阅读说明：本技术 基于不规则模型孔径的共偏移距Kirchhoff叠前深度偏移成像方法 (Common offset Kirchhoff prestack depth migration imaging method based on irregular model aperture ) 是由 孙章庆 韩复兴 刘明忱 于 2019-10-10 设计创作，主要内容包括：本发明涉及一种基于不规则模型孔径的共偏移距Kirchhoff叠前深度偏移成像方法,针对常规矩形孔径存在的的宽度太小虽能压制浅层偏移噪声,但会降低深部成像质量,太大虽能保证深部成像效果,但会引入更强偏移噪声而降低浅部成像质量等问题,综合考虑偏移距大小和成像模型空间的最大深度,设计一种浅部窄深部宽的不规则模型空间偏移孔径,并采用不等距网格剖分该不规则孔径和仅在不规则模型孔径中计算走时表,再实施共偏移距域Kirchhoff叠前深度偏移成像。该方法能有效压制浅层偏移噪声并保证深部成像质量,因不需计算不规则孔径外的走时表而能提高计算效率,在不过多增加计算量的前提下尽可能的提高深层偏移孔径的范围,进而提高深部甚至是超深部成像质量等优势。(The invention relates to a common offset Kirchhoff prestack depth migration imaging method based on irregular model apertures, which aims at the problems that although the width of a conventional rectangular aperture is too small, shallow layer migration noise can be suppressed, deep portion imaging quality can be reduced, and although the width of the conventional rectangular aperture is too large, deep portion imaging effect can be guaranteed, stronger migration noise can be introduced, shallow portion imaging quality is reduced and the like. The method can effectively suppress shallow layer offset noise and ensure deep imaging quality, can improve the calculation efficiency because a travel time table outside the irregular aperture is not required to be calculated, and can improve the range of the deep layer offset aperture as much as possible on the premise of not increasing the calculation amount so as to improve the deep and even ultra-deep imaging quality and the like.)

1. A common offset distance Kirchoff prestack depth offset imaging method based on irregular model apertures is characterized by comprising the following steps:

a. reading in known conditions: the method comprises the steps of acquiring common offset seismic data, observing systems, offset parameters and offset velocity model information;

b. according to the known conditions read in the step a, firstly, according to a conventional offset aperture selection method, according to the offset distance size 2d, a rectangular offset aperture with the width of 2L and the depth of the rectangular offset aperture being the maximum depth H of the imaging model space is constructed, and then a part with the depth of less than H (x) is removed from the rectangular aperture, wherein: the expression for h (x) is the following piecewise function:

an irregular offset aperture in model space can be generated that is shallow, narrow and deep, wherein: when the piecewise function h (x) is constructed, the established local rectangular coordinate system takes a midpoint O between the shot point S and the receiving point R as the origin of coordinates,

c. b, according to the offset parameters input in the step a, namely the grid spacing of the imaging space, adopting irregular offset apertures in the unequal mesh subdivision model space, and assigning offset speed values and initialized imaging values on grid nodes;

d. in the unequal distance grid in the step c, all shot-geophone points of a certain common offset gather are respectively used as seismic source points, and a ray tracing method is adopted to calculate a travel-time table required by offset imaging of all gathers in the common offset gather;

e. on the basis of the step d, a Kirchhoff prestack depth migration method is adopted, and in the irregular migration aperture grid in the step c, migration imaging is carried out on the common migration distance gather to obtain an imaging value of the common migration distance gather;

f. repeating the steps b-e for all common offset gathers: respectively generating corresponding irregular offset apertures, subdividing the irregular apertures by adopting an unequal mesh, calculating a travel time table in the irregular apertures, implementing Kirchhoff offset, then superposing and summing to obtain a final imaging result, and outputting a final offset imaging value in a model space.

Technical Field

The invention belongs to the technical field of geophysical seismic data processing, particularly relates to a seismic migration imaging method, and particularly relates to a common offset Kirchhoff prestack depth migration imaging method based on irregular model apertures for the problem of migration apertures in migration imaging.

