CN102495427A - Interface perception ray tracing method based on implicit model expression - Google Patents
Interface perception ray tracing method based on implicit model expression Download PDFInfo
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Abstract
The invention discloses an interface perception ray tracing method based on implicit model expression and is applicable to a system for inverting, modeling and offsetting seismic data. The method comprises the following steps of: expressing a geological interface based on an implicit function; describing a formation depositional sequence by using a binary tree, and generating a three-dimensional geologic body construction model by using the geological interface which is implicitly expressed; on the basis of an implicitly-expressed construction model, assigning speed values to vertexes of a tetrahedron unit which is included in a formation body or intersected with a formation surface according to an appointed speed distribution rule of each formation body, and organizing and storing speed files by taking the formation body as a unit; and under the constraint of the implicitly-expressed construction model, performing ray tracing based on interface perception in the construction model in a segmented iteration mode according to a kinematical equation and a reflection law. The method has the advantages that: a complicated geological construction model can be subjected to automatic velocity modeling; high-accuracy and powerful ray tracing is realized; and important parameters are provided for seismic inversion, offset imaging and numerical simulation.
Description
Technical field
The present invention relates to a kind of geological structure model constraint in implied expression down, carry out the System and method for of speed modeling and ray tracing automatically, particularly a kind of interface perception ray-tracing scheme based on the implicit model expression.
Background technology
Because ray is carrying in a large number for seismic inversion, modeling and skew Useful Information very, so ray-tracing scheme is being played the part of very important role in seismic exploration data is handled.If underground speed is known, parameters such as raypath, whilst on tour, amplitude and emergence angle can obtain through the numerical evaluation of ray tracing.
Just proposed ray-tracing scheme as far back as people such as Cerveny in 1977, Cerveny afterwards and Hron have carried out again replenishing and are perfect, and it is theoretical that these have constituted classical ray tracing.Ray tracing is also very direct from the mathematical theory to the computer realization; But up in recent years; Three-dimensional ray tracing is also very limited at actual seismic inversion and Application in Modeling; Be that scientific research field carries out simulative example research mostly, for example generate three-dimensional theogram, or check certain hypothesis and approximate rationality in order to test new disposal route.So the major reason that this method can not be widely used at petroleum industrial circle, using for real complex geological structure zone 3-d seismic exploration is to expend very much computational resource, and the error of classic method also is very big.Existing many speed modeling methods based on grid are used for ray tracing and tomographic inversion both at home and abroad.Chapman had also introduced a kind of speed modeling algorithm based on ray in 2004, can perception aspect framework, and can be when ray runs into aspect along the ray propagates physical attribute.But these classic methods are usually based on tetrahedral grid, and the generation of grid is retrained by section and aspect, comprises unconformability and overlying strata etc., and in the area of complicated underground structure, often very difficulty and generating mesh are of low quality in the grid generation.2006; People such as Ruger propose a kind of method that from the even speed grid of meticulous sampling, generates the formation velocity structured grid automatically; This method need not the constraint information (like tomography and stratum) that provides extra; The speed grid is embedded in the tetrahedral grid of Delaunay segmentation at discontinuity zone, but they fundamentally do not solve the difficult problem that the constraint grid generates.Traditional ray tracing is divided into several different stages with workflow usually: pick up structural attitude, formation speed model and ray tracing; Except the input of output meeting of previous stage as next stage; Each stage is often separate, does not have other positive connection.
The invention discloses a kind of interface perception ray-tracing scheme of expressing based on implicit model; Three Main Stage of ray tracing: structure modeling, speed modeling and ray tracing have the unified method basis---the implied expression method; Can not only the effective expression complex geological structure, and each stage organic connections, except that being the last period the input of the latter half; Also, constitute a unified integral body for the latter half provides support structure and computing method to support.
Summary of the invention
The technical matters that the present invention will solve is: the method for speed modeling and high precision ray tracing is carried out in research automatically in the complex geological structure model; The system that is used for seismic exploration data inverting, modeling and skew; Solving the problem of existing ray-tracing scheme performance difficulty in complex geological structure, thereby overcome the difficulty that precision is not high in the prior art, efficient is lower and be difficult to effectively support seismic inversion, skew and simulation.
The present invention solves the technical scheme that its technical matters takes: a kind of interface perception ray-tracing scheme of expressing based on implicit model is provided; It is under the tectonic model constraint that implicit model is expressed; Carry out speed modeling and interface perception ray tracing, may further comprise the steps:
Steps A, geological interface and geologic body generation method construct three-dimensional geologic structure model based on implicit expression comprise symbolic distance field and stratum binary tree;
Step B, automatic desin speed model on the three-dimensional structure model basis of implied expression;
Step C carries out ray tracing according to tectonic model and rate pattern.
