Facies Analysis With Merged 3D Seismic Data

7/30/2019 Facies Analysis With Merged 3D Seismic Data

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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

ķ

ĸ

Ĺ

ĺ

Ļ

ļ

Ľ

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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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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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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

Laisheng, C., et al., 2004, Study on a special sedimentary phenomena: International

Geophysics Conference, CPS/SEG, Expanded Abstracts, 805-809.

Laisheng, C., et al., 2004, The technical effect of raising resolution of 3D seismicexploration in area of South Songliao basin: International Geophysics Conference,

CPS/SEG, Expanded Abstracts, 1165-1168.

Ling, Y. researcher group, 2003, Application of basic seismic attributes to interpretationof depositional environment: Petroleum Geophysics, 38, 642-653.

Yu, S., 1993, High resolution seismic prospecting: Petroleum press.Yuquan, N., et al., 1996, New technology Series of geophysics in oil prospecting:

Petroleum press.Wang, Y., 2001, Generations and distribution of lithology reservoirs in south of Songliao

basin: Petroleum press.

Documents

Facies Analysis With Merged 3D Seismic Data