yong Fault. Same as nearshore subaqueous fan, sublacustrine fan could be
subdivided into inner, middle and outer fans (Fig. 3b).
Inner fan is dominated by feeder channel, which is comprised of matrix-supported
conglomerates (Fig. 4F), grain-supported conglomerates and pebbled sandstones. The
massive conglomerates are poorly-sorted and poorly-rounded. Middle fan, the main
part of sublacustrine fan, is characterized by braided channel, which is consisted of
conglomerates, pebbled sandstones, and sandstones with thin-beded mudstones. The
sediments within a single sequence from the bottom to the top are conglomerates,
pebbled sandstones, and sandstones (Fig. 4G), which reflect a gradual change from
gravel to sandy high density turbidity. Graded bedding (Fig. 4G), mud chippings
(Fig. 4H) and scour structure (Fig. 4I) are very common in braided channel. Incomplete
Bouma sequence, ripple bedding, and contemporaneous deformation structures (Fig.
4J) are the common sedimentary structures in fine-grained sediments between braided
channels, whereas large-scale cross bedding is rare. Outer fan consists of mudstones
with thin-beded siltstones and fine sandstones showing characteristics of C, D and E
sections of Bouma sequence. Parallel bedding is the main sedimentary structure in the
argillaceous sediments.
Figure 4. Core photos showing different sedimentary structures in glutenite in Es4,
Shengtuo Area. (A) Matrix-supported conglomerates, from well T165 at 3498.8 m.
(B) Grain-supported conglomerates showing graded bedding, from well T166 at
3464.1 m. (C) Scour surfaces, from well T134 at 3197.58 m. (D) Graded beddings
(down) and parallel beddings (up), from well T127 at 2826.43 m. (E) Load cast, from
well T165 at 3219.9 m. (F) Matrix-supported conglomerates, from well T720 at
3673.3 m. (G) Graded beddings, from well T153 at 3546.9 m. (H) Mud chippings,
from well T710 at 3604.5 m. (I) Scour surfaces, from well T762 at 3265.8 m.
(J) Load cast and sandstone ball, from well T762 at 3493.9 m. Photos from A to E
belong to nearshore subaqueous fan, and photos from F to J belong to sublacustrine
fan. The diameter of core is 10 cm. See Figure 1 for well locations.
ENERGY EXPLORATION & EXPLOITATION · Volume 28 · Number 4 · 2010
229
4. HYDROCARBON ACCUMULATION ELEMENTS AND MODEL
4.1. Source rock
Timing of source rock mature and expulsion is an important factor that controls the
distribution of oil and gas (Magoon and Dow, 1994; Sun and Liu, 2009). Shengtuo
Area has superior source rocks, as a result of being close to Lijin and Minfeng oilgeneration sags where two sets of high quality source rocks developed during Es4s and
Es4x (upper section and lower section of Es4) (Table 1).
Table 1. Parameters of source rock in Lijin and Minfeng sags.
Format- ThickTOC
Chloroform
ion
ness(m)
(%)
bitumen “A”(%)
Ro
S1(mg/g)
Es4s
50 ~ 150 0.6 ~ 8.2
0.3 ~ 0.8
0.45~0.93
Es4x
200
0.12 ~ 4.1 0.104 ~ 1.127 0.93~1.25 0.02~8.24
S2(mg/g) Kerogen
I,II1
0.03~7.19
II
The lithology of source rock of Es4s consists of mainly dark-gray mudstone and
calcareous mudstone with oil shale, which developed in semi-deep to deep lake with semisaline to saline water (Zhang et al., 2009). The source rock was characterized by higher
accumulation thickness (50~150 m) and organic matter abundance (TOC: 0.6~8.2%,
generally more than 2%; content of chloroform bitumen “A”: 0.3~0.8%, generally more
than 0.6%). The kerogen is dominated by type I and type II1, and Ro is between 0.45 and
0.93. In sum, the source rock of Es4s is a set of excellent quality source rock.
The source rock of Es4x occurs between and below the gypsolyte-salt rock layers,
and the accumulation thickness is about 200 m. TOC is 0.12~4.1%, generally more
than 0.5%. Content of chloroform bitumen “A” is 0.1041%~1.127%. Potential
hydrocarbon S1 is 0.02~8.24 mg/g, and S2 is 0.03~7.19 mg/g. Organic matter is mainly
terrigenous high grade plant and low grade aquatic organism in the semi-saline to
saline water. The kerogen is dominated by type II and few type I. Ro is between 0.93
and 1.25. From the top to the bottom of Es4x, the maturity of organic matter is from
mature to highly mature. Source rocks of Es4x generated oil condensate in mature
phase and gas in highly mature phase (Wang, 2009).
4.2. Reservoir
Due to the difference in hydrodynamic force, location and diagenesis, the different
subfacies of glutenite fans have different physical properties. Physical properties of
inner and outer fan are relatively poor, with porosity being less than 5% and
permeability being less than 1 md in general. Physical properties of braided channel
in middle fan are much better, with porosity being between 10% and 25% and
permeability being between 100 md and 1000 md (Fig. 3). Braided channel can be the
reservoir for hydrocarbon accumulation. Several elements are responsible for braided
channels to be favorable reservoirs. (1) The braided channel is mainly composed of
pebbly sandstones, gritstones with superimposed scour structure and classic turbidites.