Symbolic distance field in the steps A is the implied expression form of tectonic model, and the zero contour surface of symbolic distance field is in order to expression corresponding geological aspect; The stratum binary tree is a data structure of describing geology aspect and geologic body spatial topotaxy, and have following character: each non-leaf node is represented an aspect, the area of space that each leaf node representative aspect is cut apart, i.e. stratum body; Main stratum is the father or the ancestor node on respective secondary stratum always; To arbitrary stratum binary tree node, its left sibling, oneself, its corresponding aspect of right node that always becomes sequence or reverse sequence arranges.
Step B further comprises:
Step B1; According to stratum binary tree and symbolic distance field is that each stratum body is specified tetrahedral grid; These tetrahedral grids comprise and are positioned at stratum body tetrahedral grid inner and that intersect with stratum body outland aspect fully, crossing tetrahedral grid with its Different Strata body that intersects in respectively preserve a duplicate;
Step B2 is that velocity amplitude is composed on the tetrahedral grid summit of each stratum body appointment according to the speed create-rule, and is unit organization speed file with the stratum body; Speed generates rule and is determined jointly by stratal surface base velocity function and velocity gradient, and wherein velocity gradient derives from sand smeller and geophysicist's priori or obtained by migration velocity analysis.
Step C further comprises:
Step C1 according to kinematical equation, adopts the method for cutting apart when waiting, and the raypath segmentation is calculated; Each calculates segmentation and is called a ray step, and to each ray step, if itself and the border triangle intersect of tetrahedron element, it will be blocked by this face so, and joining becomes this ray and goes on foot new terminal point.
Step C2, whether the inspection ray step intersects with tomography: express because fault surface adopts the tetrahedral grid face to show, and cancelled tomography both sides tetrahedron topological adjacency relation; The adjacent tetrahedron of sharing fault surface keeps a common sides duplicate separately; When ray step and tetrahedral border triangle intersect, check whether this face is fault surface, if; Then this ray step terminal point is labeled as and is positioned at tomography, promptly this ray step intersects with tomography;
Step C3; Whether the inspection ray step intersects with stratal surface; Because stratal surface has adopted the latent function that shows to express; Can not directly judge crossingly, can use the rule of judging spatial point layer position in the binary tree of stratum, to confirm:, can confirm that this ray step is positioned at certain stratum body fully and does not have with stratal surface crossing if starting point and the terminal point in ray step are positioned at the same leaf node of stratum binary tree; Otherwise this ray step intersects with a stratal surface at least.Further confirm the definite position of intersection point: each node on checking from this stratum, ray step starting point place body leaf node to the ancestral path of tracing back of root node; For nonleaf node; If starting point and terminal point opposite in sign in the symbolic distance field in ray step; Can confirm that then ray step and this stratal surface intersect, the starting point in ray step and the ratio of the value of terminal point in the symbolic distance field can be confirmed the definite position of intersection point.
Reflection and refraction when the ray step intersects with tomography or stratum, will take place in step C4, use the symbolic distance field, can calculate the normal vector at ray and aspect joining place rapidly, with convenient ray incident angle and the emergence angle calculated.When the ray step intersected at tomography, the reflected ray step still carried out in the current tetrahedron of current stratum body, but has new directions of rays; Refracted rays step will carry out sharing in the adjacent tetrahedron of fault surface with current tetrahedron; Can confirm stratum, new tetrahedron place body according to the rule of judging spatial point layer position; If body not on current stratum; Need to load corresponding stratum body speed file, and use the speed create-rule of new stratum body to go on foot point interpolation to go out velocity amplitude as refracted rays.When the ray step intersected at the stratum, the reflected ray step still carried out in the body of current stratum, but has new directions of rays; The refracted rays step will originate in new stratum body, and new stratum body uses the rule of the judgement spatial point layer position of revising to confirm, and loads corresponding stratum body speed file, uses new tetrahedron duplicate to go on foot point interpolation as refracted rays and goes out velocity amplitude.
The rule of the judgement spatial point layer position among step C3 and the C4 is meant: the binary tree root node begins the selectivity traversal from the stratum; Go out the value of given spatial point by interpolation in the symbolic distance field of the corresponding aspect of current binary tree node; The next child node that travels through of symbol decision by this value is left child node or right child node; So continue traversal, promptly provided layer position, spatial point place until arriving at leaf node; Being meant of the rule of the judgement spatial point layer position of revising: when the nonleaf node of traversal to crossing stratum, if current stratum body is positioned at left subtree, then continue traversal from right subtree, vice versa.
