深部矿井地震散射波成像数值模拟(英文)

272

Numerical simulation scattered imaging in deep mines*

Manuscript received by the Editor June 1, 2010; revised manuscript received August 2, 2010.

*This work is supported financially by the National Key Project (Grant No. 2008ZX05035), the 973 Program (Grant No. 2009CB219603 and 2007CB209406), and the National Natural Science Foundation of China (Grant No. 50974081).1. The School of Resource and Earth Science, China University of Mining and Technology, Xuzhou, 221116, China.

2. State Key Laboratory For Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, 221116, China.

3. Key Laboratory of CBM Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou, 221116, China.

APPLIED GEOPHYSICS, Vol.7, No.3 (September 2010), P. 272 - 282, 9 Figures

DOI: 10.1007/s11770-010-0249-2

Hu Ming-Shun 1,2, Pan Dong-Ming 1,2, and Li Juan-Juan 1,3

Abstract : Conventional seismic exploration, mostly based on reflection theory, hardly has accurate imaging results for disaster geologic bodies which have small scale, steep dip, or complex structure. In this paper, we design two typical geologic models for analyzing the characteristics of scattered waves in mines for forward modeling by finite difference and apply the equivalent offset migration (EOM) and EOM-based interference stack migration methods to mine prospecting. We focus on the analysis of scatted imaging’s technological superiority to reflection imaging. Research shows: 1) scattered imaging can improve fold and make the best of weak scattered information, so it shows better results than post-stack migration imaging and 2) it can utilize the diffraction stack migration method-based ray path theory for mine seismic advanced prediction, so it provides an new efficient imaging method for improving resolution of mine seismic exploration.

Keywords : mine; seismic exploration; scattered wave; seismic imaging; numerical simulation

Introductions

Coal resources have gradually come into the deep exploitation stage in China. Geologic problems, gas and water inrush, and so on, affecting mine safety and efficient production become more incisive with deeper exploitation. These problems bring difficulties for making project layout and scientific decisions, especially for deep coal resource exploitation, because of the complexity of deep coal seams and surrounding rocks, difficulties of deep exploration, and less data in deep mines. Ground exploration has quite limited resolution, especially in deep strata (Liu and Li, 1993) and it hardly satisfies the geologic requirements for deep mine

exploitation. So it is necessary to improve exploration precision for small scale structures in deep mines.

There are many mine geophysical prospecting techniques recently, for instance, the seismic reflection wave method, Rayleigh wave exploration, channel wave surveys, direct current, transient electromagnetic, electromagnetic wave penetration, ground penetrating radar (Wu et al., 2005). Electrical prospecting has a volume effect so it is too difficult to accurately detect subtle structures. The seismic elastic wave field has the potential ability to detect subtle structures because it contains abundant information about the media. So the research and development of mine seismic exploration techniques have important significance to improve the detection accuracy of geological structures in deep mines

Hu et al.

(Zhu et al., 2008).

Even now, mine seismic imaging chiefly depends on reflected waves. However, actual mine geological conditions are often quite complex, so the seismic wave field is usually greatly complex with multiple arrivals because of the development of faults and fissures, steep strata dip, lithology alteration, and multi-scale heterogeneous geologic bodies near the mine. Under the circumstances, reflection signals recorded in the coal vein are quite weak and have low SNR and which sometimes even cannot be received. This consequentially influences the imaging (Wu and Aki, 1985a; 1985b; 1993; Aki and Richards, 1986; Liu et al, 2000).

The equivalent offset migration (EOM) method (Bancroft and Geiger, 1994; Bancroft and Li, 1998; Geiger and Bancroft, 1996) was proposed by Bancroft, who is member of CREWES at the University of Calgary. It is a higher efficiency imaging method. Prof. Liu Xue-Wei has studied scattered wave imaging in metal mine prospecting for many years (Wang, 2005; Yin, 2005; Gou, 2007; Li, 2006). Zhang and Liu (2006; 2008) have studied anisotropic converted wave amplitude-preserving prestack time migration by the pseudo-offset method. Zhang et al. (2009) adopted the EOM method to acoustic log reflection imaging. Better imaging results using scattered imaging have been achieved in these fields and the conventional imaging method has improved enormously (Zhang et al., 2009). Based on this, we adopt the scattered imaging method to mine seismic prospecting to improve the imaging results.

Based on real geological conditions in mines, we build two inhomogeneous medium numerical models, analyze the characteristics of scattered wave propagation, extract common scatter point (CSP) gathers and common mid-point (CMP) gathers from forward synthetic shot records, compare the characteristics of scattered waves in CSP and CMP gathers, and test the scattered imaging method. All of this research will provide a theoretical basis for deep mine scatter prospecting.

Theory of scattered waves

Based on the Huygens-Fresnel principle (Aki and Richards, 1986), each point of a wave front at arbitrary time can be regarded as a new point source which can cause secondary disturbances and the disturbances form an elemental wave front. The position of the new wave front is the envelope of every elemental wave front. The new disturbance is formed by the wave front interference stack at the survey point, so some wave energy can always propagate back to the origin even though no reflection wave energy can be received. This is called the back scattered wave (inverse scattering) caused by interaction between the incident wave and an inhomogeneous medium, and which contains inhomogeneity information of the subsurface medium. The formation of reflected and scattered waves is shown in Figure 1.