Background

Due to the advantages of high calculation efficiency, stable imaging quality, inaccurate low sensitivity of a velocity model, easiness in implementation of migration velocity analysis and the like, the common offset Kirchhoff prestack depth migration imaging method is still a seismic imaging method mainly and mainly adopted in the oil and gas exploration field in the oil industry at present. The imaging quality of the conventional co-offset Kirchhoff prestack depth-shift imaging method is governed by a number of factors, of which the shift aperture is one of the most important. How to design reasonable aperture range and form directly determines the characteristics of the offset method such as imaging quality, calculation efficiency, offset noise suppression and the like. In view of this, a seismic migration imaging method needs to be designed to specifically address the migration aperture problem in the model space of the common offset Kirchhoff prestack depth migration imaging method.

Regarding the problem of the migration aperture, the 'formation dip angle constraint adaptive aperture prestack time migration' of Liu and year and the like is disclosed in the 'oil geophysical exploration' 2014 05, and the classic rectangular migration aperture formula is corrected by using the formation dip angle, so that the rectangular migration aperture with an ideal imaging effect is determined; in 2016 03 of petroleum geophysical exploration, Chenshide and the like, the optimization of the aperture of a dip angle gather for absorbing and compensating prestack time migration by viscous media is disclosed, and the concept of the optimal migration aperture is provided in the article, wherein the concept of the optimal migration aperture is that the time difference and amplitude change of the gather are obvious on two sides of a homophasic axis by taking a stationary phase point as the center, the vertex of the concentrated bending of the homophasic axis is the stationary phase point, and the nearly straight part of the homophasic axis in the neighborhood of the stationary phase point is the optimal migration aperture; petroleum geophysical prospecting, 03 in 2017, discloses "dip angle domain adaptive aperture prestack time migration" of wujiloy, et al, which proposes a method for adaptively determining a migration aperture according to a stratigraphic dip angle; the geophysical progress, 2018, discloses a 'phase-stabilized efficient viscoelastic prestack time migration method and application' of Junihong, which proposes that a uniform migration aperture cannot meet imaging quality requirements, and the migration aperture needs to consider the change problem of a model space velocity medium; the 'university of northeast China' journal of Petroleum 'in 2019, 03, discloses a Kirchhoff time optimal migration aperture based on a two-step scanning method' of Lixueli and the like, and the Kirchhoff time optimal migration aperture is researched by the aid of the two-step scanning method, influences of imaging inclination angles and seismic wave main frequencies on Fresnel zones are further determined in a self-adaptive mode, and a data driving determination method of the optimal migration aperture is established based on the imaging inclination angles and the Fresnel zones. The studies described above have conducted intensive studies on the migration aperture, highlighting the importance of the migration aperture, but they are directed to all prestack time migration methods.

The prestack depth migration method has higher imaging quality and is more easily adapted to complex media, and a uniform and single migration aperture is adopted at present. Typically the offset aperture may be full space, i.e. single shot data, with each corresponding pass imaging all imaging points in the subsurface imaging space. In practice, this full aperture imaging introduces much unwanted offset noise, which significantly increases the amount of computation. In addition, the model space also adopts a rectangular offset aperture, namely, when the offset algorithm is used for calculating the imaging value of the underground point, only a rectangular area between the shot point and the receiving point is calculated, and the processing mode can greatly suppress offset noise. If the rectangular offset aperture is too narrow, shallow offset noise can be greatly suppressed to obtain a better shallow imaging effect, but the imaging quality is poor due to insufficient energy information participating in offset calculation in a deep layer; if the width is too wide, the imaging quality of the deep layer is better, but the imaging quality of the shallow layer is seriously reduced due to a large amount of offset noise introduced during imaging. Especially, when the data quality is not ideal, the imaging quality of the offset aperture determination mode of the 'one-knife-cut' type is more difficult to guarantee. In practice, when making the offset aperture determination, the following core issues need to be considered: how to design an excursion aperture, can suppress the excursion noise and improve shallow portion imaging quality in the shallow layer, can enlarge effective signal source and better assurance deep portion imaging quality in the deep layer, can also compromise imaging quality and imaging efficiency simultaneously.

