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Facies analysis with merged 3D seismic data Laisheng Cao
1, 2* , Yingxin Xu
2 , Jingbo Yu
2
1. China University of Geosciences (Beijing) 2. BGP, CNPC
Summary˖
This paper mainly discusses the seismic facies analysis to
the sand bodies of Qing3 group in the south of Songliao
basin with merged 3D seismic data and key wells. The
procedure for basin-fill analysis includes the correlation
between synthetic seismograms and the horizons for
identifying sands, the comparison between 2D section and
3D overlapped section in the same location, two steps FK
filtering, scanning seismic coherency cube, and time-slices
to identify the seismic footprint effects. Consequently, theseismic attributes analysis and waveform clustering
confirm the micro-facies (depositional characteristics). The
result indicates the sands are located in front of the
constructive braided delta, which includes inner part
(dominantly deposits long distant channel sands) and outer
ones (river mouth bars and wedge sands). The traps in the
inner front part are structurally controlled, and the traps in
the outer front are stratigraphic in features.
Key words:3D seismic, acquisition footprint, coherency
cube, waveform clustering, micro-facies, reservoir
conditions
Introduction:
The study area is located in the transitional area from the
west slope to the central depression structurally, the south
of Songliao basin, where is just the front of the joint belt of
four drainage system geographically. Plenty of oil bearing
sequences of Cretaceous are discovered. The exploration
wells indicate existence of thick sands in the middle of the
QingShankou formation with good reservoirs conditions
and high production of oil.
Although the structure description and reservoir prediction
with 2D and limited 3D seismic data have been done for
many times in recent years, the depositional environment
and sequences, sediment source, and lithofacies in the
basin are still fuzzy. Since 2000 Oil Company has acquired
seven blocks of 3D seismic data with the total area
2500Km2 to enhance the prospecting of stratigraphic
reservoirs (Figure 1).
Identification of seismic footprint:
The sand bodies appear as strong reflection event in
seismic section and long abnormal belts on the map of
horizon attributes analysis. Some belts parallel
approximately to the inline direction (NWW), which
almost crosses the whole study area. Does this abnormal
amplitude belts have any geological meaning? Are these
events the footprint of seismic data acquisition?
Figure 1 Horizon amplitude map of Qing 3 group
The footprint of acquisition is mainly caused by the
difference of the bin attributes such as fold, offset
distribution, and azimuth distribution. We correlate the 2D
and 3D sections acquired at the overlapped locations(NNE)
to identify these abnormal reflections. The result of
correlation shows similar strong and discontinuous
reflections in 2D and 3D seismic sections (Figure 2).
In addition, the footprints are the thin “lines” parallel to
the in-line direction or in the form of reticulation on the
slice of coherency cube, hence the cube was used to
identify footprint. We determine that the reflection on the
figure 2 is not a footprint, but as effective event with the
characteristics of stripped horizon amplitude and irregular
geometrical patterns, some parallel to the in-line and some
slanted with the in-line.
Someone may consider the event is caused static
corrections in data processing, but in view of the
topography and near-surface investigation, the drainage
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Facies Analysis with merged 3D seismic data
systems extend in SN direction, which is different from
NWW direction of the target reflections. So, the abnormal
belts are not related with static correction.
Figure 2 Comparison of 2D and 3D seismic section at same
location (crossline direction)
The method to eliminate the footprint is two-step FK
filtering to the migrated 3D data in two directions. No
obvious differences are found in the coherency cube after
filtering, but we can discover the regular subtle changes of
the reflection sequences in space in the target beds.
Maybe someone thinks that the discontinuous points of
strong events are the effects of faults, actually, it is due to
the depositional environment based on the observation to
the coherency cube and horizon time slices on which the
direction of faults is NW, the direction of the effectivereflections is NWW.
Same phenomenon occurs in block 3, 4, and 5 . the upper
sand layers of Qing 3 segment are strong strip like
reflection pattern oriented northwest direction
corresponding to the merged survey(Figure 3).
Figure 3 Amplitude analysis of Qing 3 upper group in block 3,4
and 5
The application of these methods indicates that the event is
not related to the footprint and further research validates
this idea.
Figure 4 Horizon slice of Quantou formation, block 2. Notice
several meandering streams from south to north
Facies analysis:
With the interpretation of seven blocks, the transitional
process from the fluvial facies of Quantou formation
(Figure 4) to the delta of Qingshankou formation is
discovered, the main depositional sources changed from
the south for Quantou formation to the southwest for Qing
2, and the southwest sources for lower Qing 3(Figure 1) to
the west direction for middle Qing 3 and the northwest
sources for upper Qing 3 (Figure 3) .
Before using 3D seismic data to do the research on
reservoir characterization, the top of the thick sands was
treated as a reference plane, and all the sands were
calibrated as the upper Qing 2 group based on the well-tie
section, then the sands would be attributed to as the river
mouth bar sands deposited around the whole southern part
of the depression without any trace of the channels (Figure
5).
There are two wrong ideas. First, simply using the
negative rhythms of the electrical characteristics of the
logs to define the river mouth bars may not be proper
because the bars are closely connected with channels
which frequently changed their ways. The point is that the
positive rhythm appears on one overbank bar of the
channel, and negative rhythm should appear on the other
side alone a single laterally migrated channel. Secondly,
(more critical), the thick sand body may be deposited in
different cycles, and picking the thick sands as a reference
layer may cause time conflict. So, using a single well to
analyze the depositional rhythm may give the complete
wrong result.