Scattering

Reflection

Fig. 1 Schematic diagram of re? ected and scattered waves formation mechanism.

To a point in the subsurface, incident and reflected waves have a one-to-one correspondence and incident angle is equivalent to reflection angle. Incident and scattered waves have a one-to-many correspondence as does incident and scattered angles. Reflected waves are generated by a layered homogeneous medium and its changes of travel time and amplitude are caused by a large scale inhomogeneous medium. A reflection wave is the result of the point scattered waves stacking in phase, so we can say it is a special case of a scattered wave. From the physics perspective, there are two cases when an incident wave encounters an rough interface: roughness scale is too small or too large compared with wavelength. The first can cause reflected waves while

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the second causes scattered waves. In the real word, the response of a seismic wave excited by a source generally has three instances: scattering, diffraction, and reflection. Scattering is the most general and the production condition is the most common, diffraction is the second most general, and the production condition of reflections is the strictest and requires a relatively smooth interface. The scattered wave is a concept of full seismic wave field which propagates according to the Huygens-Fresnel principle and the most basic manifestation of scattered waves is single point scattering. Reflection, diffraction, reverse, and direct waves are all the result of the single point scattered interference stack. Because actual geological problems are often very complex for multiple-scale geologic bodies, the seismic wave field is very complex due to multiple wave interference. Therefore, single wave field theory cannot represent a complex seismic wave field and the solution of complex problems should be based on a generalized scattering theory (Yin, 2005). Therefore, the scattered wave exploration technique has widely practical value in complex geological structure or heterogeneous geologic body prospecting.

Methods of scattered imaging

Scattered imaging is a method based on scattered theory and the characteristics of the scattered wave field, which holds that subsurface media are formed by large scattered points. The key step of the method is extraction of common scatter point (CSP) gathers by means of equivalent offset gathers.

Equivalent offset and extraction of CSP gathers Inhomogeneous geological bodies consist of scattering points. Each receiver point will receive every scatter point’s information and the wave field stacks backscattered energy from all scatter points. Figure 2 shows a schematic diagram of a single point model’s propagation path and travel time. The seismic wave travels from source to scatter point and back to all receiver points. All geophones can receive scatter energy. The travel time equation of source–scatter point-receiver is:

,

s r

t t t (1) Assuming that the seismic wave propagation velocity as a constant v, equation (1) can be extended to a double square root equation (DSR):

11

22

22

22

00

22

,

z x h z x h

t

aoao

????

????

????

(2)

where z0 is the scattered point depth, x is the distance from source-receiver CMP to the scatter projection (SP), and h the half offset. Actual seismic propagation velocity is varying so the double square root equation (2) can also be written:

11

22

22

00

22

-

, 22

mig mig

x h x h

t t

t

v v

aoao

§·§·

????

¨?¨?

?1?1

????

????

(3)

where x is distance from scatter projection to CMP, h the half offset, t0 is the zero offset two-way travel time, t is the seismic wave travel time, and v mig is the root-mean-square velocity at t0.

x

propagation path.

SP is the surface projection of the subsurface scattered point, MP

is the mid point between source and receiver, h the half offset,

x-the distance from scatter projection to mid point (MP), R-the

receiving point, S-the source, t s is the travel time from source

point to scatter point, and t r is the travel time from scatter point to

receiving point.

In Figure 3, we put the shot and receiving point at the same position (point E) and make the travel time of seismic wave from equivalent shot point (E) to scattering point (SP) and then to equivalent receiver point (E) equal to the travel time of seismic wave from shot point (S) to scattering point (SP) and then receiving point (R): t= 2t e= t s+t r. The distance from point E to the

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surface projection of the scattering point is defined as the equivalent offset, expressed by h e . Equation (4) is proposed as:

1

2

22

0222.2e e mig t h t t v ao

§· ??¨??1????

(4)

From equation (3) and equation (4), we have

1112

22

222

2

2

2

00022

2-2.222e mig

mig mig x h x h t h t t v v v aoaoao

§·§·§· ??????¨?¨?¨??1?1?1?????????

???

11

1222

222

2

22

00022

2-.222e mig mig mig x h x h t h t t v v v aoaoo

·§·§· ??????¨?¨?1?1?1??????????

(5)After simplifying equation (5),

2

2222.e mig xh h x h tv §·

¨?¨??1

(6)

So the double square root (DSR) of equation (3) can be transformed into a single square root equation (6), which is a transform from a shot gather input to a

CSP gather. Only by the equivalent offset method can we transform all data into CSP gathers with no time shift, although the DSR equation can be converted into different single square root equations as shown by Fowler (1997). The CSP gather is equal to a zero-offset time section. Based on the equivalent offset principle, a CSP gather is equivalent to a common depth gather (CDP) for every point but a CMP gather is not and only when the seismic wave encounters a horizontal reflector (Bancroft and Geiger, 1994). Therefore, scattering

imaging is theoretically more adaptive.EOM imaging method From equation (6) we see that the time-distance curve of the scattered wave is a hyperbola, so scattered wave imaging can be performed by the Kirchhoff integral. This method is Kirchhoff integral scattered wave imaging and we call it the EOM imaging method (Bancroft et al., 1998).