The advantage that the present invention is compared with prior art had is:
1, the present invention can directly serve speed modeling and ray tracing because the implicit method that adopts is expressed tectonic model, is applicable to the complex geological structure environment;
2, in the speed modeling of the present invention; Adopting multiple duplicate method, is unit formation speed file with the stratum body, can embed sand smeller and the geophysicist understanding to geologic rule; Can realize the expression that is interrupted of bed boundary place speed, supply strong the support for ray tracing has;
3, the present invention utilizes symbolic distance field and stratum binary tree, has formed a whole set of rational ray intersection, reflection and refraction rule, has effectively improved accuracy for ray tracing and efficient.
Description of drawings
Fig. 1 is tectonic structure section and the corresponding stratum binary tree that generates;
Fig. 2 is the tetrahedron synoptic diagram that intersects with stratal surface;
Fig. 3 is that the rate pattern with dual duplicate is expressed synoptic diagram;
Fig. 4 is the complex geological structure model that has a plurality of tomographies;
Fig. 5 is reflection, the refraction synoptic diagram of injection line in the complex structure model;
Fig. 6 is the propagation synoptic diagram that inner point source ray arbitrarily arrives certain section in the complex structure model;
Fig. 7 is the complex geological structure model that has the body of pestering;
Fig. 8 is propagation (only the consider reflection) synoptic diagram of inner point source ray arbitrarily at the complex geological structure model that has the body of pestering;
Fig. 9 has the diagrammatic cross-section of propagating in the tectonic model of high versus speed for ray on mushroom body border;
Figure 10 is the corresponding rate pattern of seismic exploration geological structure model practically;
Propagation (only the considering refraction) synoptic diagram that Figure 11 is inner point source ray arbitrarily in seismic exploration geological structure model practically;
The structure wavefront surface synoptic diagram that Figure 12 propagates in seismic exploration geological structure model practically for inner point source ray arbitrarily.
Embodiment
Below in conjunction with description of drawings embodiment of the present invention.
A kind of interface perception ray-tracing scheme of expressing based on implicit model comprises three steps, comprising:
Steps A, geological interface and geologic body generation method construct three-dimensional geologic structure model based on implicit expression comprise symbolic distance field and stratum binary tree;
Wherein, based on the geological interface and the geologic body generation method of implicit expression, can adopt " a kind of stratal surface and geologic body generation method " (to obtain national patent in the steps A based on level set; License number is ZL200810112263.6); The mathematical method that also can take other for each aspect generate corresponding symbol data field (like Frank, T., Tertois; A.L.; Mallet, J.L., 2007.3D-reconstruction of complex geological interfaces from irregularly distributed and noisy point data.Computer&Geosciences 33:932-943; Calcagno, P., Chiles; J., Courrioux, G.; Guillen, A., 2008; Geological modeling from field data and geological knowledge-part I:Modelling method coupling 3D potential-field interpolation and geological rules:Physics of the Earth and Planetary Interiors 171 (1-4), 147-157.) aspect is as the zero contour surface of symbol data field.
Implied expression method symbolization distance field is expressed implicit surface as representation with the zero contour surface of symbolic distance field.In the present invention, be each stratal surface structure symbolic distance field, the zero contour surface of symbolic distance field is in order to express the geology aspect.Simultaneously; Defined a kind of data structure of describing geology aspect and geologic body spatial topotaxy---stratum binary tree; It has following character: each non-leaf node is represented an aspect, the area of space that each leaf node representative aspect is cut apart, i.e. stratum body; Main stratum is the father or the ancestor node on respective secondary stratum always; To arbitrary stratum binary tree node, its left sibling, oneself, its corresponding aspect of right node that always becomes sequence or reverse sequence arranges.Fig. 1 is the synoptic diagram of tectonic structure section and its corresponding stratum binary tree that generates, wherein, and Si (i=1,2; 3,4) represent stratal surface, corresponding to the upper surface of stratum body; Ti (i=1,2 ...; 9) representative is by the spatial sub of stratigraphic division zone, and stratum S2 is divided into T1 and T2 two subregions with area of space among the figure, and two sub regions are divided respectively again.
Step B, automatic desin speed model on the three-dimensional structure model basis of implied expression;
Step B1; According to stratum binary tree and symbolic distance field is that each stratum body is specified tetrahedral grid; These tetrahedral grids comprise and are positioned at stratum body tetrahedral grid inner and that intersect with stratum body outland aspect fully, crossing tetrahedral grid with its Different Strata body that intersects in respectively preserve a duplicate;
Step B2 is that velocity amplitude is composed on the tetrahedral grid summit of each stratum body appointment according to the speed create-rule, and is unit organization speed file with the stratum body; Speed generates rule and is determined jointly by stratal surface base velocity function and velocity gradient, and wherein velocity gradient derives from sand smeller and geophysicist's priori or obtained by migration velocity analysis.