2D 3D
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Facies Analysis with merged 3D seismic data
Prior to depositional facies analysis, the top and bottom of
thick sands should be identified by precise calibration of
horizons and interpretation to flattened horizons. It
demonstrates the importance of 3D seismic data in
representing plane changes of depositional facies belts.
The source of objective formation of Qing 3 group, which
is in delta front, is from the southwest Tongyu drainage
system
Figure 5 Correlation between well #17 and #11 in block 1. upper
left is synthetic seismogram of #17, lower #11, and the middle
serigraphic correlations wells. Notice the difference between
before correlations and after. Lower right is depositional facies
based on individual well zonation before seismogram, and upper
is the seismic section with wells and enlarged individual well
section, in which green horizon is top of ē sand and blue bottom
of Ĕ sand.
The sand in well #11 and well #17 were considered as a
same sand formation originally, the correlation of seismic
section with the wells indicates that their features are
totally different. Well #17 shows quantity of sand in ē
formation is more thanĔ, in contract, well #11 quantity in
ē less than Ĕ although the distance between the two
wells is only 3000 meters (Figure 5).
Cube analysis above Qing3 bottom illustrates the typical
channel migration in lateral direction; amplitude in lower
formation slice is stronger in the south than in the north,
but the amplitude in upper formation performances very
different, stronger in the north than in the south.
The target formation Qing3 is located at the front of
braided delta, the depositional source mainly comes from
the southwestern Tongyu river system. Since the
paleotopography of Songliao basin was comparatively flat,
and the project area is situated at transitional zone between
the west slope and central depression of the basin, hence
the straight channels could develop easily and current
migrated with sands, which can be seen in the seismic
cube in the long straight belts with high amplitudes.
By means of waveform clustering with depositional
environment palaeogeomorphology and single well
analysis, mircofacies of Qing 3Ĕ andē are conformed.
During the time the sand Ĕ deposited (Figure 6), the
major channels developed in the southern part, the river
mouth bar, distal bar, and sand sheet were developed in the
northern part. During the time the sand ē deposited
(Figure 7), the subaqueous abandoned channel was in the
southern part, the branch channel and the river mouth bar
were developed in northern part. The channel was moved
from south to north and vertically overlapped several times.
The front of sand Ĕ is in block 1; the sand ē located at
the external front of the delta is out of block 7, these
represent the features of constructive delta.
Figure 6 Micro-facies of sand inĔ block 1
Figure 7 Microfacies of sand inē block 1
Study of reservoir conditions:
The result of depositional facies analysis indicates that
lower Qing 3 in block 1 and 2 located in subaqueous inter
channels, river mouth bar of delta front sheet sands in
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Facies Analysis with merged 3D seismic data
block 3,4 and 5, and front delta in the east of block 6 and
7.
Reservoir conditions change with facies belts. For instance,
the structures is the key factor in block 1 and 2, where the
production wells in the sand formation are located in the
favorable structure position with the thick overlying
shale(Well #17), while well #11 is the dry well due to its
unfavorable structural position. Thin sand and moderate
sand to shale ratio in block 3,4 and 5 provide the
conditions to build up large stratigraphic reservoirs. Up to
now, the reserve, for about 50 million tons, has been
proved.
Conclusions:
1. The strong reflection belts with a strong amplitude
on the seismic sections in our study area, are the
responses from the thick sands, not the seismicfootprint. It is a newly discovered depositional
phenomenon.
2. The target formation Qing 3 sand is located in a
braided delta front; the source of the deposits is from
the southwestern Tongyu drainage system. The
main channel changed from south to north, and the
progradational sands characterized by the
constructive delta.
3. Such depositional feature of these sands occurs also
in the South of Songliao basin. This paper can
provide a referenced method to the analysis of
microfacies using 3D seismic data with high lateral
resolution.
Acknowledgements:
The authors are grateful to Dr. Ling Yun from BGP, and
Mr. Kang WeiLi from Jiling oil field of PetroChina for
their advice and support. And many thanks to Prof. Chen
KaiYuan from China University of Geosciences (Beijing),
Prof. Yuan BingHeng, Prof. Zhang YanQing from BGP.
References:
Cao Laisheng, et al. Study on a special sedimentary
phenomena, 805-809, Expanded Abstracts CPS/SEG 2004
International Geophysics Conference
Cao Laisheng, et al. The technical effect of raising resolution
of 3D seismic exploration in area of South Songliao basin,
1165-1168, Expanded Abstracts CPS/SEG 2004 International
Geophysics Conference
Ling Yun researcher group, Application of basic seismic
attributes to interpretation of depositional environment.
Petroleum Geophysics, 2003, 38(6), 642-653
Yu Shoupeng. High resolution seismic prospecting.
Petroleum press, 1993
Niu Yuquan, et al. New technology Series of geophysics in
oil prospecting. Petroleum press, 1996
Wang Yongchun. Generations and distribution of lithology
reservoirs in south of Songliao basin. Petroleum press, 2001
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EDITED REFERENCES
Note: This reference list is a copy-edited version of the reference list submitted by the
author. Reference lists for the 2005 SEG Technical Program Expanded Abstracts have
been copy edited so that references provided with the online metadata for each paper will
achieve a high degree of linking to cited sources that appear on the Web.
Facies analysis with merged 3D seismic data
References
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Laisheng, C., et al., 2004, The technical effect of raising resolution of 3D seismicexploration in area of South Songliao basin: International Geophysics Conference,
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Ling, Y. researcher group, 2003, Application of basic seismic attributes to interpretationof depositional environment: Petroleum Geophysics, 38, 642-653.
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