Method of interference stacked scattering imaging

A CSP gather has plenty of traces and fold because all traces will be used when extracting the CSP gather. The CSP gather for each point is a zero-offset time section. The scattering energy expression for each point is a hyperbola and the hyperbola vertex is at the trace whose equivalent offset is zero. Scattering energy from different gathers but the same position can be stacked to give a high SNR zero-offset section by the interference stack principle. After that, migration is necessary. The final result is called the interference stack migration section. This is the principle of interference stack scattered imaging (Gou, 2007).

Numerical simulations

Model of lower group coal containing collapse column

Model parameters and geometry

For the purpose of mine construction design and exploitation safety, we must make the occurrence of the coal seam and geological structure clear before the lower group coal exploration with conditions of karst-cranny development, small-sized buried collapse columns, and fault spatial distribution and throw. However, subtle deep records cannot be obtained for ground surveys because of rock mass failure caused by the upper group coal exploitation and a large amount of coal mining

Fig. 3 Diagrammatic sketch of equivalent offset de? nition.

CSP is the projection of the scatter point at the surface, h e is the equivalent offset, R is the receiver point, S is the shot point, E is the equivalent coincident shot and receiver point, CMP is the common mid point, t e is the travel time from point E to the scatter point, t s is the travel time from the shot point to scatter point.

CMP R

S

CSP

Scatter point

t 0/2 or z 0

t /2

2t e

h e

E

Hyperbola

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Numerical simulation scattered imaging

waste material. So, during upper group coal exploitation, detecting the lower group coal at a short distance provides a reliable geological basis for the lower group coal exploration over a limited area. A model of the lower group coal containing a collapse column is built to study scattered imaging (see Figure 4).

Table 1 Parameters of the lower group coal containing

collapse column model

Stratum Thickness (m)

V P (m/s)Density (g/cm 3)Mudstone 1983500 2.3Coal 122000 1.8Mudstone 2203500 2.3Coal 232000 1.8Limestone 3773500 2.3Collapse column

——

1800

1.6

The model parameters are listed Table 1. The forward modeling is calculated using the finite different method (Wang, et al., 2004). The computation mesh is 0.5 m × 0.5 m and the acquisition parameters are: the receiving array has a trace interval of 2 m with 101 total traces and the shot interval is 10 m with 21 total shots. The synthetic seismogram parameters are: sampling frequency is 0.2 ms, record length is 150 ms, and main wavelet frequency is 300 Hz.

Distance (m)

20

-20

-60

-140

-180

)

m (h t p e D Fig. 4 Model of lower group coal containing a collapse

column.

(a) 30 ms (b) 34 ms (c) 41 ms

(d) 46 ms (e) 50 ms (f) 59 ms

Fig. 5 Snapshots of forward modeling wave ? eld of the lower group coal containing the collapse column.

Distance (m)

0100

200050100150200

D e p t h (m )Distance (m)

100

200Distance (m)

0100

200

In Figure 4 Model depth and length are both 200 m. The mine laneway is at a depth of 0 m and the collapse column is an irregular column with a small top and large base. The column has a maximum diameter of 4 m and a height of 45 m. The distance between column top and mine laneway is 85 m. The angle of top column wall varies from 60° to 70° from top to bottom and the base has a maximum angle of 90°. The P-wave velocity of the filled column is 1800 m/s.

Distance (m)

100

200

050100150200

D e p t h (m )

Distance (m)

100

200

Distance (m)

100

200

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Characteristics of the scattered waves

The snapshots of the shot point at 100 m are illustrated in Figure 5. The incident seismic wave encounters the small column top and generates a scattered wave which has weak back scattered energy in Figure 5a. In Figure 5b, the seismic wave propagates to coal seam 1 and reflection occurs. The breaking point of coal seam 1 has an obvious scattered wave which interferes with the column wall scattered wave. In Figure 5c a reflected wave is generated by coal seam 2 and the two coal layers strong scattered waves mutually interfere. In Figure 5d, the incident wave propagates from the top to the base of the column and scattered waves from multiple points mutually interfere. The strong scattered waves and the multiple scattered waves from the column result in a complicated wavefield. In Figure 5e, the reflected wave from coal seam 2 propagates to coal seam 1 and is reflected down again as an interlayer multiple. In Figure 5f, the scattered waves from the top, base, and walls of the collapse column interfere with the scattered waves reflected from the coal seams, forming several groups of strong scattered energy propagating upward.