The speed modeling is a kind of attribute modeling in essence, and is very high to the rate pattern accuracy requirement when rate pattern is applied to the ray tracing of interface perception, and particularly at the interface speed is expressed on tomography, stratum etc.Existing manyly be used for the ray tracing of aspect perception, but these main difficulties based on the interface perception velocities modeling algorithm of grid are the model constrained grid generation down of complex structure based on the speed modeling method of grid.A main challenge based on the speed modeling of implied expression is that the implicit expression stratum is not the tetrahedral grid interface, does not have grid vertex corresponding to stratal surface.Searching the affiliated stratum of each grid vertex and be their assignment, is a kind of consuming time and clumsy way through enumerating or comparing with structure at all levels.How the grid that those and aspect are intersected has different solutions for each summit tax velocity amplitude.Because not all four summits all from same stratum body, are that internal point is composed the result that velocity amplitude can lead to errors through direct approach based on linear interpolation.People such as Bargteil in 2007 have proposed a kind of method during one type of similar problem in rebuilding solving geologic body; The tetrahedron that this method is positioned at above or below the stratum fully is set to constant, for and the tetrahedron that intersects of aspect then adopt the approximate strategy of a kind of body according to the ratio between two kinds of materials.For the solid material of plastic yield, this is a kind of simple but effective method, but and is not suitable for the speed modeling of ray tracing.Because in the ray tracing process, the crossing calculating of a large amount of rays and aspect is arranged, the inaccurate calculating that can influence directions of rays of the speed that aspect is adjacent.
In the isotropic medium, speed can be had constant gradient, exponential function, conical function or analyzable characteristic by definition.Because the deposition characteristics on stratum makes tectonic structure have transversely isotropic symmetrical feature, at vertical depth direction, speed possibly no longer be the constant gradient.Yet at dynamic structure realm, through long-term structural evolution, the stratum maybe run-off the straight, thereby causes the inclination of lateral symmetry axle.Most seismic prospecting research all is based on the layered geology model, because deposition characteristics, speed is linear change in the layer.Yet increase with the vertical degree of depth, always the variation of speed maybe be not continuous, when particularly running into the stratum.Therefore, need a kind of rate pattern of learning understanding of structure, the speed that makes changes in layer continuously, and possibly be interrupted in the aspect junction with meeting.
Based on above geological knowledge, the rate pattern that is used for ray tracing and inverting must be consistent with the distribution of stratum media.Therefore, the speed modeling mainly comprises two parts: be that the stratum body specifies tetrahedral grid, and be that grid vertex is composed velocity amplitude according to inclination transverse isotropy principle.The present invention has adopted a kind of velocity gradient method to calculate the speed of grid vertex in each stratum body.At first; For each stratum body round floor is specified a 2D base velocity function v (x; Y), basic velocity amplitude on the bed interface, base area and velocity gradient (be generally sand smeller and geophysicist's priori or obtain) by migration velocity analysis, use the speed in the body of computes stratum:
v(P)＝v
0(P)+g*h(P)
In the formula, the velocity amplitude of the tetrahedral grid summit P that v (P) indicates to ask for, v
0(P) for specifying the basic velocity amplitude of bed boundary, g is the velocity gradient of stratum body, and h (P) expression summit P is to the normal direction distance on stratum.Obviously, h (P) can be directly calculated by the symbolic distance field of stratigraphic structure model, tracks stratal surface according to symbolic distance field negative gradient direction from P equally, can obtain stratum base speed v
0(P).
Rate pattern is subdivided into tetrahedral grid, in the ray tracing process, need to use ray the velocity amplitude of each grid vertex of process.The velocity amplitude of tetrahedron element internal point is got by the velocity amplitude linear interpolation on four summits, but for the tetrahedral grid that intersects with aspect, this interpolation method is just no longer suitable.Because bed boundary does not have the constraint information that explicitly is defined as tetrahedral grid, and can not be expressed by tetrahedral triangular topological relations with the stratal surface of implicit method expression.Therefore, if only use the simple interpolations method, the velocity amplitude of grid and aspect intersection just possibly incorrectly maybe can't be explained.Shown in Fig. 2 a, intersect on tetrahedral grid unit and stratum, and summit A is positioned on the stratal surface, and other three summit B, C and D are positioned under the stratal surface, will calculate the velocity amplitude of internal point E now.If directly use the velocity amplitude on four summits to carry out linear interpolation, the E spot speed value that obtains so maybe be incorrect or be made us and can't explain, gets because of A point and B, C, D three spot speed values use different speed gradient calculation.The ray tracing of the mistake that the velocity amplitude of mistake will cause, and these bed boundary places are the very responsive zones of ray tracing, very important to ray tracing, it will determine the direction of ray.
