CN102455439A - Diffracted wave field separation method based on Kirchhoff integral method - Google Patents

Abstract

The invention provides a diffracted wave field separation method based on a Kirchhoff integral method. In seismic exploration, subsurface information can be inferred through responses of seismic waves to subsurface media; when a subsurface medium catastrophe happens, diffracted waves usually are response to the subsurface medium catastrophe. Main oil gas storage spaces in carbonate rock regions (such as Tarim and Sichuan) are secondary corroded holes and cracks, the sizes of the holes and the cracks are smaller than the wavelength of the seismic waves; the seismic response of the holes and the cracks is mainly diffraction, therefore the research on the diffracted waves has significant theoretical and practical meanings. However, in common deviation, the diffracted waves are converged to be one point on a profile and are submerged in a plurality of events and cannot be recognized. In a common reflection point (CRP) trace gather, since diffraction points and reflection points are the flattening of the events, the diffraction points cannot be recognized in the trace gather. Therefore, the invention provides a method for outputting an inclined angle trace gather through Kirchhoff deviation and hole diffracted waves and interface reflection waves can be rapidly and efficiently separated through obvious difference between the reflection waves and the diffracted waves in the inclined angle trace gather.

Description

Diffracted wave field separation method based on the kirchhoff integral method

Technical field

The present invention relates to the exploration of oil and gas field technical field, belong to seismic signal and analyze category, a kind of specifically seam hole imaging technique based on the kirchhoff integral method.

Background technology

For complex dielectrics; Like the Tarim Basin; Oil gas preserves in ancient Cambrian system and ORDOVICIAN CARBONATE stratum; The buried depth on these stratum below 5000m, primary pore is compacted already, filling totally, reservoir space of today is the secondary pores that leans on effect such as corrosion, fracture to form the day after tomorrow.The distribution of these holes does not receive the control of sedimentary facies belt, and the scale that distributes and inhomogeneous.Therefore, wanting to seek these hole seam type reservoirs can only be through the means of earthquake.

The size of corrosion hole often wants much little than the wavelength of seismic event, can think the catastrophe point of lithology.Diffraction will take place in seismic event on the catastrophe point of lithology, as long as detect these diffracted waves, through the seismic migration technology, diffracted wave is restrained, and just can confirm the position of corrosion hole.Yet the fact is so not simple, and on the section after the skew, diffracted wave is often converged a point, thereby is submerged between numerous reflection line-ups, is difficult for differentiating.In the CRP gather after common migration before stack (CRP), diffraction point and reflection spot show as evening up of lineups again equally, therefore, can not distinguish reflection wave and diffracted wave through the CRP gather (CRP) of migration before stack.

At present also be in the starting stage in the research aspect the diffracted wave field separation both at home and abroad, also do not have the Study on forming achievement.On-the-spot in exploration, diffracted wave is still the difficult problem of processing.Under many circumstances, owing to there is not effective separation means, can only diffracted wave be suppressed as a kind of interference.But so, underground medium sudden change information has just been lost, and resolution of seismic prospecting also descends thereupon.Therefore, petroleum prospecting industry is especially faced and is pressed for a kind of effective diffracted wave field separation method when having the complicated reservoirs of corrosion hole.

Summary of the invention

The invention is intended to provide a kind of through the high s/n ratio seismic data; Through kirchhoff skew output inclination angle Dao Ji; Obtain the independent imaging results of diffracted wave according to the obvious difference of concentrating diffracted wave and reflection wave in the road, inclination angle; Thereby the geology catastrophe point to underground is carried out meticulous imaging, so that better recognition carbonate grotto seam reservoir.

The technical scheme that the interval velocity field realization above-mentioned purpose that high s/n ratio seismic data that this patent use was handled and high precision velocity analysis obtain is taked is following:

Step 1: use the interval velocity model of input to carry out ray tracing, obtain the cautious whilst on tour tabulation of each big gun of ground.The rapid finite difference ray casting that ray tracing can select Vidale (1988) to propose.