Characteristics of scattered wave in synthetic shot records The shot gathers at positions of 60 m, 100 m, and 140 m are shown in Figure 6 and the following conclusions can be made: (1) The collapse column cannot form obvious interface reflection waves and the energy mainly behaves as scattered waves. (2) There is no scattered wave blind area in the shot gathers and the scattered energy concentrates in the direction of reflection rays. (3) Scattered waves from each point mutually interfere. (4) The scattered energy is much weaker than that of interface reflection waves. (5) The spatial position of the scattered point is always on the vertex of scattered wave’s time-distance curve, which does not change with the roll-along of the shot point. (6) The scattered energy from the base of the collapse column is stronger than that of any other point. There are two main reasons: the first is that the wavelength is near the diameter of the collapse column and the second is the incident angle is small at the base of the collapse column. (7) The wave field is very complex due to the mutual interference of the multiple scattered waves from the collapse column.

Fig. 6 Synthetic shot records of the lower group coal seam containing the collapse column.

Characteristics of scattered waves in CSP and CMP gathers

We gain CSP gathers by the previously mentioned CSP gather extraction method from synthetic single shot records with the following parameters: maximum equivalent offset is 100 m, and the equivalent offset step is 2 m (same as the trace interval). The three CSP gathers at the positions of 60 m, 100 m, and 140 m are shown in Figure 7a and the corresponding CMP gathers are shown in Figure 7b. Comparing the CSP and CMP gathers, we see: (1) The fold is different. Generally, the fold of each CMP is determined by geometry. The CSP fold is related to the two extraction parameters, maximum equivalent offset and equivalent offset step, and it will be higher if the equivalent offset step is smaller or maximum equivalent offset is larger. However, not every trace can contribute to the stack when we select too large a maximum equivalent offset and have more traces in the CSP gathers. The number of traces contributing to the stack is called the effective fold in this paper. Actually, the maximum equivalent offset should be determined comprehensively by both recording time length and offset. The three CSP gathers at 60 m, 100 m, and 140 m all have 101 traces and the effective fold is 81, 101, and 81, respectively, determined by the maximum equivalent offset, offset step, and CSP location together

50100

49

99

48

98

Chan

4080

120

T i m e (m s )

Shot 6161141141101101Scattered wave from collapse column Internal multiple from coal 1and 2Internal multiple from collapse column

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Fig. 7 (a) CSP gathers and (b) CMP gathers from the collapse column model.

Effects analysis of scattered and reflection imaging

Using the imaging method, 51 CSP gathers are extracted and the parameters chosen are: extraction interval is 4 m, maximum equivalent offset is 100 m,

and equivalent offset step is 2 m. We calculated the Kirchhoff integral along the scattering hyperbolas for each CSP gather and the EOM section is shown in Figure 8a with CSP interval equal to 4 m. The interference stack

10302050

40Chan

4080120T i m e (m s )

206040100

80Chan

40

80

120

T i m e (m s )

(a) EOM section (b) Interference stack migration

as shown in figure7a. In contrast to the CSP gathers at same locations, CMP gather fold is only 13, 21, and 13. (2) In CSP gathers, the time-distance curves of scattered waves are hyperbolic and reflected waves are consistent with the reflection interfaces. In CMP gathers, time-distance curves of reflected and scattered waves are all hyperbolic. (3) Spatial position information is consistent with the model and the vertex of the scattered wave

hyperbola is the real position of the scattered point. CMP gathers scattered waves are submerged in the reflected waves. (4) CSP gathers actually are zero-offset sections and target morphology can be directly observed. (5) Reflected waves are formed by interference enhancement of multiple scatter points, the energy is strong, and the discontinuity point of reflection event is the position of the coal breaking point.

61

61

101

101

141

141

CSP

4080

120

Scattered wave Retlection wave

T i m e (m s )

Effective fold: 81

Effective fold: 101

Effective fold: 81

CMP

4080

120

T i m e (m s )

61

61101101101141141141

Scattered wave Retlection wave

Fold: 13Fold: 21

Fold: 13

101(a)

(b)

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section is shown in Figure 8b with a CSP interval of 2 m, and the migration after stack section based on CMP gathers is shown in Figure 8c with a CDP interval of 1 m. Contrasting the three methods results, we can draw some conclusions: (1) The best imaging result is shown in Figure 8b. In the figure, we see that the collapse column scattered wave migration is accurate and its external morphology is clear, especially for the base of the column, its lateral scale equates with the seismic wave length, and the angle is quite small. (2) There are almost no diffractions in Figure 8a but we didn’t make full use of the weak scattered wave information. We only see the column’s vague morphology. The CSP extraction interval is equivalent with the maximum diameter of column, i.e., 4 m, so lateral resolution is low. We can decrease the extraction interval to improve the lateral resolution depending on computer memory and computation speed. (3) Seismic data corresponding to the top of the column is quite complex and it is too difficult to obtain accurate velocity data so the stack migration is not ideal and the column morphology is not clear while scattering wave imaging is less dependent in velocity. Scattered imaging shows better results with the same velocity analysis (as shown in Figures 8a and 8b).