The present invention has adopted the method for dual duplicate to solve this problem; Velocity amplitude for the point in the crossing grid cell on the calculating aspect; Stratum body speed create-rule on the aspect is extended to all summits (comprise on the aspect with under) of this crossing grid cell, and the velocity amplitude on these summits is recorded in the aspect overlying strata body speed file.For the summit under the aspect that is positioned at of intersecting grid cell; Make and use the same method; Stratum body speed create-rule under the aspect is extended to all summits of this crossing grid cell, and the velocity amplitude on these summits is recorded in the speed file of aspect sub-surface body.For more complicated stage construction and the crossing situation of grid cell, like Fig. 2 b, this method also is easy to expand to the method for multiple duplicate; For each stratum body generates the speed file that different duplicates are arranged; That is,, then have a plurality of these tetrahedral friction speed value duplicates and exist if tetrahedron and a plurality of stratum body intersect; And be recorded in the speed file of corresponding stratum body, Fig. 3 describes the method for speed assignment.
Therefore, the speed modeling process also needs respective extension.To each stratum body, need search the tetrahedral grid that is positioned at the stratum body and intersects, and use the speed create-rule of this stratum body to be tetrahedral grid summit assignment with its stratal surface.Main difficulty in the realization is how to search these tetrahedrons.Specific practice is: to each stratum body; Travel through all tetrahedral grids; Use symbolic distance field and stratum binary tree; It is interior or crossing with stratal surface to confirm whether tetrahedron is included in the stratum body, and usually, the path of searching in the binary tree of stratum is the path of tracing back to root node from the leaf node of representing this stratum body.For example, it is interior or crossing with it to check whether tetrahedron C is included in stratum body S, and the ergodic process in the binary tree of stratum begins from the leaf node of expression stratum body S, defines the process of its traversal of iterator indication.At first; Iterator points to the father node (nonleaf node is represented the geology aspect in the binary tree of stratum) of this leaf node; If stratum body S is positioned at a side on the indicated stratum of iterator; And all summits of tetrahedron C are positioned at opposite side, can confirm that then this tetrahedron is not included among the body S of stratum or intersect with it, and traversal stops; Otherwise upgrade the position of iterator, review along the ancestors path, until root node, if trace back process is never violated Rule of judgment, can confirm then that tetrahedron S is included among the body S of stratum or with it intersects.When find all be included in stratum body S or with its tetrahedron that intersects after, be this stratum body tax velocity amplitude according to the speed create-rule, and generate its corresponding speed file.
Step C carries out ray tracing according to tectonic model and rate pattern.
Step C1 according to kinematical equation, adopts the method for cutting apart when waiting, and the raypath segmentation is calculated; Each calculates segmentation and is called a ray step, and to each ray step, if itself and the border triangle intersect of tetrahedron element, it will be blocked by this face so, and joining becomes this ray and goes on foot new terminal point.
The kinematical equation of ray tracing belongs to eikonal equation, and Cerveny use characteristic method has been described its concrete form, as shown in the formula:
du＝v
ndτ
Can find out from above-mentioned equation, along ray tracing x
iAnd distribution p
iIt is the function of monotone increasing independent variable u.x
i(u) be called as raypath, use this set of equations can obtain the iterative computation formula of raypath.Ray tracing begins from source point, and analog wave front construction method is launched one group of ray that is constant increment angle APPROXIMATE DISTRIBUTION.No matter when, when the adjacent ray of topology surpassed certain distance apart, a new ray can be inserted into to safeguard wavefront shape.Cut apart segment iteration during raypath employing etc. and calculate, each calculates segmentation and is called a ray step.To each ray step, if its certain face with tetrahedron element intersects, it will be blocked by this face so, and joining becomes this ray and goes on foot new terminal point.Simultaneously, carry out mark, see whether its crossing face is positioned at tomography, because refraction or reflection will take place at the tomography place ray this intersection point.
