CN102540254A

CN102540254A - Method for determining effective excitation region based on lighting analysis

Info

Publication number: CN102540254A
Application number: CN201010610724XA
Authority: CN
Inventors: 李培明; 蔡锡伟; 吴迪; 何宝庆
Original assignee: China National Petroleum Corp; BGP Inc
Current assignee: China National Petroleum Corp; BGP Inc
Priority date: 2010-12-29
Filing date: 2010-12-29
Publication date: 2012-07-04
Anticipated expiration: 2030-12-29
Also published as: CN102540254B

Abstract

The invention discloses a method for determining an effective excitation region in seismic exploration acquisition. The method comprises the following steps of: determining a lighting shadow region of a target body by using a wave equation lighting algorithm; placing a plane wave excitation source on a target horizon; obtaining a lighting intensity amplitude value for upward lighting at the shadow region on ground; normalizing and smoothing the lighting intensity amplitude value; determining the optimal ground surface excitation point distribution section; and increasing the number of the excitation points on the original basis according to an integral interval of a spacing to newly determine the effective excitation region. According to the method, the problem of way of rationally distributing the excitation points on a target stratum is solved by using seismic wave lighting analysis, rational distribution of the positions of the excitation points for seismic acquisition is facilitated, and the quality for original data of the seismic exploitation can be improved. The method is particularly suitable for complex target exploitation regions of salt dome structures, over-thrust nappe structures, igneous rocks and the like.

Description

A kind of method of confirming effective excitation area based on illumination analysis

Technical field

The present invention relates to geophysical exploration technology, is a kind of method of in seismic acquisition, confirming effective excitation area.

Background technology

In the seismic acquisition design; Utilize given recording geometry simulation field acquisition observation; Because the influence of factors such as the speed on stratum, inclination angle, structural feature; Can cause seismic event illumination intensity skewness spatially, illumination intensity is starkly lower than its zone of intensity on every side, or is called the illumination shadow region.

Obtain better stimulation effect in order to optimize shot point, improve the image quality of seismic data, to illumination shadow region or the bad zone of fixed imaging; And the weak objective interval of reflective information; Need according to a certain observed pattern, calculate and analyze the situation of a certain regional earthquake ripple illumination profile to given geological structure model; Carry out illumination analysis, reasonable geometry is confirmed in optimization according to the illumination intensity distribution situation.

Can only rely on collection in worksite technician's experience in the past, think that the location that can improve zone of interest imaging (generally all directly location above zone of interest) carried out shot point and encrypt or increase the method that receives spread length and improve stimulation effect.This method can't reach to zone of interest or objective body and effectively excite scope to lay, and is difficult to reach arrive improve zone of interest illumination result.

The analytical approach of the degree of covering of analysis purpose layer or the uniformity coefficient of geophone offset: the degree of covering of analysis purpose layer has dual mode now: a kind of is that the hypothesis underground medium is under the flat bedded situation, and trying to achieve is the degree of covering of common mid point bin (CMP); Another kind of situation is to have considered the influence of the horizontal change of subsurface interface, speed to raypath, therefore utilizes the ray tracing mode to ask for the degree of covering of common reflection point bin (CRP); Because the distribution situation of geophone offset can influence the analysis precision of speed, the energy and the phase characteristic of stack amplitude, so the uniformity coefficient analysis of geophone offset distribution also just becomes a kind of method of routine observation systematic analysis.

These methods all are just recording geometry itself to be done analysis, do not have really to be directed against amplitude or the energy that zone of interest can observe and analyze.

Summary of the invention

The object of the invention is to provide a kind of exploration target area or large-scale barrier that is directed against into aberration, the shot point position of rationally laying earthquake-capturing, and that optimizes that shot point lays scope confirms the method for effective excitation area based on illumination analysis.

The present invention realizes through following concrete topic step:

1) utilizes wave equation illumination algorithm, an above recording geometry is carried out the illumination profile that the seismic event illumination analysis obtains preparing construction area, confirm the illumination shadow region of objective body;

The illumination shadow region of the described definite objective body of step 1) or adopt known seismic section to confirm.