Summary of the numerical simulation

(1) Scattered wave intensity is related to not only the shape of scattered body, impedance difference, and incident angle but also the seismic wave length and scale of the scattering body. The intensity of the scattered wave is strongest when seismic wave length equates with the scale of the scattering body.

(2) Stacking velocity has no certain geological implication for scattered imaging processing, which is only an imaging parameter. Traditional velocity analysis

can not determine the real velocity of the scattering body, so scattered energy cannot be wholly converged by post-stack Kirchhoff migration.

(3) We make use of more traces and an enlarged offset range when extracting CSP gathers. So we increase fold and improve the signal to noise ratio. It provides correct imaging of complex structure, steep angle interfaces, and heterogeneous geologic bodies.

Detection simulation ahead of laneway

Model parameters and observation method

The diffraction stack migration method widely applies in seismic laneway prediction (Zhang, et al, 2007) although some problems also exist. This method is based on ray theory without considering the seismic wave’s dynamic characteristics. The imaging result has strong diffractions which affect interpretation accuracy. We build the observation method the same as the Tunnel Seismic Prediction (TSP) technique and also use the EOM method based on the wave equation to improve the imaging result.

Based on the special mine exploration conditions and the detection goal, the laneway advanced prediction model is shown in Figure 9. Forward modeling is calculated using the finite different method (Wang, et al., 2004). The computation mesh is 0.5 m × 0.5 m.

50100200

150CMP

4080

120

T i m e (m s )

(c) CMP post-stack Kirchhoff migration

Fig. 8 Time sections of the collapse column model

migration imaging.

Distance (m)

2040

6080100120140160180200

200-20-40-60-80-100-120-140-160-180-200

D e p t h (m )

100m

50m

60m

①60shot

receiver

o ②

③④

Fig. 9 Roadway advanced detection model.

Model length is 200 m and total depth of model is 220 m. The mine laneway is at depth of 0 m. Shot points and geophones are on the laneway ? oor. The acquisition parameters includes: trace interval is 2 m, total traces 30, total one shot, and full receiver array receiving,with offset 22 m. Shot abscissais is 0 m and the receiver array extends from 22 m to 80 m.

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Table 2 Parameters of the laneway advanced prediction model

https://www.360docs.net/doc/c49269394.html, V P (m/s)Density(g/cm 3)

Other ①Coal roadway 3400.0013Depth 3m ②Coal seam 2000 1.8Thickness 5 m ③Fault fracture zone 25002Influencing width 2 m

④Surrounding rock 3500 2.3——⑤

Karst cave

1500

1

Scale 5 m × 5 m

Synthetic single shot record

51530

25Chan

4080120T i m e (m s )

51530

25Chan

40

80

120

T i m e (m s )

The synthetic single shot record is shown in Figure

10. Figure 10a is the original synthetic seismic record and Figure 10b is the record after preprocessing, such as F-K filter and interference wave mute. The direct wave, roadway head reflection, and the multi-reflection wave between the fault plane and coal seam are suppressed. The P- wave velocity and density of surrounding rock are higher than that of karst, so the scattered waves, generated from the top and bottom of karst, are different in phase. Otherwise, the travel time of the scattered waves from different point are also different, so the scattered waves from the top and bottom of karst are easily indentified, shown by and in figure 10a.

Effects analysis between EOM and diffraction stack migration

We apply our method to extract CSP gathers from (a) Original synthetic record (b) Record after preprocessing

Fig. 10 Synthetic single shot record of the roadway advanced prediction model.

(① Directive wave, ② Re? ection wave from laneway heading, ③ Scattered wave from ? oor of the karst, ④ Scattered wave from bottom of the

karst, ⑤ Re? ection wave of fault fracture zone, ⑥ Interference of multi-re? ection wave between fault plane and coal seam)

the record in Figure 10b. The parameters chosen are CSP point interval 4 m, maximum equivalent offset 150 m, and equivalent offset step 2 m (generally using the trace interval). Then the extracted CSP gathers are used to image by the EOM method and then Figure 11a is obtained after time-depth conversion. The diffraction stack migration result is shown in Figure 11b. Some conclusions follow from the two figures: (1) the two methods have satisfactory results. The karst cave position and fault fracture zone are consistent with the model. (2) The scattered imaging technique’s resolution is almost equivalent to the diffraction stack, although the scattered imaging advantages are not realized because of the TSP observation restrictions. Actually, the diffraction stack migration has a limited anti-interference ability. Therefore we can combine the two techniques to improve the interpretation accuracy.

The synthetic seismogram parameters are: sampling frequency is 0.2 ms, record length is 150 ms, the

wavelet main frequency is 300 Hz, consistent with real data.

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50

100150

200

0-40-80-120-160-200

D e p t h (m )

Distance (m)0.80.60.40.20-0.2-0.4-0.6-0.8

050

100150

200

0-40-80-120-160-200

D e p t h (m )

Distance (m)

0.80.60.4

0.20-0.2-0.4-0.6-0.8

(a) Depth section from EOM migration (b) Depth section from diffraction stack migration

Fig.11 Migration depth sections of the roadway advanced prediction model.

