CN102749644B - Pre-stack migration imaging method for obtaining optimal imaging effect based on searching reflecting interface normal angle - Google Patents
Pre-stack migration imaging method for obtaining optimal imaging effect based on searching reflecting interface normal angle Download PDFInfo
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Abstract
The invention discloses a pre-stack migration imaging method for obtaining an optimal imaging effect based on searching reflecting interface normal angle. The method includes that firstly a ray-tracing is performed from an O point to a series of common midpoints (CMP), angles of intersection, namely inclined angles, which are formed between a series of rays and perpendicular lines, are obtained from the O point, seismic data on the series of CMP gathers are subjected to a migration stack at the O point according to a range of different inclined angles to obtain stacked energy of different angles, migration stacked energy which corresponds to the series of angles is compared to find out an angle which can represent a maximum migration energy, the angle which can represent the maximum migration energy is determined as an interface binning normal angle F, the CMP of optimal migration stack image data is determined by the interface binning normal angle F, and the determined CMP gathers and the seismic data of the CMP gathers in a certain range nearby are applied to perform a pre-stack migration imaging at the O point. Compared with traditional pre-stack migration imaging methods, the method has the advantage that a clear image can be obtained.
Description
Technical field
The invention belongs to reflection shooting field, particularly relate to the geological data common midpoint position utilizing earthquake migration before stack road collection data determination reflecting interface normal corresponding, thus obtain the method for seismic migration image more clearly.
Background technology
Tectonic structure is carried out to the technology of imaging, more common is utilize reflection seismic migration before stack road collection data to carry out imaging, if underground medium is horizontal layer and isotropic, subsurface interface normal should perpendicular to level ground, and the common midpoint forming the geological data of optimal imaging figure is positioned at the subpoint of normal on ground.If but medium non-horizontal stratiform, namely interface if tilt, routinely, we do not know the common midpoint of the normal angle of interface point and the geological data of this optimized image of formation, so by likely this point formed reflection geological data all add up, and suppose that noise is random, obtain imaging results.But the method definitely can not understand subsurface interface normal angle and common geological data center position corresponding to reflection spot, so the data likely related to all are added up when superposing, and require that stacking fold is very large so that reduce noise, but the stacking fold of real data is limited, can not satisfy the demand in a lot of situation, these point reflection data inaccurate and non-of application speed reduce the resolution of imaging on the contrary in the superposition of this point.
Summary of the invention
In reflection shooting field, application migration before stack data determination subsurface reflective boundary normal, and then determine corresponding geological data common midpoint position, up to the present there is no effective method.And if in migration imaging process, understand the interface normal angle of subsurface imaging point, and then know the common midpoint forming the geological data of optimum stacking image at this point, just can carry out migration stack imaging to the geological data near this common midpoint specially, thus obtain the seismic section of high-resolution.
The present invention's CMP road collection data corresponding according to the interface normal angle of subsurface reflection point have the principle of maximum imaging amplitude, selected slant stack is carried out to data, only apply a small amount of earthquake data imaging, thus avoid because these point reflection data non-in a large number bring superposition noise in the superposition of this point and velocity deviation, thus the disadvantage that resolution reduces.
As shown in Figure 1,1 O on the tiltedinterface of underground, carries out imaging job by two geological data group CMP1 and CMP2.CMP1 road collection data form S1-R1, S2-R2 by big gun is cautious, and wherein S1, S2 representative is blown out a little, and RI, R2 represent geophone station.Obviously, CMP1 road collection data can not form good picture at O point, and reason is that S1-R1 and S2-R2 point does not all have effective high amplitude reflection at O point, and the line of CMP1 and O point is not the normal of interface at O point.On the contrary, because the line of CMP2 and O point is the normal of interface at O point, the big gun of CMP2-examine forming complete catoptric system around normal, so CMP2 road collection data can form good picture at O point.If in imaging process, we abandon CPM1 data and CMP2 data are picked out independent imaging, and imaging precision will improve greatly, thus avoid the problem of the resolution reduction that a large amount of non-O point reflection data investigation brings.If underground can be divided into limited unit of boundary, the same according to CMP2 to unit of each boundary, find its normal, obtain the complete catoptric system around normal, and according to this road collection data imaging respectively, just can obtain the image of high-precision whole underground medium.
In concrete detection, the pattern taked is:
Suppose the medium of the slow change that underground medium is isotropy, speed is V, shot point S(xs) and geophone station R(xr) be positioned at ground, subsurface reflection point O(x, z) normal direction of residing interface bin is F(Fig. 2).Wherein incident angle Ф refers to the angle of incident wave and normal; t
0for O point is to the two-way time on ground.V and t
0for experiment can obtain data.
