CN103576190B - A kind of method solving reverse-time migration waveform discontinuity - Google Patents

Abstract

The present invention is the method for the effective solution reverse-time migration waveform discontinuity that can improve oil reservoir fine description. Adopt interval velocity model in depth domain and just drilling big gun collection data, first choose focus wavelet, carry out single big gun wave equation in Depth Domain and just drill, store single big gun source Bo Chang of all moment; Then with single big gun seismologic record as initial boundary condition, just drilling along time axle counter movement wave equation from the maximum record moment and obtaining receiving ripple field, utilize the level and smooth image-forming condition that the present invention proposes, obtain waveform continuously after single big gun reverse-time migration imaging, all single big gun reverse-time migration imagings are carried out superposition and obtain reverse-time migration imaging. The present invention is in waveform continuity, along, in layer earthquake instantaneous frequency and phase place sky change stability, level and smooth image-forming condition is better than conventional image-forming condition.

Description

A kind of method solving reverse-time migration waveform discontinuity

Technical field

The present invention relates to exploration and reservoir geophysics technology, specifically a kind of method solving reverse-time migration waveform discontinuity.

Technical background

In exploration and reservoir geophysics, seismic migration imaging is a step of wherein most critical, and the quality of imaging directly has influence on follow-up earthquake and geologic interpretation, thus affects the identification of oil and gas reservoir. Seismic migration imaging can be divided into several big class: (1) offsets based on the Kirchhoff integration of ray theory; (2) based on F-K skew and the finite-difference migration of one way wave theory; (3) based on the reverse-time migration of round trip wave theory. (1) and (2) belong to conventional seismic migration, to complex geological structure such as horizontal speed acute variation, high steep dip angle etc., imaging capability is limited. And reverse-time migration is based on round trip wave theory, it can solve conventional seismic migration institute problems faced in theory, but also brings much new problem. Reverse-time migration comes imaging (Claerbout, 1971 based on the zero-lag cross-correlation of ripple field, source and reception ripple field; Biondi and Shan, 2002), it being different from conventional seismic migration, the waveform continuity of this kind of method can affect the fine degree of reservoir description, thus affects the accuracy of identification of oil and gas reservoir. How about solve when occurring that waveform is discontinuous, at present unmanned discussion in the world.

Waveform continuity (also claims slipperiness) and refers to whether waveform meets second derivative continuous. If meeting, represent that waveform is continuous print; If not meeting, represent that waveform is discontinuous. Reverse-time migration imaging mechanism is different from conventional seismic migration, its imaging waveform is discontinuous, it is the aggravation of waveform discontinuity with the increase of space mesh spacing, even if encryption space grid can not solve reverse-time migration waveform discontinuity problem to very little (1m*1m), this problem directly affects the effect of seismic prospecting.

Summary of the invention

The object of the invention is to provide a kind of method of effective solution reverse-time migration waveform discontinuity that can improve oil reservoir fine description.

The present invention is realized by following step:

1) acquiring seismic data, process obtains interval velocity model in depth domain and is just drilling big gun collection data;

2) utilize following formula to carry out single big gun wave equation in Depth Domain just to drill:

$\frac{1}{v^2}\frac{{\∂}^2{P}_s(X,t)}{\∂t^2}-{\mathrm{\ΔP}}_s(X,t)=\mathrm{\δ}(X-X_s)S\left(t\right),$

And store single big gun source Bo Chang in all moment;

Wherein: v is seismic wave speed, P_s(X, t) is single big gun source Bo Chang, �� is Laplace operator, �� (X-X_s) it is unit impulse function, S (t) is focus wavelet, and t is the time; X=(x, z) for ripple place is at two-dimensional space position coordinate, X_s=(x_s,z_s) it is two-dimensional space position, focus place coordinate, x and x_sIt is respectively ripple field and focus X-coordinate, z and z_sIt is respectively ripple field and focus ordinate zou;

3) with single big gun seismologic record as initial boundary condition, utilize following formula from the maximum record moment, just drill along time axle counter movement wave equation, obtain receiving ripple field:

$\frac{1}{v^2}\frac{{\∂}^2{P}_g(X,t)}{\∂t^2}-{\mathrm{\ΔP}}_g(X,t)=G(X_g,t);$

Wherein: P_g(X, t) is for receiving ripple field, G (X_g, t) it is single big gun seismologic record, X_g=(x_g,z_g) it is two-dimensional space position, wave-detector place coordinate, x_gFor wave-detector X-coordinate, z_gFor wave-detector ordinate zou;

4) when receiving ripple field backstepping, read mutually single big gun source Bo Chang in the same time, utilize following formula obtain waveform continuously after single big gun reverse-time migration imaging:

I_S(X)=S{ �� P_s(X,t)P_g(X, t) dt};

Wherein: S is for meeting second derivative continuous print smoothing operator;

Described smoothing operator adopts cubic spline function interpolation smoothing operator.

5) all single big gun reverse-time migration imagings are carried out superposition, obtain waveform continuously after superposition reverse-time migration imaging.

The present invention is in waveform continuity, along, in layer earthquake instantaneous frequency and phase place sky change stability, level and smooth image-forming condition is better than conventional image-forming condition.

Accompanying drawing explanation

Fig. 1 is theoretical model and single big gun seismologic record. A () is overthrust fault theoretical model; B () is a wherein big gun seismologic record.

Fig. 2 is the reverse-time migration imaging that obtains of different image-forming condition and waveform. (a) conventional image-forming condition; (b) level and smooth image-forming condition; C () is the partial enlargement of (a); D () is the partial enlargement of (b); E () is the waveform of scatter point P2 in (c); F () is the waveform of scatter point P2 in (d).