Conclusions

(1) Compared with reflected wave imaging, the

scattered imaging method is more applicable for mine prospecting, especially with the conditions that geological bodies have complex structure or that reflection information is quite weak and has low SNR. This method has high fold, accurate migration and can effectively improve imaging quality.

(2) We also applied scattered imaging to mine laneway advanced prediction and the combination with the diffraction stack method can improve interpretation precision.

(3) The key step of scattered imaging is the extraction of CSP gathers, which involves parameters, such as maximum equivalent offset, equivalent offset step, and the velocity model. It is very necessary to generalize the principles for determining these extraction parameters. (4) The scattered imaging technique in deep mines is still undeveloped and is an important subject for future study. The main tasks are: determining the scattered wave field characteristics over the entire mine region, designing geometry and field construction, improved scattered imaging processing techniques, and recognition and interpretation techniques for scattered waves based on forward modeling and inversion.

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Yin, J. J., 2005, A study on seismic scattered wave characteristics by numerical simulating: PhD Thesis, China University of Geosciences, Beijing.

Zhang, L. Y. and Liu, Y., 2006, Analysis and application of pseudo-offset method in the converted-wave prestack time migration: Applied Geophysics, 3(1), 18 – 26. Zhang, L. Y. and Liu, Y., 2008, Anisotropic converted wave amplitude-preserving prestack time migration by the pseudo-offset method: Applied Geophysics, 5(3), 204 – 211.Zhang, P. S., Liu, S. D. and Wu, J. S., 2007, Study on detecting simulation ahead of tunnel and laneway and its migration techniques: Chinese Journal of Rock Mechanics and Engineering, 26(1), 2847 – 2851. Zhang, T. X., Tao, G., Li, J. J., Wang, B., and Wang, H., 2009, Application of the equivalent offset migration method in acoustic log reflection imaging: Applied Geophysics, 6(4), 303 – 310.

Zhu, G. W., Di, B. Y., Ma, W. B., Wu, C. X., and Ding, X., 2008, Geological conditions and other geophysical survey technologies of coal mining face in deep mine: Coal Engineering (in Chinese), 55(3), 66 – 68.

Hu Ming-Shun received a B.E. (2008) in Image

Engineering from China

University of Mining And

Technology. Currently he is

studying for his PhD at China

University of Mining And

Technology of Geophysics.

His interests are mine seismic

exploration research and

application.

282

韩立国1,牛建军2,张晓培2,王德利1,杜立志2,Applied Geophysics, 7(3), P.265 - 271.

(1.吉林大学 地球探测科学与技术学院,长春,130026;2.吉林大学建设工程学院,长春,130026)

摘要:本文提出了一种基于Kirchhoff积分偏移和逆时偏移的联合速度分析及成像方法,采用剩余曲率分析及层剥离策略进行偏移速度建模。本文方法改善了Kirchhoff积分偏移在复杂构造时计算精度不高和逆时偏移计算效率慢的缺点,兼有计算效率高、成像精度高的优点,并将其应用在反射波法隧道超前预报中。通过模型试算,发现隧道中使用逆时偏移的成像结果在多方面优于Kirchhoff积分偏移的成像结果;通过对实测数据的处理,验证本方法计算效率较高,建立的速度模型合理,成像剖面清晰,结合地质调绘资料可对隧道开挖前方地质构造做出较准确预报。

关键字:隧道预报,偏移速度分析,Kirchhoff积分偏移,逆时偏移,速度建模

深部矿井地震散射波成像数值模拟//Numerical simulation of scattered imaging in deep mines,胡明顺1,2 潘冬明1,2,李娟娟1,3,Applied Geophysics, 7(3), P.272 - 282.

(1、 中国矿业大学 资源与地球科学学院 江苏 徐州 221116;2、中国矿业大学 深部岩土力学与地下工程国家重点实验室 江苏 徐州 221116;3、中国矿业大学 煤层气资源与成藏过程教育部重点实验室 江苏 徐州 221116)

摘要:常规地震勘探大多基于反射波理论,对尺度小、倾角陡、构造复杂的灾害性地质体,很难得到精确的成像结果。本文建立2类典型矿井地质模型,采用有限差分正演模拟算法,研究了矿井地震散射波的特征,将等效偏移距偏移(EOM)和基于等效偏移距干涉叠加偏移的散射成像方法用于矿井地震勘探中,重点分析了散射波成像相比常规反射波地震成像的技术优势。研究表明:1)散射成像方法能够提高覆盖次数,充分利用有效的弱散射信号,对不均匀复杂地质体的散射波的成像效果明显优于反射波叠后偏移;2)对于巷道超前探测,它弥补了基于射线理论的叠加偏移的不足,为提高矿井地震勘探分辨率提供了有效的成像方法。

关键词:矿井,地震勘探,散射波,地震成像,数值模拟

一种评价致密砂岩储层孔隙结构的新方法及其应用//A Novel model to assess the pore-structure of tight sands and its application,李潮流,周灿灿, 李霞, 胡法龙, 张莉, 王伟俊,Applied Geophysics, 7(3), P.283 - 291.

(中国石油勘探开发研究院, 中国北京,100083)

摘要:致密砂岩储层的孔隙结构对其渗透性和电性影响显著,是此类复杂储层岩石物理研究的关键。针对仅从连通喉道半径评价渗透率的多解性以及储层孔隙结构与电性关系研究欠缺等不足,综合影响物性的主要因素,提出了一种同时考虑孔隙度、最大连通喉道半径及分选性三种因素的新型孔隙结构参数δ的计算公式。利用岩心及实测数据对比分析表明,δ值能够较连通喉道半径等传统方法更精确地刻画致密砂岩储层渗透性,同时它与储层电性具有密切关系,可用于估算地层因素F和胶结指数m。据此提出将孔隙结构对电阻率的影响进行归一化校正以及基于核磁共振测井预测储层完全含水电阻率R0的评价方法,从而突出储层流体性质变化引起的电性变化,并提供了一种新的致密砂岩储层流体识别思路,研究结果得到了实验资料和实际测井试油资料的验证。

关键词:低孔低渗 致密砂岩,孔隙结构,核磁共振,岩石物理

294

地震波运动学理论

第二章地震波运动学理论 一、名词解释 1. 地震波运动学:研究在地震波传播过程中的地震波波前的空间位置与其传播时间的关系,即研究波的传播规律,以及这种时空关系与地下地质构造的关系。 2. 地震波动力学:研究地震波在传播过程中波形、振幅、频率、相位等特征的及其变化规律,以及这些变化规律与地下的地层结构,岩石性质及流体性质之间存在的联系。 3. 地震波:是一种在岩层中传播的,频率较低(与天然地震的频率相近)的波,弹性波在 岩层中传播的一种通俗说法。地震波由一个震源激发。 4. 地震子波:爆炸产生的是一个延续时间很短的尖脉冲,这一尖脉冲造成破坏圈、塑性带,最后使离震源较远的介质产生弹性形变,形成地震波,地震波向外传播一定距离后,波形逐渐稳定,成为一个具有2-3个相位(极值)、延续时间60-100毫秒的地震波,称为地震子波。地震子波看作组成一道地震记录的基本元素。 5.波前:振动刚开始与静止时的分界面,即刚要开始振动的那一时刻。 6.射线:是用来描述波的传播路线的一种表示。在一定条件下,认为波及其能量是沿着一条“路径”从波源传到所观测的一点P。这是一条假想的路径,也叫波线。射线总是与波阵面垂直,波动经过每一点都可以设想有这么一条波线。 7. 振动图和波剖面:某点振动随时间的变化的曲线称为振动曲线,也称振动图。地震勘探中,沿测线画出的波形曲线,也称波剖面。 8. 折射波:当入射波大于临界角时,出现滑行波和全反射。在分界面上的滑行波有另一种特性,即会影响第一界面,并激发新的波。在地震勘探中,由滑行波引起的波叫折射波,也叫做首波。入射波以临界角或大于临界角入射高速介质所产生的波 9.滑行波:由透射定律可知,如果V2>V1 ,即sinθ2 > sinθ1 ,θ2 > θ1。当θ1还没到90o时,θ2 到达90o,此时透射波在第二种介质中沿界面滑行,产生的波为滑行波。 10.同相轴和等相位面:同向轴是一组地震道上整齐排列的相位,表示一个新的地震波的到达,由地震记录上系统的相位或振幅变化表示。 11.地震视速度:当波的传播方向与观测方向不一致(夹角θ)时,观测到的速度并不是波前的真速度V,而是视速度Va。即波沿测线方向传播速度。 12 波阻抗:指的是介质(地层)的密度和波的速度的乘积(Zi=ρiVi,i为地层),在声学中称为声阻抗,在地震学中称波阻抗。波的反射和透射与分界面两边介质的波阻抗有关。只有在Z1≠Z2的条件下,地震波才会发生反射,差别越大,反射也越强。 13.纵波:质点振动方向与波的传播方向一致,传播速度最快。又称压缩波、膨胀波、纵波或P-波。 14.横波:质点振动方向与波的传播方向垂直,速度比纵波慢,也称剪切波、旋转波、横波或S-波,速度小于纵波约0.7倍。横波分为SV和SH波两种形式。 15.体波:波在无穷大均匀介质(固体)中传播时有两种类型的波(纵波和横波),它们在介质的整个立体空间中传播,合称体波。 16共炮点反射道集:在同一炮点激发,不同接收点上接收的反射波记录,称为共炮点道集。在野外的数据采集原始记录中,常以这种记录形式。可分单边放炮和中间放炮。 17.面波:波在自由表面或岩体分界面上传播的一种类型的波。 18.纵测线和非纵测线:激发点与接收点在同一条直线上,这样的测线称为纵测线。用纵测线进行观测得到的时距曲线称为纵时距曲线。激发点不在测线上,用非纵测线进行观测得到的时距曲线称为非纵时距曲线。