As shown in Figure 2, according to DSR equation, α angle and β angle can be obtained [1] by following formula, namely
With
In theory, incident angle Φ should be two angular average, namely
Φ＝(-α-β)/2， ……(3)
As shown in the figure, normal angle F is
F=α+Ф ……(4)
In uniform dielectric situation, α angle and the β angle of (1) and (2) formula can be calculated by following formula,
With
At actual seismic Data processing, real F angle and Φ angle are difficult to obtain, only when the signal source in certain moment that knows for sure is reflected from this bin exactly, and obtaining of ability uniqueness, and this situation almost cannot.
But we know, only when the F angle that (4) formula of application obtains is consistent with the true normal of subsurface interface bin, the reflection amplitude of this point is maximum, and the energy that migration stack obtains is the strongest.Thus, a feasible scheme does ray tracing from a series of CMP point to O point, obtains a series of angle at O point; Again the geological data on a series of CMP roads collection is carried out migration stack separately at this point, obtain a series of picture energy after skew; The migration stack energy size that relatively series of angles is corresponding, finds the angle representing peak excursion energy, confirms that this angle is interface panel method line angle F.Meanwhile, we also can know, cause the CMP of the geological data of peak excursion stack power point to be the geological data common midpoint formed corresponding to optimized migration stacking image.
Concrete steps are:
(1) first do ray tracing from O point to a series of CMP point, obtain the angle of cut of a series of ray and perpendicular line at O point, i.e. inclination angle;
(2) again the geological data on this serial CMP road collection is pressed different angle scope at O and carry out migration stack, obtain the stack power of different angles;
(3) compare the migration stack energy size that series of angles is corresponding, find the angle representing peak excursion energy, confirm that this angle is interface panel method line angle F;
(4) the common midpoint CMP of the data of optimized migration superimposed image is determined by the normal angle F of interface bin;
(5) the CMP Dao Ji that determines of criteria in application step (4) and around it in certain limit the geological data of road collection carry out prestack migration image at O point.
Conventional Kirchhoff pre-stack time migration does not apply information when ray-tracing scheme obtains, and therefore, utilizes ray tracing and scanning to estimate that the F angle obtained just is bordering on luxury.Generalized case, if underground medium is bordering on smooth and isotropy, as approximate, the scanning at F angle estimates that the line that can directly utilize CMP to O to put is similar to realization, that is
Fig. 3 is the actual example utilizing two-dimension earthquake offset data to scan normal angle.Figure left side is migration stack section, at 2700-2800 millisecond place, pendage angle is approximately 35 degree, by the geological data on ground in units of CMP is carried out migration stack at subsurface imaging point, and forming method line angle gathers (right part of flg in Fig. 3, horizontal ordinate is angle, ordinate is the time) after, can see, the migration stack concentration of energy on right side is between 25-45 degree at normal angle, the just in time degree of tilt on corresponding stratum.Energy scan is carried out to right side data in figure, corresponding about 35 degree of ceiling capacity.The normal angle of this explanatorily bed interface completely can by obtaining the scanning process of angular stack road collection data capacity.
If find the normal angle of interface bin and the common midpoint CMP determining the data that can form optimized migration superimposed image, optionally select data and carry out prestack migration image, the resolution of imaging section will improve greatly, thus realize focusing on stacking image.On CMP road collection, shot point and geophone station are plane geometry symmetries to CMP point.Under isotropy uniform dielectric supposed premise, the reflection wave of subsurface imaging point only just has record on the CMP position of interface normal direction indication, and other CMP point, owing to can't accept the reflection of this point, does not have reflection record.But according to Fresnel wave theory, also should possess the condition accepting reflection wave around the data common midpoint CMP position of this normal angle indication, different from CMP point, what their accepted is the more weak seismic event that can be described as diffraction of energy.Therefore, the scope (Fig. 4) that application Fresnell first zone of reflections surrounds, shadow region is wherein that Fresnell is with scope, and W is superposition power.Geological data is weighted migration stack, and application Gauss weight coefficient, can obtain subsurface interface bin optimized migration-focal imaging achievement.
The scope of migration stack can be applied Fresnell band and define, and also can otherwise define.If underground medium reflecting surface is level, defining of this scope is equivalent to defining of migration aperture size.
In order to process the convenience of problem, in actual shifts process, after scanning obtains normal F angle, directly can apply the front and back tolerance △ F at F angle to define superposition scope, namely
F
min＝F-ΔF ……(8)
With
F
max＝F-ΔF ……(9)
Wherein:
Fmin is the minimum normal angle participating in superposition;
Fmax is the maximum normal angle participating in superposing.
Focusing superposition is carried out to geological data, means:
Wherein:
The picture that Image (0) is underground O point; SF is the superposition transforms of certain CMP data corresponding at this point, and the normal angle that this CMP and O puts is F; WF is superposition weight coefficient.
Above-mentioned geological data is weighted migration stack, subsurface interface bin optimized migration-focal imaging achievement can be obtained.
If geological data three-dimensional data, the selection at F angle also will be carried out in different azimuth, that is will select F angle in different azimuth angular region, then carries out above-mentioned migration stack imaging.