2) according to the scope in the illumination shadow region of zone of interest, the plane wave excitaton source is placed on this zone of interest position, upwards carries out the seismic event illumination, obtain the illumination intensity amplitude of shadow region up ligthing on ground;

3) according to following formula the illumination intensity amplitude of ground surface being carried out normalization handles:

B _i＝(A _i-A _min)/(A _max-A _min) (1)

In the formula, A _iBe the illumination amplitude that the i before the normalization is ordered, B _iBe the illumination amplitude that the i after the normalization is ordered, A _MinBe the illumination amplitude of minimum, A _MaxIllumination amplitude for maximum;

4) according to following formula data are carried out smoothing processing:

{\overset{&OverBar;}{A}}_{i} = Σ_{j = i - \frac{n}{2}}^{i + \frac{n}{2}} A_{j} / (n + 1) - - - (2)

In the formula,

The level and smooth back lighting amplitude of point; Level and smooth the counting of using of n-; A _jThe level and smooth front lit amplitude of-j point;

5) draw out level and smooth back lighting amplitude curve, determine best face of land shot point and lay section;

Step 5) is described, and to draw out level and smooth back lighting amplitude curve be that discrete normalized illumination intensity amplitude is carried out match and smoothly delineates out curve; 10 times of normalization illumination amplitude decay in curve; For effectively exciting the separatrix of scope; Landscape position on the separatrix is for the face of land shot point of the best is laid section.

Described illumination amplitude decays to 20dB.

6) according to the used recording geometry of step 1); According to step 5) select in face of land shot point is laid section; Integral multiple according to track pitch increases shot point quantity at interval on original basis; Reanalyse the variation of the illumination intensity of zone of interest according to step 1) to step 5), confirm effective excitation area again.

The described definite again effective excitation area of step 6); According to the used recording geometry of illumination, and the cautious sheet relation of arranging of big gun, seismic data obtained with the seismic event forward simulation; Seismic data before and after encrypting is carried out pre-stack time migration to be handled; The imaging of encrypting the front and back objective interval like shot point does not improve, and then the position of shot point encryption is unreasonable, needs definite effective excitation area.

The present invention utilizes the seismic event illumination analysis to solve problem how rationally to lay shot point to zone of interest, helps rationally laying the shot point position of earthquake-capturing, can improve the quality of seismic prospecting source book.The present invention is particularly suitable for salt dome structure, the contrary complex target exploration areas such as nappe structure, pyrogenic rock of covering.

Description of drawings

Fig. 1 is the velocity field model of exploration target area;

Fig. 2 is ground sheet lighting result;

Fig. 3 is target antidromic illumination result;

Fig. 4 is the normalization average amplitude distribution plan of antidromic illumination of the present invention on the face of land.

Embodiment

Specify the present invention below in conjunction with accompanying drawing.

Become aberration maybe can't observe the problem of underground a certain zone of interest to zone of interest, the present invention utilizes oppositely seismic wave means of illumination from weak illumination layer position, obtains the illumination intensity of objective interval on the face of land.The situation of change of base area sheet lighting smooth curve confirms effectively to excite scope again.

The present invention realizes through following concrete steps:

1) sets up the more accurate two-dimentional geology rate pattern in target area; Fig. 1 is the velocity field model of exploration target area, and solid black lines is the zone of interest that this area will study.At first should set up the more accurate velocity profile in this target area in order to carry out illumination analysis.

2) utilize wave equation illumination algorithm, carry out the seismic event illumination analysis, obtain preparing the illumination profile situation of construction area, confirm the illumination shadow region of objective body to preferred several kinds of recording geometrys (can be a certain recording geometry); Perhaps, need to confirm improved zone according to the seismic section in early stage.

Step 2) the illumination shadow region of described definite objective body or adopt known seismic section to confirm the shadow region.

Fig. 2 is after normally laying shot point according to a certain recording geometry; Illumination intensity reflection at the various objectives layer; Can confirm the weak illumination zone of this recording geometry like this, be exactly the weak illumination zone of this zone of interest position, district like the zone in the quilt circle among Fig. 2 ground sheet lighting result.

3) according to the scope in the illumination shadow region of zone of interest, the plane wave excitaton source is placed on this zone of interest position, upwards carries out the seismic event illumination, obtain the illumination intensity amplitude of shadow region up ligthing on ground; Extract the illumination value of ground surface by certain mesh spacing.

Fig. 3 is the illumination shadow region of from Fig. 2, confirming, utilizes plane wave excitaton source antidromic illumination method, upwards carries out illumination analysis, the illumination intensity that obtains.

4) according to following formula the illumination intensity amplitude of ground surface is carried out normalization and handle, obtain face of land normalization illumination amplitude.

B _i＝(A _i-A _min)/(A _max-A _min) (1)

5) to the illumination of the face of land normalization in step 4) amplitude data, data are carried out smoothing processing according to following formula, carry out smoothing processing after, obtain the face of land normalization amplitude that on average throws light on.

{\overset{&OverBar;}{A}}_{i} = Σ_{j = i - \frac{n}{2}}^{i + \frac{n}{2}} A_{j} / (n + 1) - - - (2)

In the formula, The level and smooth back lighting amplitude of point; Level and smooth the counting of using of n-; A _jThe level and smooth front lit amplitude of-j point;

6) draw out level and smooth back lighting amplitude curve, determine best face of land shot point and lay section;

Step 5) is described, and to draw out level and smooth back lighting amplitude curve be that discrete normalized illumination intensity amplitude is carried out match and smoothly delineates out curve; 10 times of normalization illumination amplitude decay in curve; Be that described illumination amplitude decays to 20dB; For effectively exciting the separatrix of scope, the landscape position on the separatrix is for the face of land shot point of the best is laid section.

7) according to step 2) used recording geometry; According to step 6) select in face of land shot point is laid section; Integral multiple according to track pitch increases shot point quantity at interval on original basis; According to step 2) reanalyse the variation of the illumination intensity of zone of interest to step 6), confirm effective excitation area again.

The described definite again effective excitation area of step 7); According to the used recording geometry of illumination, and the cautious sheet relation of arranging of big gun, seismic data obtained with the seismic event forward simulation; Seismic data before and after encrypting is carried out pre-stack time migration to be handled; The imaging of encrypting the front and back objective interval like shot point does not improve, and then the position of shot point encryption is unreasonable, needs definite effective excitation area.

Fig. 4 be with among Fig. 3 in the illumination intensity on the face of land, the illumination value distribution curve that obtains through normalization and smoothing processing.Through analytic curve confirm the face of land effectively excite scope, effectively exciting scope among the figure is that the position is between 22.5-24.14km.The zone that indicates with light color among Fig. 4 is exactly the weak illumination zone to Fig. 2, after the present invention analyzes, and the zone that should encrypt of gained.

Claims

1. confirm the method for effective excitation area based on illumination analysis for one kind, be characterized in realizing through following concrete steps:

B _i＝(A _i-A _min)/(A _max-A _min) (1)

4) according to following formula data are carried out smoothing processing:

{\overset{&OverBar;}{A}}_{i} = Σ_{j = i - \frac{n}{2}}^{i + \frac{n}{2}} A_{j} / (n + 1) - - - (2)

In the formula,

2. method according to claim 1, characteristics are illumination shadow regions of the described definite objective body of step 1) or adopt known seismic section to confirm.

3. method according to claim 1; Characteristics are that described to draw out level and smooth back lighting amplitude curve be that discrete normalized illumination intensity amplitude is carried out match and smoothly delineates out curve to step 5); 10 times of normalization illumination amplitude decay in curve; For effectively exciting the separatrix of scope, the landscape position on the separatrix is for the face of land shot point of the best is laid section.

4. method according to claim 1, the described illumination amplitude of claim 3 decays to 20dB.

5. method according to claim 1, characteristics are the described definite again effective excitation area of step 6), according to the used recording geometry of illumination; And the cautious sheet relation of arranging of big gun; Obtain seismic data with the seismic event forward simulation, the seismic data before and after encrypting is carried out pre-stack time migration handle, the imaging of objective interval does not improve before and after encrypting like shot point; Then the position of shot point encryption is unreasonable, needs to confirm effective excitation area.