多波多分量地震波场数值模拟及分析

第46卷第5期2007年9月 石油物探 GEOPHYSICALPROSPECTINGFORPETRoI。EUM V01.46,No.5 Sep.,2007 文章编号:1000—1441(2007)05—0451—06 多波多分量地震波场数值模拟及分析 刘军迎,雍学善,高建虎,杨午阳 (中国石油天然气股份有限公司勘探开发研究院西北分院,甘肃兰州730020) 摘要:以多波多分量地表资料处理和解释为目的,利用波动方程数值模拟方法对多波多分量地震波场进行了分析和研究。通过单界面和双界面模型正演,对反射纵波(PP波)和转换横波(P-SV波)的识别及波场响应特征进行了研究:①P-SV波速度低,频率低,能量随偏移距的增加而增加,零偏移距处能量为零;②界面反射系数为正时P-SV波与PP波极性相反,界面反射系数为负时P-SV波与PP波极性一致;③Z分量和X分量地震记录都是PP波与P-SV波的混合信息;④X分量的PP波和P.SV波都是由两个极性相反的分支组成的。通过多界面模型正演,分析了转换波勘探的多解性,即地质上的同一个岩性界面有可能对应地震剖面上的两个甚至更多的同相轴。通过理论、模型和实际资料分析,探讨了多波多分量勘探中水平分量旋转处理存在的问题,即通过水平分量旋转处理获得的三分量记录仍然包含了全波场信息,指出通过极化分析,进行三分量同时旋转,可以实现纵波波场和横波波场的完全分离。最后讨论了PP波和P-SV波的分辨率,认为P-SV波的纵、横向分辨率均低于PP波。 关键词:多波多分量;波场特征;水平分量旋转;三分量旋转;波场分离;分辨率 中图分类号:P631.4文献标识码:A 数值模拟技术已广泛应用于油气勘探的各个阶段,如模型正演AVO研究[1],叠前深度偏移的初始速度模型建立[2],等等。数值模拟方法主要有两大类,即波动方程法和几何射线法[3]。几何射线法以研究波的运动学特征为主,适合地质构造的模拟与研究,但该方法缺乏对波的动力学特征的表征能力,不适合多波多分量地震波场的表征、刻画和研究;波动方程法具有同时表征波场的运动学特征和动力学特征的能力,是地震波(包括P波、PS波等)的传播机理、波场响应特征研究和分析的有力工具。 有人利用Aid近似公式进行多波多分量记录合成,研究弹性参数的反演问题[4],但因为基于褶积模型,不算真正意义上的模型正演。我们利用全波场波动方程数值模拟技术分析了多波多分量地震波场的传播特征和地层响应特征;对目前的水平分量旋转处理技术进行了讨论,指出其存在的不足,给出了应对策略,同时还对转换横波的地震分辨率进行了分析,为多波多分量资料处理和解释提供了参考依据。 1PP波、P-SV波的识别和波场特征研究 研究中遵循的指导思想是“由简单到复杂”:由单界面模型到多界面模型,由声波方程到弹性波方程,由单分量(Z分量)波场到多分量(Z分量、X分量)波场。 1.1PP波、P-SV波的识别 图1是设计的单界面模型,地层1的纵波速度为3000.00m/s,横波速度为1730.00m/s,密度为2.20g/C1.n3;地层2的纵波速度为4724.49m/s,横波速度为2737.45m/s,密度为2.57g/crn3。图2是弹性波动方程法模拟的单炮记录和波场快照,可以看出,转换横波(P_SV波)的同相轴位于反射纵波(PP波)同相轴的下方,曲率较大。这说明P_SV波传播速度较小,在同一反射层、同一反射/转换点的情况下,旅行时较大。由公式 vf,s一2vpvs/(Vp—l—vs) 及 to==2h/v 也可以得出这样的结论,并且P-SV波和PP波的速度差异越大,二者分得越开,在单炮记录或地震剖面上就越容易识别。 图1单界面模型 收稿日期i2006—12—04;改回日期:2007—03—01。 作者简介:刘军迎(1966一),男,高级工程师,现从事多波多分量地 震波场数值模拟和资料解释等研究工作。 万方数据

地震波层析成像反演方法及其研究综述

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midas数值模拟软件应用

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图2.2.2(b)4-4剖面Z方向应力变化色谱图 3三维模型 三维模型共有24692个节点,29736个单元(如图3)。破坏判据采用莫尔-库仑准则。模型参数取表1。沿走向开挖10步,前3步20m,中间4步10m,后3步20m,共开挖160m。 图3 4-4剖面三维数值模型 3.1第一步开挖 3.1.1位移云图

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目录 1 选题依据 (2) 1.1 选题意义 (2) 1.2 国内外研究现状分析 (3) 2 论文研究方案 (4) 2.1 研究目标 (4) 2.2 研究内容与方法 (5) 2.3 技术路线 (5) 2.4 关键技术与难点 (6) 3 预期目标与研究成果 (6) 4 工作计划 (7) 5 参考文献 (7)

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