Step C2, whether the inspection ray step intersects with tomography: express because fault surface adopts the tetrahedral grid face to show, and cancelled tomography both sides tetrahedron topological adjacency relation; The adjacent tetrahedron of sharing fault surface keeps a common sides duplicate separately; When ray step and tetrahedral border triangle intersect, check whether this face is fault surface, if; Then this ray step terminal point is labeled as and is positioned at tomography, promptly this ray step intersects with tomography;
Step C3; Whether the inspection ray step intersects with stratal surface; Because stratal surface has adopted the latent function that shows to express; Can not directly judge crossingly, can use the rule of judging spatial point layer position in the binary tree of stratum, to confirm:, can confirm that this ray step is positioned at certain stratum body fully and does not have with stratal surface crossing if starting point and the terminal point in ray step are positioned at the same leaf node of stratum binary tree; Otherwise this ray step intersects with a stratal surface at least.Further confirm the definite position of intersection point: each node on checking from this stratum, ray step starting point place body leaf node to the ancestral path of tracing back of root node; For nonleaf node; If starting point and terminal point opposite in sign in the symbolic distance field in ray step; Can confirm that then ray step and this stratal surface intersect, the starting point in ray step and the ratio of the value of terminal point in the symbolic distance field can be confirmed the definite position of intersection point.
Because stratal surface does not have explicitly and is expressed as grid surface, therefore need the further inspection ray step whether to intersect with a certain stratal surface, judge that the rule of spatial point layer position can help realization.If the starting point and the terminal point in ray step are positioned at the same leaf node of stratum binary tree, can confirm that this ray step is positioned at certain stratum body fully and does not have with stratal surface crossing; Otherwise this ray step intersects with a stratal surface at least.In order to confirm the definite position of intersection point, at first need find out this ray step terminal point position.Therefore, in the binary tree of stratum, all possibly become checked object to each node on the ancestral path of tracing back of root node from this stratum, ray step starting point place body leaf node.For each nonleaf node (stratal surface); If starting point and terminal point opposite in sign in the symbolic distance field in ray step; Can confirm that then ray step and this stratal surface intersect; Simultaneously because the symbolic method that the starting point in ray step and the value representation of terminal point in the symbolic distance field are put aspect to distance, therefore can be confirmed the definite position of intersection point by the ratio of distance value.In case after confirming intersection point, the ray step will be blocked, intersection point will become new terminal point of ray step.
Reflection and refraction when the ray step intersects with tomography or stratum, will take place in step C4, use the symbolic distance field, can calculate the normal vector at ray and aspect joining place rapidly, with convenient ray incident angle and the emergence angle calculated.When the ray step intersected at tomography, the reflected ray step still carried out in the current tetrahedron of current stratum body, but has new directions of rays; Refracted rays step will carry out sharing in the adjacent tetrahedron of fault surface with current tetrahedron; Can confirm stratum, new tetrahedron place body according to the rule of judging spatial point layer position; If body not on current stratum; Need to load corresponding stratum body speed file, and use the speed create-rule of new stratum body to go on foot point interpolation to go out velocity amplitude as refracted rays.When the ray step intersected at the stratum, the reflected ray step still carried out in the body of current stratum, but has new directions of rays; The refracted rays step will originate in new stratum body, and new stratum body uses the rule of the judgement spatial point layer position of revising to confirm, and loads corresponding stratum body speed file, uses new tetrahedron duplicate to go on foot point interpolation as refracted rays and goes out velocity amplitude.
The rule of the judgement spatial point layer position among step C3 and the C4 is meant: the binary tree root node begins the selectivity traversal from the stratum; Go out the value of given spatial point by interpolation in the symbolic distance field of the corresponding aspect of current binary tree node; The next child node that travels through of symbol decision by this value is left child node or right child node; So continue traversal, promptly provided layer position, spatial point place until arriving at leaf node; Being meant of the rule of the judgement spatial point layer position of revising: when the nonleaf node of traversal to crossing stratum, if current stratum body is positioned at left subtree, then continue traversal from right subtree, vice versa.
If effective terminal point in ray step is positioned at stratal surface, reflection and refraction will take place in ray.The reflected ray step still originates in current stratum body but has had different directions, and the refracted rays step will originate in new stratum body, and starting point was the terminal point in last ray step, and the speed file that needs to load new stratum body calculates.So, how to find the new stratum body at refracted rays step place? Directly use the rule of judging spatial point layer position can run into some molehills, because starting point is located immediately on the stratal surface.For this reason, the rule of judging spatial point layer position is carried out simple modifications: when the nonleaf node of traversal to crossing stratum, if current stratum body is positioned at left subtree, then continue traversal from right subtree, vice versa.
Use the rule of revised judgement spatial point layer position, can confirm the stratum body at refracted rays step place rapidly, and load corresponding speed file and calculate.Have dual duplicate owing to intersect tetrahedron element with aspect, the velocity amplitude of the ground zero in refracted rays step will carry out interpolation according to the tetrahedron duplicate in the body speed file of new stratum.