In order to solve the problems, a novel prestack depth migration imaging method needs to be developed, so that seismic data can obtain a clearer imaging effect when Kirchhoff migration imaging is carried out, and imaging efficiency is considered while imaging noise is suppressed.

Disclosure of Invention

The invention aims to provide a common offset Kirchhoff prestack depth migration imaging method based on an irregular model aperture, aiming at the problems that a large amount of migration noise is introduced or effective signals are lost in a large amount of wide or narrow rectangular apertures, and shallow and deep imaging quality, imaging efficiency and migration noise suppression cannot be considered.

The purpose of the invention is realized by the following technical scheme and steps:

a common offset Kirchoff prestack depth offset imaging method based on irregular model apertures comprises the following steps:

a. reading in information such as common offset seismic data, an observation system, an offset parameter, an offset velocity model and the like, which form known conditions of the method;

b. according to the known conditions read in the step a, firstly, based on a conventional offset aperture selection method, according to the offset distance size 2d, a rectangular offset aperture with the width of 2L and the depth of the rectangular offset aperture being the maximum depth H of the imaging model space is constructed, and then a part with the depth less than H (x) is removed from the rectangular aperture (wherein the expression of H (x) is the following piecewise function:

an irregular offset aperture in model space can be generated that is shallow, narrow and deep, wherein: when the piecewise function h (x) is constructed, the established local rectangular coordinate system takes a midpoint O between the shot point S and the receiving point R as the origin of coordinates,

the direction is positive direction of x-axis, the direction of increasing depth is positive direction of h-axis, r is curvature radius of smooth continuous curve of irregular boundary of pore diameter, and at the same time, it is ensured that the pore diameter is gradually widened along with the increase of depth and smoothly transited to maximum width of rectangular pore diameterDegree 2L, here it needs to be defined: r is less than or equal to H, L and is less than or equal to (r + d);

c. according to the offset parameters (grid spacing of an imaging space) input in the step a, adopting irregular offset apertures in an unequal mesh generation model space, and assigning offset speed values and initialized imaging values on grid nodes;

d. in the unequal distance grid in the step c, all shot-geophone points of a certain common offset gather are respectively used as seismic source points, and a ray tracing method is adopted to calculate a travel-time table required by offset imaging of all gathers in the common offset gather;

e. on the basis of the step d, a Kirchhoff prestack depth migration method is adopted, and in the irregular migration aperture grid in the step c, migration imaging is carried out on the common migration distance gather to obtain an imaging value of the common migration distance gather;

f. repeating the steps b-e for all common offset gathers: respectively generating corresponding irregular offset apertures, subdividing the irregular apertures by adopting an unequal mesh, calculating a travel time table in the irregular apertures, implementing Kirchhoff offset, then superposing and summing to obtain a final imaging result, and outputting a final offset imaging value in a model space.

Compared with the prior art, the invention has the beneficial effects that:

1. the irregular offset aperture with the shallow part, the narrow part and the wide part designed by the invention can suppress offset noise in the shallow layer to improve the imaging quality of the shallow part, and can enlarge effective signal sources in the deep layer to better ensure the imaging quality of the deep part, thereby comprehensively achieving the purpose of giving consideration to both the imaging quality of the shallow part and the imaging quality of the deep part;

2. the travel time table of a calculation area outside the irregular model aperture boundary needs to be calculated, so that the calculation efficiency of the migration algorithm is greatly improved, and the purpose of considering both the imaging quality and the imaging efficiency is further achieved;

3. based on the advantages of the two aspects, when the offset aperture is designed, the deep imaging aperture range can be improved as much as possible, and further the imaging quality of a deep layer and even an ultra-deep layer is ensured on the premise of not increasing the calculated amount too much.