Grain-supported glutenite has the characteristics of less matrix, moderate gradation and
medium thickness. Consequently, the original physical property of braided channel is
relatively good. (2) A lot of secondary pores (Fig. 5) can be produced when a large
230
Sedimentary characteristics and hydrocarbon accumulation of glutenite
amount of organic acid generated and the acid got into braided channel glutenite in the
process of organic material thermal evolution (Schmid and Mcdonald, 1979; Surdam,
1989; Meng et al., 2008). (3) Formation overpressure exiting widely in the Es4 of
Shengtuo Area (Liu et al., 2009), which inhibited compaction and cementation, made
reservoir spaces of braided channel preserve well (Wilkinson et al., 1997; Holm, 1998;
Osborne and Swarbrick, 1999; Gao and Zhang, 2001; Chen et al., 2002). In addition,
formation overpressure also made glutenite form a series of overpressured fractures
(Fig. 5), which increased the permeability of glutenite greatly.
Figure 5. Reservoir space types of braided channel within the middle fan of glutenite
in Es4, Shengtuo Area. (A) Dissolved pore of matrix (100/-), from well T764 at
3956.10 m. (B) Intragranular dissolved pore (100/-), from well T720 at 3672.60 m.
(C) Carbonate cement dissolution (100/-), from well T720 at 3673.00 m. (D)
Structural fracture (40/-), from well T79 at 3407.41 m. (E) Over-pressured fracture
(100/-), from well T719 at 3562.30 m. (F) Shrinkage joint (40/-), from well T166
at 3253.8 m. See Figure 1 for well locations.
4.3. Petroleum migration
The glutenites of nearshore subaqueous fan and sublacustrine fan of Es4 in Shengtuo
Area are close to the source sags. The main migration style of hydrocarbon is episodic
flow through the overpressured micro-fracture system. Due to uncompaction and
generation of hydrocarbon, the pore fluid pressure of source rock increases gradually
(Bradley, 1975; Sahay and Fertl, 1988; Cobbold et al., 2004). When the pressure
exceeds formation breakdown pressure, the overpressured micro-fissures form, and the
hydrocarbon and other fluid discharge along the micro-fissures by the way of flashy
flow (Ghaith et al., 1990; Hunt, 1990; Ortoleva, 1994; Roberts and Nunn, 1995). With
the discharging of fluid, the pore fluid pressure decreases to the level below the
formation breakdown pressure, and micro-fissures are closed and overpressured fluid
stops discharging (Cha et al., 2002; Gao et al., 2009). Based on the analysis of cores,
ENERGY EXPLORATION & EXPLOITATION · Volume 28 · Number 4 · 2010
231
vertical mineral vein developes very well in the contact zone of mudstones and
sandstones in overpressured zone. The deeper the depth is, the more the vein
developes. It has been proved that flowing of micro-fissure is very common in
overpressured zones (Liu and Xie, 2003). A mass of overpressured micro-fissures are
found in the source rocks of Es4 in study area, for example, in dark mudstones,
calcareous mudstones and thin-bedded sandstones in Well Li88 (Fig. 6A). Most of the
fissures are filled with calcite, whereas crude oil is found in parts of open fissures in
thin-bedded sandstones (Fig. 6B). These are the evidences of episodic flowing from
source rock to reservoirs.
Figure 6. Overpressured microfissure in cores of out fan in Es4, Shengtuo Area.
(A) Overpressured fracture in mudstone of source rocks, from well L88 at 2985.1 m.
(B) Over-pressured fracture of thin-bed sandstone in outer fan, from well L88 at
2875.9 m. See Figure 1 for well locations.
4.4. Sealing and preservation conditions
A set of 80~200 m thick dark mudstones with calcareous mudstones and thin-bedded
sandstones distribute consistently from the bottom to top of middle section of the Es3
in Dongying Depression. In addition, calcareous mudstones generated “tight shell”
during compaction. The dark mudstone and “tight shell” could serve as favorable
sealing layers (Hu, 1989), forming regional seal of glutenite reservoirs. The inner fan
is mainly consisted of thick-bedded and poorly-sorted matrix-supported conglomerates
interbedded with thin none lacustrine mudstones. Primary pores and secondary pores
were poorly developed in the inner fan due to strong compaction. As a result, the
physical property of inner fan is extremely poor (Fig. 3), so the inner fan can be an
effective lateral seal bed for glutenite reservoirs in braided channel. In the later
structural evolution, Es4 had experienced consistent subsidence in Shengtuo Area, and
few faults were developed in Es4. Consequently, the glutenite reservoirs of Es4 in
Shengtuo Area had been preserved in very good conditions.
4.5. Hydrocarbon accumulation model
Different subfacies act different roles in the hydrocarbon accumulation process of
glutenite fans of Es4 in Shengtuo Area (Fig. 7).