If the ray step does not intersect with any stratum, need inspection ray step terminal point whether to be marked as and be positioned at tomography, if be positioned at tomography, reflection and refraction also will take place in the ray step so.As previously mentioned; Because cancelled tomography both sides tetrahedron topological adjacency relation, the tetrahedron that tomography is shared face keeps a duplicate separately, so the reflected ray step still carries out in the current tetrahedron of current stratum body; Only had new directions of rays; And refracted rays step will carry out in the tetrahedron of fault surface sharing with current tetrahedron, can confirm stratum, new tetrahedron place body according to the rule of judging spatial point layer position, if the body on current stratum not; Then need load corresponding stratum body speed file, and use new tetrahedron duplicate to go on foot point interpolation to go out velocity amplitude as refracted rays.
Reflection and refraction can take place when ray runs into the interface, and the Snell law has been described this rule.According to the Snell law, the present invention uses the parameter of computes ray at p point place:
V in the formula (r) ray is velocity of propagation at degree of depth r place, i be ray at the degree of depth r place incident angle.
Tradition ray-tracing scheme unusual difficulty often when calculating the exit direction of ray at a certain intersection point place is particularly at the subterranean zone of complex structure.Among the present invention; Owing to adopt implicit method to express stratal surface, introduced symbolic distance field and stratum binary tree, can make things convenient for and easily calculate the normal vector at ray and aspect joining place; Thereby calculate the ray exit direction in step fast, this is particularly favourable for extensive crossing calculating.And; When ray and aspect each time intersect computing; Can both obtain the parameters such as interfacial curvature matrix such as joining locus, interfacial vector and corresponding topical coordinate, these all are for ray reflection and refraction and kinematics and the important and sufficient information of kinetic parameter calculating ten minutes.
In sum, provide following embodiment.Fig. 4～shown in Figure 12 is the ray tracing synoptic diagram of the embodiment of the invention.Fig. 4～Fig. 6 follows the trail of synoptic diagram for ray at the complex geological structure model with multi-fault, and wherein, Fig. 4 is the 3 D complex geological structure model of input; Fig. 5 has shown the concrete situation that the wall scroll ray is propagated in this model, comprise reflection situation and refraction situation; Fig. 6 is the propagation synoptic diagram that the fan-shaped divergent-ray arrives a certain section for the inner any point source of this model.Fig. 7～Fig. 9 follows the trail of synoptic diagram for ray at the complex geological structure model with mushroom body, and wherein, Fig. 7 is the 3 D complex geological structure model that has the body of pestering; Fig. 8 is the propagation synoptic diagram that the inner any point source of model is the fan-shaped divergent-ray, the situation of the ray reflection that this synoptic diagram is only considered; Fig. 9 has the diagrammatic cross-section of propagating under the situation of high versus speed for ray on mushroom body border.Figure 10～Figure 12 is the synoptic diagram of embodiment of the present invention instance ray-tracing scheme in the complex geological structure model in the seismic exploration practically; Wherein, Figure 10 is the corresponding rate pattern of complex geological structure model that uses the implied expression method construct practically in the seismic exploration; Figure 11 is the propagation synoptic diagram that the inner point source arbitrarily of model is the fan-shaped divergent-ray, the situation of the broken line reflection that this synoptic diagram is only considered; Figure 12 is the structure wavefront surface synoptic diagram in this actual geologic model.
Certainly; The present invention can also have other various embodiments; Under the situation that does not deviate from spirit of the present invention and essence thereof; Those of ordinary skill in the art work as can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection domain of the appended claim of the present invention.
Claims (6)
1. an interface perception ray-tracing scheme of expressing based on implicit model is model constrained down at the three-dimensional geologic structure of implicit method expression, and automatic desin speed model carries out ray tracing, is used for the system of seismic exploration data inverting, modeling and skew; It is characterized in that, may further comprise the steps:
Steps A, geological interface and geologic body generation method construct three-dimensional geologic structure model based on implicit expression comprise symbolic distance field and stratum binary tree;
Step B, automatic desin speed model on the three-dimensional structure model basis of implied expression;
Step C carries out ray tracing according to tectonic model and rate pattern.
2. a kind of interface perception ray-tracing scheme of expressing based on implicit model according to claim 1; It is characterized in that; Symbolic distance field in the said steps A is the implied expression form of tectonic model, and the zero contour surface of symbolic distance field is in order to expression corresponding geological aspect.
3. a kind of interface perception ray-tracing scheme of expressing based on implicit model according to claim 1; It is characterized in that; Stratum binary tree in the said steps A is a data structure of describing geology aspect and geologic body spatial topotaxy; Have following character: each non-leaf node is represented an aspect, the area of space that each leaf node representative aspect is cut apart, i.e. stratum body; Main stratum is the father or the ancestor node on respective secondary stratum always; To arbitrary stratum binary tree node, its left sibling, oneself, its corresponding aspect of right node that always becomes sequence or reverse sequence arranges.