Accompanying drawing explanation
Fig. 1 is earthquake CMP road collection data and subsurface reflective face graph of a relation.
Fig. 2 is interface bin normal and shot point and acceptance point geometric relationship figure.
Fig. 3 is that prestack migration profile and normal angle gathers data relationship illustrate.
Fig. 4 is the migration stack schematic diagram of reflectance data at imaging point.
Fig. 5 is that application routine techniques (left side) and application technology of the present invention (right side) carry out imaging results comparison diagram to geological data.
Fig. 6 is that the technology of the present invention is applied to imaging section that pre-stack time migration obtains and the comparison diagram of imaging section that conventional pre-stack time migration obtains.
Fig. 7 is the seismic reflection imaging section figure that the pre-stack time migration formation method of certain research institute domestic application routine obtains.
The pre-stack time migration imaging processing comparison diagram that the software that Fig. 8 applies this technological development carries out Fig. 7 geological data.
Embodiment 1
Application the inventive method, we have carried out imaging processing to somewhere geological data, obtain good imaging effect.Show the final migration imaging section achievement that the conventional prestack time migration technique of application obtains on the left of Fig. 5, right side shows the pre-stack time migration imaging achievement section that application the present invention obtains.Can find out, the seismic image that application the present invention obtains has higher resolution, and skew noise is obviously less, and frequency significantly improves, and particularly the substratum of large cover ground interlayer is clear and legible.
Embodiment 2
Lower Fig. 6 geological data derives from certain Volcanic area, and signal to noise ratio (S/N ratio) is medium, but after migration stack, lineups continuity is undesirable.Analyzing reason is that part interference wave energy is comparatively strong, because degree of covering is few in migration process, so the superposition decay of noise is undesirable; For this reason, application the technology of the present invention, after obtaining imaging point interface panel method line angle, the geological data common midpoint CMP corresponding to normal angle and surrounding some somes geological datas carry out the imaging of selectivity weighted stacking, obtain good more high-resolution prestack migration image section.Fig. 6 left-side images application conventional stacking offset method, image right applies the prestack time migration method that technology of the present invention is carried out.Relatively both sides image, new technology improves the resolution of migrated section really, makes image more clear, and lineups are continuous, and integral image noise level also reduces many.
Embodiment 3
Certain seismic data process project, requires to carry out Precise imaging process to geological data, tomography and stratigraphic resolution clear.Before this, certain research institute domestic once carried out fine processing to these data, did not reach the requirement of Party A.We after data characteristics, think that imaging technique newly developed has the ability to reach the requirement of Party A in serious analysis, so the imaging software of application the art of this patent exploitation has carried out imaging processing to these data.
Fig. 7 is that certain research unit domestic is to this geological data imaging results.In figure visible major faults and stratum all more clear, but stratum, particularly shallow structure comparatively around the structure of details and main structure are a bit fuzzy, seem to think the flat sleeping principal fault of existence one direct by stratum bad break in explanation.Fig. 8 is the imaging processing result that the technical software of our exploitation of application carries out these data.Visible main structure is substantially identical with Fig. 7, but fine texture has had very large change, the tomography controlling the growth of local area upper formation does not become the large-scale tomography of stratum bad break thus impels top growth to be a large-scale slippage body, and it in fact still can be interpreted as the core portion of a Huge Recumbent Folds.This process achievement obtains the abundant affirmation of Party A, for we strive honor, also for the application of this technology provides the support of strong market.
Claims (2)
1., based on the prestack migration image method of searching reflecting interface normal angle acquisition optimal imaging effect, it is characterized in that comprising following steps:
(1) first do ray tracing from O point to a series of CMP point, obtain the angle of cut of a series of ray and perpendicular line at O point, i.e. inclination angle;
(2) again the geological data on this serial CMP road collection is pressed different angle scope at O and carry out migration stack, obtain the stack power of different angles;
(3) the migration stack energy size that series of angles is corresponding is compared, find the angle representing peak excursion energy, confirm that this angle is interface panel method line angle F, under underground medium is bordering on smooth and assumption of isotropy situation, the line that normal angle F directly utilizes CMP to O to put is similar to realization, that is
(4) the common midpoint CMP of the data of optimized migration superimposed image is determined by the normal angle F of interface bin;
(5) the CMP Dao Ji that determines of criteria in application step (4) and around it in certain limit the geological data of road collection carry out prestack migration image at O point;
Migration stack imaging will be weighted by the data obtained application gaussian coefficient within the scope of step (4) and (5) middle Fresnell first zone of reflections; Will before and after normal angle F in step (4) and (5) in certain limit △ F the data obtained be weighted migration stack imaging.
2. according to claim 1 based on the prestack migration image method of searching reflecting interface normal angle acquisition optimal imaging effect, it is characterized in that step (4) and (5) if in geological data three-dimensional data, the selection at F angle also will be carried out in different azimuth, that is will select F angle in different azimuth angular region.
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