Step 2: kirchhoff method output inclination angle Dao Ji:

At first, read in the input geological data one.And read in the right whilst on tour tabulation of this together corresponding big gun inspection that step 1 obtains respectively;

Secondly, calculate underground each point place's incident ray and reflected ray angle through following formula with vertical direction:

$\tan {\mathrm{\α}}_s=\frac{{\∂\mathrm{\τ}}_s/\∂x}{\∂{\mathrm{\τ}}_s/\∂z}$

$\tan {\mathrm{\α}}_r=\frac{{\∂\mathrm{\τ}}_r/\∂x}{\∂{\mathrm{\τ}}_r/\∂z}$

In the formula: τ _sBe shot point whilst on tour, τ _rBe geophone station whilst on tour, α _sFor the angle r of incident ray and vertical direction is the angle of reflected ray and vertical direction, (x z) is volume coordinate.

According to geometric relationship, can obtain inclination angle theta, reflection angle

With α _s, α _rBetween relation

$\mathrm{\θ}=\frac{{\mathrm{\α}}_s+{\mathrm{\α}}_r}{2}$

Can know through ray tracing by above analysis, can set up the relation of shot point coordinate and calculation level coordinate and inclination angle theta and geophone station coordinate r

s＝s(x，z，r，θ)

And then the kirchhoff offset equation can be write as

$R(x,z,\mathrm{\θ})=\underset{\mathrm{\Γ}}{\∫}u(s(x,z,r,\mathrm{\θ}),r,{\mathrm{\τ}}_s+{\mathrm{\τ}}_r)\mathrm{dr}$

So just realized kirchhoff skew output inclination angle Dao Ji.

Step 3: the road, inclination angle in that step 2 obtains is concentrated, and reflection wave shows as the curve of a upward opening, and the diffracted wave of observation shows as a horizontal linear directly over diffraction point.Therefore, can both be separated through the method for medium filtering.Can carrying out of medium filtering according to following operation:

At first, read in an inclination angle Dao Ji.

Secondly, constitute a sequence, this sequence is pressed (from big to small) ordering from small to large for the amplitude of getting its adjacent several roads same depth point by way of each depth point in each road of concentrating.

At last, get of the filtering output of the intermediate value of above-mentioned sequence as this this depth point, road.

Step 4: road, the inclination angle collection stack of the filtering output that step 3 is obtained just can generate the independent imaging section of diffracted wave.

Above embodiment only is used to explain the present invention, but not is used to limit the present invention.

Description of drawings

Horizontal reflection INTERFACE MODEL of Fig. 1 (a);

Fig. 1 (b) is the inclination angle Dao Ji at Fig. 1 (a) horizontal reflection interface of observation at the x=0 place;

Inclination angle of Fig. 1 (c) is 25 ° a tiltedinterface model;

Fig. 1 (d) is the inclination angle Dao Ji of Fig. 1 (c) tiltedinterface of observation at the x=0 place.

The single diffraction point model of Fig. 2 (a);

Fig. 2 (b) is the inclination angle Dao Ji of Fig. 2 (a) institute representation model when observing at the x=0 place;

Fig. 2 (c) is the inclination angle Dao Ji of Fig. 2 (a) institute representation model when observing at the x=100m place;

Fig. 2 (d) is the inclination angle Dao Ji of Fig. 2 (a) institute representation model when observing at the x=-100m place;

Each parameter synoptic diagram of Fig. 3 ray tracing system.

Fig. 4 multilayered medium diffraction model.5 diffraction points are wherein arranged, lay respectively at x=2000m and x=2200m place.

Near in Fig. 5 model shown in Figure 4 the diffraction point several inclination angle Dao Ji.The road collection of black line mark is the x=2000m place.

Fig. 6 (a) is the inclination angle Dao Ji of black line mark among Fig. 5;

Fig. 6 (b) is the diffracted wave after road, inclination angle collection separates among Fig. 6 (a);

Fig. 6 (c) is the reflection wave after road, inclination angle collection separates among Fig. 6 (a).

Skew stacked section before Fig. 7 (a) separates model diffraction shown in Figure 4;

Skew stacked section after Fig. 7 (b) separates model diffraction shown in Figure 4.

Embodiment

Through a numerical model working of an invention process is described:

At first set up a multilayered medium rate pattern (as shown in Figure 4).5 diffraction points are wherein arranged, lay respectively at x=2000m and x=2200m place.There are two diffraction points at the x=2000m place, and the degree of depth is respectively 3000m and 4400m; There are three diffraction points at the x=2200m place, and the degree of depth is respectively 3000m, 4400m and 4800m.