4. a kind of interface perception ray-tracing scheme of expressing based on implicit model according to claim 1 is characterized in that said step B further comprises:
Step B1; According to stratum binary tree and symbolic distance field is that each stratum body is specified tetrahedral grid; These tetrahedral grids comprise and are positioned at stratum body tetrahedral grid inner and that intersect with stratum body outland aspect fully, crossing tetrahedral grid with its Different Strata body that intersects in respectively preserve a duplicate;
Step B2 is that velocity amplitude is composed on the tetrahedral grid summit of each stratum body appointment according to the speed create-rule, and is unit organization speed file with the stratum body; Speed generates rule and is determined jointly by stratal surface base velocity function and velocity gradient, and wherein velocity gradient derives from sand smeller and geophysicist's priori or obtained by migration velocity analysis.
5. a kind of interface perception ray-tracing scheme of expressing based on implicit model according to claim 1 is characterized in that said step C further comprises:
Step C1 according to kinematical equation, adopts the method for cutting apart when waiting, and the raypath segmentation is calculated; Each calculates segmentation and is called a ray step, and to each ray step, if itself and the border triangle intersect of tetrahedron element, it will be blocked by this face so, and joining becomes this ray and goes on foot new terminal point;
Step C2, whether the inspection ray step intersects with tomography: express because fault surface adopts the tetrahedral grid face to show, and cancelled tomography both sides tetrahedron topological adjacency relation; The adjacent tetrahedron of sharing fault surface keeps a common sides duplicate separately; When ray step and tetrahedral border triangle intersect, check whether this face is fault surface, if; Then this ray step terminal point is labeled as and is positioned at tomography, promptly this ray step intersects with tomography;
Step C3; Whether the inspection ray step intersects with stratal surface; Because stratal surface has adopted the latent function that shows to express; Can not directly judge crossingly, can use the rule of judging spatial point layer position in the binary tree of stratum, to confirm:, can confirm that this ray step is positioned at certain stratum body fully and does not have with stratal surface crossing if starting point and the terminal point in ray step are positioned at the same leaf node of stratum binary tree; Otherwise this ray step intersects with a stratal surface at least; Further confirm the definite position of intersection point: each node on checking from this stratum, ray step starting point place body leaf node to the ancestral path of tracing back of root node; For nonleaf node; If starting point and terminal point opposite in sign in the symbolic distance field in ray step; Can confirm that then ray step and this stratal surface intersect, the starting point in ray step and the ratio of the value of terminal point in the symbolic distance field can be confirmed the definite position of intersection point;
Reflection and refraction when the ray step intersects with tomography or stratum, will take place in step C4, use the symbolic distance field, can calculate the normal vector at ray and aspect joining place rapidly, with convenient ray incident angle and the emergence angle calculated; When the ray step intersected at tomography, the reflected ray step still carried out in the current tetrahedron of current stratum body, but has new directions of rays; Refracted rays step will carry out sharing in the adjacent tetrahedron of fault surface with current tetrahedron; Can confirm stratum, new tetrahedron place body according to the rule of judging spatial point layer position; If body not on current stratum; Need to load corresponding stratum body speed file, and use the speed create-rule of new stratum body to go on foot point interpolation to go out velocity amplitude as refracted rays; When the ray step intersected at the stratum, the reflected ray step still carried out in the body of current stratum, but has new directions of rays; The refracted rays step will originate in new stratum body, and new stratum body uses the rule of the judgement spatial point layer position of revising to confirm, and loads corresponding stratum body speed file, uses new tetrahedron duplicate to go on foot point interpolation as refracted rays and goes out velocity amplitude.
6. a kind of interface perception ray-tracing scheme of expressing based on implicit model according to claim 5 is characterized in that, in the rule of the rule of the judgement spatial point layer position among described step C3 and the C4 and the judgement spatial point layer position of correction:
The rule of judging spatial point layer position is meant: the binary tree root node begins the selectivity traversal from the stratum; Go out the value of given spatial point by interpolation in the symbolic distance field of the corresponding aspect of current binary tree node; The next child node that travels through of symbol decision by this value is left child node or right child node; So continue traversal, promptly provided layer position, spatial point place until arriving at leaf node;
Being meant of the rule of the judgement spatial point layer position of revising: when the nonleaf node of traversal to crossing stratum, if current stratum body is positioned at left subtree, then continue traversal from right subtree, vice versa.
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