Fig. 3 is along layer L2 seismic attributes analysis. A () is along layer L2 layer flattened section (conventional image-forming condition); B () is along layer L2 layer flattened section (level and smooth image-forming condition); C () is along layer L2 instantaneous amplitude; D () is along layer L2 instantaneous frequency; E () is along layer L2 instantaneous phase; (on) conventional image-forming condition; (under) level and smooth image-forming condition; (f) instantaneous amplitude colour code; (g) instantaneous frequency colour code; (h) instantaneous phase colour code.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the present invention is described in detail.

The present invention is realized by following step:

1) acquiring seismic data, process obtains interval velocity model in depth domain (Fig. 1 (a), primarily of one group of uniclinal structure, an overthrust fault and three scatter points composition) and just drilling big gun collection data (Fig. 1 (b), for wherein a big gun seismologic record);

2) utilize following formula to carry out single big gun wave equation in Depth Domain just to drill:

$\frac{1}{v^2}\frac{{\∂}^2{P}_s(X,t)}{\∂t^2}-{\mathrm{\ΔP}}_s(X,t)=\mathrm{\δ}(X-X_s)S\left(t\right),$

And store single big gun source Bo Chang in all moment;

Wherein: v is seismic wave speed, P_s(X, t) is single big gun source Bo Chang, �� is Laplace operator, �� (X-X_s) it is unit impulse function, S (t) is focus wavelet, and t is the time; X=(x, z) for ripple place is at two-dimensional space position coordinate, X_s=(x_s,z_s) it is two-dimensional space position, focus place coordinate, x and x_sIt is respectively ripple field and focus X-coordinate, z and z_sIt is respectively ripple field and focus ordinate zou;

3) with single big gun seismologic record as initial boundary condition, utilize following formula from the maximum record moment, just drill along time axle counter movement wave equation, obtain receiving ripple field:

$\frac{1}{v^2}\frac{{\∂}^2{P}_g(X,t)}{\∂t^2}-{\mathrm{\ΔP}}_g(X,t)=G(X_g,t);$

Wherein: P_g(X, t) is for receiving ripple field, G (X_g, t) it is single big gun seismologic record, X_g=(x_g,z_g) it is two-dimensional space position, wave-detector place coordinate, x_gFor wave-detector X-coordinate, z_gFor wave-detector ordinate zou;

4) when receiving ripple field backstepping, read mutually single big gun source Bo Chang in the same time, utilize following formula obtain waveform continuously after single big gun reverse-time migration imaging:

I_S(X)=S{ �� P_s(X,t)P_g(X, t) dt};

Wherein: S meets second derivative continuous print smoothing operator to ensure the continuity of imaging waveform, described smoothing operator adopts cubic spline function interpolation smoothing operator;

5) all single big gun reverse-time migration imagings are carried out superposition, obtain waveform continuously after superposition reverse-time migration imaging.

Above step 2) to 5) can realize in a routine package, directly run and can obtain final result. From imaging waveform (Fig. 2 (e), (f)) it may be seen that the waveform that the level and smooth image-forming condition that the present invention proposes obtains is continuous print, and the waveform that conventional image-forming condition obtains is discontinuous. From becoming stability along layer L2 earthquake instantaneous frequency (Fig. 3 (a)), instantaneous phase (Fig. 3 (b)) along layer sky, the level and smooth image-forming condition that the present invention proposes is better than conventional image-forming condition.

In sum, in waveform continuity, becoming in stability along layer earthquake instantaneous frequency and phase place sky, the level and smooth image-forming condition that the present invention proposes is better than conventional image-forming condition.

Claims (2)

1. solving a method for reverse-time migration waveform discontinuity, feature is realized by following step:

1) acquiring seismic data, process obtains interval velocity model in depth domain and is just drilling big gun collection data;

2) utilize following formula to carry out single big gun wave equation in Depth Domain just to drill:

$\frac{1}{v^2}\frac{{\∂}^2{P}_s(X,t)}{\∂t^2}-\mathrm{\Δ}{P}_s(X,t)=\mathrm{\δ}(X-X_s)S\left(t\right),$

And store single big gun source Bo Chang in all moment;

Wherein: v is seismic wave speed, P_s(X, t) is single big gun source Bo Chang, �� is Laplace operator, �� (X-X_s) it is unit impulse function, S (t) is focus wavelet, and t is the time; X=(x, z) for ripple place is at two-dimensional space position coordinate, X_s=(x_s,z_s) it is two-dimensional space position, focus place coordinate, x and x_sIt is respectively ripple field and focus X-coordinate, z and z_sIt is respectively ripple field and focus ordinate zou;

3) with single big gun seismologic record as initial boundary condition, utilize following formula from the maximum record moment, just drill along time axle counter movement wave equation, obtain receiving ripple field:

$\frac{1}{v^2}\frac{{\∂}^2{P}_g(X,t)}{\∂t^2}-\mathrm{\Δ}{P}_g(X,t)=G(X_g,t);$

Wherein: P_g(X, t) is for receiving ripple field, G (X_g, t) it is single big gun seismologic record, X_g=(x_g,z_g) it is two-dimensional space position, wave-detector place coordinate, x_gFor wave-detector X-coordinate, z_gFor wave-detector ordinate zou;

4) when receiving ripple field backstepping, read mutually single big gun source Bo Chang in the same time, utilize following formula obtain waveform continuously after single big gun reverse-time migration imaging:

I_S(X)=S{��P_s(X,t)P_g(X, t) dt};

Wherein: S is for meeting second derivative continuous print smoothing operator;

5) all single big gun reverse-time migration imagings are carried out superposition, obtain waveform continuously after superposition reverse-time migration imaging.

2. method according to claim 1, feature is that the smoothing operator described in step 4) adopts cubic spline function interpolation smoothing operator.