232
Sedimentary characteristics and hydrocarbon accumulation of glutenite
T764
Nearshore
Subaqueous Fan
Sublacustrine Fan
Fault
Gypsolyte
Inner fan
Inner fan
Basement
Dark mudstone
Middle fan
Middle fan
Reservoir
Migration
Direction
Outer fan
Outer fan
Figure 7. Hydrocarbon accumulation model of glutenite in Es4, Shengtuo Area. This
source-reservoir-seal assemblage, hydrocarbon generated by mature source rock got
into braided channel reservoirs of middle fan through overpressured micro-fissures of
outer fan, formed “self-generation and self-storage” lith-stratigraohic trap, which was
characterized by “migrating through outer fan, accumulating in middle fan and
sealing by inner fan”. See Figure 1 for section locations.
Inner fan is composed of thick and poorly-sorted matrix-supported conglomerates
(Fig. 3). Primary pores and secondary pores are dramatically reduced due to the strong
compaction in the inner fan. As the result, inner fan with extremely poor physical
property (Fig. 3) contributes to the lateral seal. In addition, overlain dark mudstone and
“tight shell” in middle section of Es3 could serve as favorable regional seal of glutenite
reservoirs.
Braided channel in middle fan is characterized by pebbly sandstones and sandstones
(Fig. 3) with abundant secondary pores and overpressured micro-fissures (Fig. 5) made
by organic acid and reservoir overpressure. The braided channel with much better
physical property (Fig. 3) could be favorable reservoirs.
Outer fan is comprised of thick-bedded dark mudstones interbedded with thinbedded sandstones (Fig. 3) with overpressured micro-fissures (Fig. 6). Although being
non-effective reservoir, the thin-bedded sandstones in the outer fan could be a good
migration pathway for oil and gas entering into braided channel sand bodies from
synsedimentary source rocks in basin ward direction (Lijin and Minfeng oil-generation
sags (Es4s and Es4x)).
With regional seal and later preservation, the different subfacies worked
together, and formed “self-generation and self-storage” litho-stratigraphic trap,
which was characterized by “migrating through outer fan, accumulating in middle
fan and sealing by inner fan” (Fig. 7). Based on the model of hydrocarbon
accumulation, enhancing the sedimentary study of glutenite and then searching for
the braided channel within middle fan is the effective method of increasing the
sucess rate of exploration of glutenite reservoir on the steep slope of fault basin or
rift basins.
ENERGY EXPLORATION & EXPLOITATION · Volume 28 · Number 4 · 2010
233
5. CONCLUSION
Based on the depositional environment, hydrodynamic force, formation mechanism
and depositional characteristics, the glutenite of Es4 in Shengtuo Area is developed in
nearshore subaqueous fan and sublacustrine fan. Nearshore subaqueous fans were
developed on the downthrown of Chennan Fault, whereas sublacustrine fans
were deposited on the downthrown of Tuo-Sheng-Yong Fault. The inner fan of
glutenite mainly consisted of massive conglomerates supported by matrix. Middle fan,
the main part of glutenite, was characterized by braided channel and consisted of
pebbly coarse sandstones and medium-sandstones. The lithology of outer fan was
mainly dark mudstones with thin-bedded siltstones and fine-grained sandstones.
Glutenite of Es4 in Shengtuo Area have superior oil sources conditions, due to
being close to Lijin and Minfeng sags which have two sets of high quality source rocks.
Gluenites in braided channel of middle fan with abundant secondary pores and
overpressured micro-fissures, have better physical properties, and can be favorable
reservoirs. Dark mudstones and gypsolyte-salt rocks closed to glutenite and inner fan
with extremely poor physical properties can be good seal for glutenite reservoirs. The
thin-bedded sandstones plus a certain of overpressured micro-fissures in the outer fan,
connecting the source rock in the basin ward and the reservoir (middle fan braided
channel) in the coast ward, is the good pathway for oil and gas migration. This sourcereservoir-seal assemblage, hydrocarbon generated by mature source rock got into
braided channel reservoirs of middle fan through overpressured micro-fissures of outer
fan, formed “self-generation and self-storage” lith-stratigraohic trap, which was
characterized by “migrating through outer fan, accumulating in middle fan and sealing
by inner fan” (Fig. 7).
ACKNOWLEDGEMENTS
This work was co-funded by the National Science and Technology Special (Grant
No. 2009ZX05009-002), the Innovative Team Development Plan of the Ministry of
Education of China (Grant No. IRT0864) and the New Century Excellent Researcher
Award Program from Ministry of Education of China (Grant No. NECT-06-0604).
We thank the Geoscience Institute of the Shengli Oilfield, SINOPEC, for the
permission to access their in-house database. Thanks are also extended to Dr. H.B.
Lu of Shell International, Dr. L. Zhang at ConocoPhilips China Inc., Mr. Y. Wang at
the Schlumberger-Beijing GeoScience Center and Dr. W. Dong at Virginia
Polytechnic Institute and State University in USA for polishing the English of the
manuscript.
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