Adopt Kirchhoff just to drill to model, adopt split shooting, 300 roads receive, and totally 300 big guns cover for 150 times, 2 milliseconds of samplings, and record length is 4 seconds.

Generate several inclination angle Dao Ji (as shown in Figure 5) through the said method of step 2 then.Concentrating reflecting interface in the road, inclination angle is the curve that is bent upwards, the corresponding inclination angle and the degree of depth of its extreme point indication.Diffraction point is concentrated in the road shown in the black line (x=2000m) and is well evened up, and concentrates on monotonous curve in other roads.

Separate diffracted wave and reflection wave road collection (as shown in Figure 6) afterwards through step 3 again.

Stacked section before and after at last diffracted wave field being separated compares (as shown in Figure 7).Can find out that on the stacked section (Fig. 7 (a)) before diffracted wave separates, the reflection of bed interface is very strong, has covered in the reflection of hole fully; Can't see the reflective information of bed interface on the stacked section of diffracted wave after separating (Fig. 7 (b)), the just reflective information (oval point among the figure) of hole that stays.

List of references

Vidale，J.E.，1988，Finite-difference?traveltime?calculation：Bull.，Seis.Sot.Am.，78，2062-2076.

Vidale，J.E.，1990，3-D?finite-difference?traveltime?calculation：Geophysics，55，523-528.

Claims (2)

1. Diffracted wave field separation method based on the kirchhoff integral method

   1. the invention is intended to provide a kind of through the high s/n ratio seismic data; Through kirchhoff skew output inclination angle Dao Ji; Obtain the independent imaging results of diffracted wave according to the obvious difference of concentrating diffracted wave and reflection wave in the road, inclination angle; Thereby the geology catastrophe point to underground is carried out meticulous imaging, so that better recognition carbonate grotto seam reservoir.

   The technical scheme that the interval velocity field realization above-mentioned purpose that high s/n ratio seismic data that this patent use was handled and high precision velocity analysis obtain is taked is following:

   Step 1: use the formation velocity model of input to carry out ray tracing, obtain the cautious whilst on tour tabulation of each big gun of ground.The rapid finite difference ray casting that ray tracing can select Vadile (1988) to propose.

   Step 2: kirchhoff method output inclination angle Dao Ji.

   Step 3: the road, inclination angle in that step 2 obtains is concentrated, and reflection wave shows as the curve of a upward opening, and the diffracted wave of observation shows as a horizontal linear directly over diffraction point.Therefore, can both be separated through the method for medium filtering.

   Step 4: road, the inclination angle collection stack of the filtering output that step 3 is obtained just can generate the independent imaging section of diffracted wave.
2. 2. the diffracted wave field separation method based on the kirchhoff integral method according to claim 1 is characterized in that, the method for road, the output inclination angle collection in the described step 2 is:

   At first, read in the input geological data one.And read in the right whilst on tour tabulation of this together corresponding big gun inspection that step 1 obtains respectively;

   Secondly, calculate underground each point place's incident ray and reflected ray angle through following formula with vertical direction:

   $\tan {\mathrm{\α}}_s=\frac{{\∂\mathrm{\τ}}_s/\∂x}{\∂{\mathrm{\τ}}_s/\∂z}$

   $\tan {\mathrm{\α}}_r=\frac{{\∂\mathrm{\τ}}_r/\∂x}{\∂{\mathrm{\τ}}_r/\∂z}$

   In the formula: τ _sBe shot point whilst on tour, τ _rBe geophone station whilst on tour, α _sAngle for incident ray and vertical direction _rBe the angle of reflected ray and vertical direction, (x z) is volume coordinate.

   According to geometric relationship, can obtain inclination angle theta, reflection angle With α _s, α _rBetween relation

   $\mathrm{\θ}=\frac{{\mathrm{\α}}_s+{\mathrm{\α}}_r}{2}$

   

   Can know through ray tracing by above analysis, can set up the relation of shot point coordinate and calculation level coordinate and inclination angle theta and geophone station coordinate r

   s＝s(x，z，r，θ)

   And then the kirchhoff offset equation can be write as

   $R(x,z,\mathrm{\θ})=\underset{\mathrm{\Γ}}{\∫}u(s(x,z,r,\mathrm{\θ}),r,{\mathrm{\τ}}_s+{\mathrm{\τ}}_r)\mathrm{dr}$

   So just realized Kirchhoff skew output inclination angle Dao Ji.

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