Drawings

FIG. 1 is an overall flow chart of the present invention of a common offset Kirchoff prestack depth migration imaging method based on irregular model aperture;

FIG. 2 is a schematic diagram of an implementation of establishing an irregular aperture;

FIG. 3a images a spatial offset velocity model;

FIG. 3b co-offset seismic data;

FIGS. 4 a-4 d illustrate different shapes of offset apertures used in the implementation of the example imaging contrast analysis, FIG. 4a rectangular offset aperture with full model space, FIG. 4b a rectangular aperture with a width of 2.0km, FIG. 4c a rectangular aperture with a width of 1.0km, FIG. 4d an irregular offset aperture according to the present invention;

FIG. 5a uses full model space rectangular offset aperture imaging results;

FIG. 5b imaging results using a rectangular aperture with a width of 2.0 km;

FIG. 5c imaging results using a rectangular aperture with a width of 1.0 km;

FIG. 5d imaging results with irregular offset apertures;

FIG. 6 is a detailed diagram of an example implementation of an overall flow chart of the method of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

The invention can suppress shallow layer offset noise when the width of the conventional rectangular aperture is too small, but can greatly reduce the deep imaging quality; the too large aperture width can guarantee the deep imaging effect, but can introduce stronger skew noise and then reduce shallow portion imaging quality scheduling problem. Comprehensively considering the offset distance and the maximum depth of an imaging model space, providing an irregular model space offset aperture with a shallow part, a narrow part and a deep part, subdividing the irregular aperture by adopting an unequal mesh, calculating a travel time table only in the irregular model aperture, and then implementing Kirchhoff prestack depth offset imaging with a common offset distance domain, comprising the following steps of:

a. reading in information such as common offset seismic data, an observation system, an offset parameter, an offset velocity model and the like, which form known conditions of the method;

b. according to the known conditions read in step a, as shown in fig. 2: firstly, based on a conventional offset aperture selection method, according to the offset distance size 2d, constructing a rectangular offset aperture with the width of 2L and the depth of the rectangular offset aperture as the maximum depth H of an imaging model space, and then removing a part with the depth less than H (x) (wherein the expression of H (x) is the following piecewise function:

an irregular offset aperture in model space can be generated that is shallow, narrow and deep, wherein: when the piecewise function h (x) is constructed, the established local rectangular coordinate system takes a midpoint O between the shot point S and the receiving point R as the origin of coordinates,

the direction is the positive direction of x axle, and the direction that increases to secret degree of depth is the positive direction of h axle, and r is the radius of curvature of the smooth continuous curve that is the irregular border of pore diameter, in order to guarantee that the aperture widens gradually and smooth transition to the maximum width 2L of rectangle aperture along with the increase of depth simultaneously, here needs to be injectd: r is less than or equal to H, L and is less than or equal to (r + d);

c. according to the offset parameters (grid spacing of an imaging space) input in the step a, adopting irregular offset apertures in an unequal mesh generation model space, and assigning offset speed values and initialized imaging values on grid nodes;

d. in the unequal distance grid in the step c, all shot-geophone points of a certain common offset gather are respectively used as seismic source points, and a ray tracing method is adopted to calculate a travel-time table required by offset imaging of all gathers in the common offset gather;

e. on the basis of the step d, a Kirchhoff prestack depth migration method is adopted, and in the irregular migration aperture grid in the step c, migration imaging is carried out on the common migration distance gather to obtain an imaging value of the common migration distance gather;

f. repeating the steps b-e for all common offset gathers: respectively generating corresponding irregular offset apertures, subdividing the irregular apertures by adopting an unequal mesh, calculating a travel time table in the irregular apertures, implementing Kirchhoff offset, then superposing and summing to obtain a final imaging result, and outputting a final offset imaging value in a model space.

To better illustrate the effects of the above embodiments, a specific example is given below: