CN102053263A - Method for inspecting surface structure - Google Patents

Abstract

The invention provides a method for inspecting a surface structure, which comprises the steps of: a, extracting first-motion wave real arrival time from seismic wave data acquired by a plurality of seismic channels along seismic survey lines and forming a real arrival time matrix; b, obtaining a velocity matrix or slowness matrix used for reflecting the surface structure according to the real arrival time matrix based on a chromatography inversion method; and c, establishing a model used for reflecting the relationship of the velocity and the depth of the surface structure or a model used for reflecting the relationship of the slowness and the depth of the surface structure based on the velocity matrix or slowness matrix used for reflecting the surface structure and obtained from the step b. The method for obtaining the near surface structure, provided by the invention, has low cost, high speed and wide application range and is very effective.

Description

The method of investigation surface structure

Technical field

The present invention relates to the geophysical survey field, more particularly relate to a kind of method of investigating surface structure.

Background technology

Seismic prospecting is to produce seismic event by the artificial excitation, explores underground geological condition by research seismic event propagation law in the different stratum of elasticity.The main process of seismic prospecting can be divided into three phases: seismic data acquisition, seismic data are handled and seismic data interpretation, finally obtain the geology result.

Seismic data acquisition is to produce seismic event by artificial method, for example use explosive as focus, fired charge produces seismic event, writes down by the caused earth shock signal of the underground seismic event that reflects with earthquake receiving instrument device then, obtains the corresponding geological sectional view by computing.

In the seismic data acquisition process, near near surface, in the certain depth scope, have the very low stratal configuration of a kind of speed, seismic event by the time can spend more time, the stratum of this depth range is called weathering zone.In certain areas, between weathering zone and high-velocity zone, also there is a zone of transition that speed is on the low side, be called the reduction of speed band.The speed and the thickness of weathering zone, reduction of speed band alter a great deal on vertical and horizontal, elapsed time was also different when therefore seismic event was through the different layers band, this temporal difference handles for follow-up seismic data bring very big trouble, as can not be with superimposed, and underground imaging difficulty etc.Therefore, the seismic section of underground truth be obtained to reflect, just the influence of surface structure must be eliminated seismic event.

In order to eliminate the influence of surface structure to seismic event, just must grasp some physical parameters on top layer, comprise relevant data situations of change spatially such as speed, the degree of depth, lithology, this is called the surface structure investigation in geological exploration techniques.For surface structure investigation, development in recent years goes out a lot of methods, and commonly used have little refraction, a micro logging etc.Chapter 3 the 7th joint describes key concept and several common method of surface structure investigation in detail in " the prospecting seismology study course " that Zhu Guangsheng, Chen Chuanren, the osmanthus will that publishing house of Wuhan University publishes is write earlier (2005 Dec the 1st edition) book.The publication number of Sun Suomei is that CN101178439, denomination of invention are also to have introduced the problem of little refraction, micro logging method and existence thereof in the surface structure investigation in " accurately surface investigation method ", has proposed a kind of construction method that the micro logging method is used to improve existing micro logging that reflects.Below above document, simply introduce little refraction method commonly used in the prior art and micro logging method and limitation separately.

Little refraction method is to utilize low velocity layer (LVL) and high-velocity bed interphase easily to produce refraction wave and the easy characteristics of refraction wave exploration.The first break refraction method utilizes the T-X curve of first arrival direct wave and shallow refraction ripple to find the solution the thickness and the speed of weathering zone.The execution conditions of little refraction generally are that the surface structure that is used to follow the trail of is more shallow, and the little mild area of surface relief, otherwise can bring bigger error even mistake to explanation results.

Micro logging is a kind of method of directly measuring weathering zone, reduction of speed band parameter in well.This method at first will have a bite drilling well, wave detector is placed in the well, excite on the face of land near well head, whenever excite a wave detector to move a position from deep to shallow, the each direct wave that receives of seismograph record, read the first break time and the observation speed of direct wave,, make the vertical T-X curve of time-degree of depth through data compilation.The micro logging method is than little refraction process precision height, but cost is higher than little refraction process, and speed is also slow.

Summary of the invention

The little refraction method that the present invention is directed in the surface structure investigation method of prior art is only applicable to the little area of surface relief and the high restriction of micro logging method cost, the method of the investigation surface structure that a kind of cost is low, speed is fast, applied widely has been proposed thus.

The invention provides a kind of method of investigating surface structure, this method comprises:

(a) from the seismic data of gathering, extract the primary wave real travel time, and form the real travel time matrix along a plurality of seismic traces of seismic line;

(b) obtain being used to reflect the speed matrix or the slowness matrix of surface structure based on chromatography conversion method according to described primary wave real travel time matrix;

(c) reflect that based on step (b) being used to of obtaining the speed matrix of surface structure or slowness matrix set up slowness and the depth relationship model that is used to reflect the speed and the depth relationship model of surface structure or is used to reflect surface structure.

The method of investigation surface structure of the present invention, medium velocity model behind the employing tomographic inversion is explained surface structure, reached achievement with micro logging method precision of the prior art equivalence, and this method can be broken away from the restriction of the medium and small refraction method of prior art execution conditions and the restriction of micro logging cost, go for the big higher zone of drilling cost of bigger landform of topographic relief and surface structure thickness, the little refraction method of the interpretation results ratio of precision height of method provided by the invention, and the near surface structure quantity of information is than little refraction, micro logging is abundanter, construction method is simple, convenient, be a kind of more efficiently surface structure investigation method.

Description of drawings

Fig. 1 is the process flow diagram according to the method for investigation surface structure of the present invention;

Fig. 2 is that the chromatography conversion method that utilizes among Fig. 1 obtains the particular flow sheet of speed matrix step;

Fig. 3 is a synoptic diagram of setting up initial velocity model;

Fig. 4 is the synoptic diagram of shortest path ray-tracing scheme;

Fig. 5 is the model synoptic diagram of given theoretical seismic section to be measured;

Fig. 6 utilizes the method for investigation surface structure of the present invention the seismic section model of Fig. 5 to be analyzed the speed-depth relationship synoptic diagram that obtains;

Fig. 7 is and Fig. 6 time corresponding-depth relationship synoptic diagram.

Embodiment

As depicted in figs. 1 and 2, the invention provides a kind of method of investigating surface structure, this method comprises:

(a) from the seismic data of gathering, extract the primary wave real travel time, and form the real travel time matrix along a plurality of seismic traces of seismic line;

(b) obtain being used to reflect the speed matrix or the slowness matrix of surface structure based on chromatography conversion method according to described primary wave real travel time matrix;

(c) reflect that based on step (b) being used to of obtaining the speed matrix of surface structure or slowness matrix set up slowness and the depth relationship model that is used to reflect the speed and the depth relationship model of surface structure or is used to reflect surface structure.

Wherein step (b) may further comprise the steps:

(b1) for given initial velocity matrix or initial slowness matrix, theory of computation whilst on tour matrix t and theoretical raypath matrix M;

(b2) theoretical whilst on tour matrix that step (b1) is tried to achieve and theoretical raypath matrix substitution inversion equation Ms=t, obtain new speed matrix or slowness matrix to upgrade initial velocity matrix or initial slowness matrix, wherein M is the raypath matrix, t is the whilst on tour matrix, s is the slowness matrix, v is the speed matrix, s=1/v; With

(b3) based on new speed matrix or the slowness matrix obtained in the step (b2), till the root mean square average of the difference between repeating step (b1) and step (b2) each corresponding whilst on tour in theoretical whilst on tour matrix and real travel time matrix was no more than predetermined threshold, speed matrix or the slowness matrix that try to achieve this moment were the speed matrix or the slowness matrix that are used to reflect surface structure that utilizes chromatography conversion method to ask for.

Employing well known to a person skilled in the art the seismic event mode of excitation, and for example explosive source excites, detonator excites, knock and excite etc., and carries out the reception of seismic data in conjunction with seismoreceiver etc., can obtain seismic data.It is the element task of seismic prospecting that seismic event excites, and describes the selection of various focus and shooting conditions in " seismic prospecting study course " chapter 3 the 4th joint that Zhu Guangsheng etc. write in detail.Usually, can arrange a plurality of shot points on seismic line, the surface structure degree of depth that the arrangement pitches of shot point can be investigated as required determines that the maximum offset of arranging should be not less than the twice of the depth capacity of detection usually.After the epicenter excitation, pass through under the seismic event that produces boundary reflection, the up face of land that turns back to, refraction back, can receive and note by seismoreceiver, describe the selection of spread length in the reception of seismic event, the problems such as arrangement of seismoreceiver in " seismic prospecting study course " chapter 3 the 5th joint that Zhu Guangsheng etc. write in detail by seismograph.Usually can be on seismic line distribution seismic trace arbitrarily, if shake evenly distributedly, be the surface structure of accurate description more, the track pitch of seismic trace preferably is chosen between the 1m to 10m.

The purpose of picking up primary wave from seismic data is will obtain seismic event by the minimum ray propagates time of shot point to acceptance point, i.e. primary wave real travel time is with the objective function when ray is walked in the chromatography conversion method.Pick up on common-shot-gather and carry out, the scope of the primary wave that picks up will be decided according to the maximal rate of low reduction of speed layer in the geologic province of inverting and the degree of depth.Because tomographic inversion need utilize the constraint of earthquake first arrival whilst on tour to come the inverting near-surface velocity model, accuracy requirement to the earthquake travel-times of seismic first breaks extracted is higher, thereby, preferably, after receiving the seismic event that excites, pick up all primary waves, and reject the primary wave (seismic record too low) of partial invalidity as signal to noise ratio (S/N ratio).In order to raise the efficiency and to be convenient to discern seismic event, all on many observation stations, receive simultaneously during each artificial excitation's seismic event, so seismograph generally is a multiple tracks.The quantity of element can equal the quantity in regional earthquake to be measured road in the real travel time matrix that the primary wave real travel time that extracts from seismic data is constructed.Suppose to have N seismic trace, then from seismic data, extract the real travel time matrix of being constructed behind the real travel time and can form by N whilst on tour.

The surface-level model chromatography conversion method is a kind of nonlinear model inversion technique, and inverting medium velocity structure is come in when it utilizes walking of earthquake primary wave ray and path, is not subjected to the face of land and near surface structure in length and breadth to the constraint that changes.According to the error of just drilling whilst on tour and real travel time, the erection rate model through iterating, finally meets the requirements of error precision.Xun's chapters etc. are in " tell and breathe out oil gas " the 10th the 4th phase of volume, in October, 2005, the name of delivering is called the paper of " the rate pattern tomographic inversion static correction of primary wave top layer ", Wenjun YANGs etc. are in " physical prospecting and geochemical exploration " the 29th the 1st phase of volume, in February, 2005, the name of delivering is called " tomographic inversion static correction " paper, Luo Shengxian etc. are at " Advances in Earth Science " the 19th volume supplementary issue, in June, 2004, the name of delivering is called " the complicated shallow velocity structure method of surface seismic primary wave tomographic inversion ", the name of the Jiang Guobo of China University of Geosciences is called in the Master's thesis of " primary wave surface-level model chromatography FORWARD AND INVERSE PROBLEMS and chromatography static correction research " etc. and all describes chromatography conversion method in detail, all be that chromatography conversion method is used for static correction research in present as can be seen these papers, and chromatography conversion method be not used for the surface structure investigation.

Obtaining based on chromatography conversion method in the process of shallow velocity structure, at first want in the geologic province of inverting, to set up initial velocity model earlier, and to its gridding, promptly carry out the binning of rate pattern grid, its objective is to tomographic inversion provides an initial velocity amplitude and spatial dimension, make the inverting iterative process in limited speed and space, carry out.The speed and the precision of the size decision inverting of grid bin.The lateral separation of grid bin (being horizontal sampling interval) is generally chosen and is less than or equal to two adjacent seismological observation points apart from (track pitch), fore-and-aft distance (being vertical sampling interval) will be decided on the degree of depth and cross direction profiles low in the tomographic inversion zone, the reduction of speed band, can be chosen as consistent with lateral separation.As shown in Figure 3, given initial velocity matrix or initial slowness matrix are set up by pressing mode: with the seismic line direction is directions X, with with seismic line direction direction vertically downward be that the Z direction is set up the XZ plane, the directions X length that selection comprises seismic section to be measured is that L, Z direction length are the rectangular area of D, with the straight line of m bar this rectangular area is divided into (n-1) * (m-1) individual rectangular element along the straight line of directions X and n bar along the Z direction, with rectangular element by from left to right, from top to bottom serial number, the speed of establishing in each rectangular element is v _jOr slowness is s _j, j=1 wherein, 2 ..., (n-1) * (m-1), then by (n-1) * (m-1) individual speed v _jOr slowness s _jThe matrix of forming is initial velocity matrix or initial slowness matrix.In setting up initial velocity matrix or initial slowness matrix process, preferably, n and m choose so that the length x of the directions X of each rectangular element _StepLength z with the Z direction of each rectangular element _StepHalf that all is less than or equal to the seismic trace spacing is as the criterion.Like this, line following unit speed (or slowness) in the face of land is the unknown quantity of inverting, and they have constituted solution space.

Finish on the basis of first break picking and setting up on the initial velocity model, can utilize ray tracing just drilling theory of computation whilst on tour matrix and theoretical raypath matrix subsequently.The name of the Jiang Guobo of China University of Geosciences is called in Master's thesis the 2nd chapter of " primary wave surface-level model chromatography FORWARD AND INVERSE PROBLEMS and chromatography static correction research " and describes ray tracing theory and method in detail.The ray-tracing scheme of seismic event is one of effective means of seismic wave propagation problem under the research medium arbitrary speed distribution situation.Can simulate raypath with several different methods, for example fire method, shortest path ray-tracing scheme, linear whilst on tour interpolation method etc. for adjustment.Can utilize the shortest path ray-tracing scheme to come theory of computation whilst on tour and theoretical raypath here.By Fermat principle as can be known, seismic propagation path is followed least time principle, therefore the ray from shot point to the shortest ripple of acceptance point travel-time is the primary wave ray, and be the theoretical whilst on tour of primary wave the time of arrival of this ripple, and the path of this ripple process is the theoretical raypath of primary wave.For the initial velocity model of setting up among Fig. 3, the node of whilst on tour before seismic event when some collections are set on the rectangular element border, as shown in Figure 4, each node in the grid can only be connected with node adjacent one another are.Connection weight between the adjacent node equals the whilst on tour that seismic event is propagated along its line.One paths is made up of interconnective sequence node, is all connection weight sums on this path along the whilst on tour in this path.Have countless paths (as dotted line Fig. 4 and dot-and-dash line) from a node to another, shortest path is exactly the path (as the solid line among Fig. 4) with whilst on tour minimum.According to Fermat (Fermat) principle, just can be approximated to the seismic ray path to shortest path.

just drill try to achieve theoretical whilst on tour matrix and theoretical raypath matrix after, can come the inversion speed matrix based on theoretical whilst on tour of being tried to achieve and theoretical raypath, till the difference between theoretical whilst on tour matrix and real travel time matrix of iterating satisfies certain condition, as till the root mean square average of the difference of each the corresponding whilst on tour between theoretical whilst on tour matrix and the real travel time matrix is less than predetermined threshold, this predetermined threshold can be selected the numerical value less than 10ms, finally obtains reflecting the rate pattern of surface structure.

According to theory of seismic ray, first arrival whilst on tour t and near-surface velocity v have following relationship:

$t=\underset{R\left(v\right)}{\∫}\frac{1}{v(x,z)}\mathrm{dl}$

In the formula: (v) be raypath, it is speed v (x, function z) to R; Dl be along raypath R (distance increment v), x are along the parameter on the seismic line directions X, z be along with seismic line direction Z direction vertically downward on parameter.

If the note s be slowness, promptly s (x, z)=1/v (x, z), then following formula can be expressed as:

$t=\underset{R\left(v\right)}{\∫}s(x,z)\mathrm{dl}$

Following formula is carried out discretize, establish: the slowness of j unit is s _jThe whilst on tour of i bar ray is t _iI bar ray is l by the ray length of j unit _IjLike this, following formula can be separated into:

$\underset{j=1}{\overset{N}{\mathrm{\Σ}}}{l}_{\mathrm{ij}}{s}_j=\underset{i=1}{\overset{M}{\mathrm{\Σ}}}{t}_i,(i=\mathrm{1,2},\·\·\·,M;j=\mathrm{1,2},\·\·\·,N)$

In the formula: M is the whilst on tour number (or penetrating number of lines) of observation; N is the unit number in the rate pattern, for example, M can be the number of the element in the real travel time matrix that extracts from seismic data, also can equal the quantity of seismic trace on the seismic line, for initial velocity matrix of setting up among Fig. 3 or initial slowness matrix, unit number N equals the number (n-1) * (m-1) of rectangular element among Fig. 3.

The relation equation of whilst on tour after the discretize and speed is represented that with matrix (or vector) can be written as Ms=t, M is the raypath matrix in the formula, and t is the whilst on tour matrix, and s is the slowness matrix, perhaps can be written as M/v=t, and v is the speed matrix, v=1/s, wherein:

$s=\left(\begin{array}{c}{s}_1\\ {\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H2009102366223E0000022.png"\; state="\{\{state\}\}">s</figure-callout>}}_2\\ .\\ .\\ .\\ s_N\end{array}\right),$ $t=\left(\begin{array}{c}{t}_1\\ {\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="H2009102366223E0000022.png"\; state="\{\{state\}\}">t</figure-callout>}}_2\\ .\\ .\\ .\\ t_M\end{array}\right),$ $M=\left(\begin{array}{cccc}{l}_{11}& l_{12}& ...& l_{1N}\\ l_{21}& l_{22}& ...& l_{2N}\\ .& .& & .\\ .& .& & .\\ .& .& & .\\ l_{M1}& {\mathrm{<figure-callout\; id="2"\; label="l\; M"\; filenames="H2009102366223E0000022.png"\; state="\{\{state\}\}">l</figure-callout>}}_M& ...& l_{\mathrm{MN}}\end{array}\right)$

Equation Ms=t or M/v=t are and are used for tomographic inversion and ask for the inversion equation that is used to reflect surface structure, in inversion equation, slowness matrix s and raypath matrix M are all unknown, and raypath is again the nonlinear function of slowness, thereby in fact this formula is still the nonlinear equation of slowness.Separate this inverse problem and must adopt successive iteration method.Utilize the previous initial velocity matrix s0 that sets up to carry out iterative computation.Adopt ray tracing just drilling theory of computation raypath matrix and theoretical whilst on tour matrix with the initial velocity matrix, and obtain slowness disturbance quantity δ s, revise initial velocity matrix s=s0+ δ s, obtain new slowness matrix s according to inversion equation Ms=t.Carry out so repeatedly, till the difference of each the corresponding whilst on tour in the first arrival whilst on tour matrix of the theoretical whilst on tour matrix that calculates and observation meets some requirements, root mean square average as the difference of each corresponding whilst on tour (can be the numerical value less than 10ms as this predetermined threshold less than a predetermined threshold, in practice of construction, can select described predetermined threshold according to actual needs, predetermined threshold in the practice of construction also can be a bit larger tham 10ms) till, the pairing speed matrix of slowness matrix that try to achieve this moment is the speed matrix that chromatography conversion method finally obtains.This speed matrix can represent that this speed matrix of describing with the X-Z plane is the near-surface velocity model of seismic region to be studied at X (length)-Z (deeply) in the plane.

Whole velocity profile model can be utilized, certain or some velocity layering positions can be in the velocity profile data of top layer, extracted as required, also can be in the speed-degree of depth sequence of Z (deeply) direction that goes up a certain position of selective extraction correspondence along X (length) to being worth.It should be noted that, in this related degree of depth can be the degree of depth of starting at zero point from the Z axle on X-Z plane, it also can be height value, but also can be the conversion after the layer thickness value, these parameters are all represented to measure longitudinally, and the simple conversion relation between them as those skilled in the known.Specifically, for example,, be used to reflect that the speed of surface structure and depth relationship model can be (v for using the initial velocity matrix set up among Fig. 3 or initial slowness matrix to carry out the speed matrix that obtains behind the tomographic inversion _k, z _k) sequence is right, is used to reflect that the slowness of surface structure and depth relationship model can be (s _k, z _k) sequence is right, k=1 wherein, 2 ..., (n-1) * (m-1), z _kFor with speed v _kThe corresponding degree of depth, z _k=z _Min+ (INT[k/n-1]+1) * z _Step, wherein, z _MinBe the minimum depth value along the straight line of directions X, INT is downward bracket function.

Further describe speed and depth relationship model how to set up the directions X centre section for another example, i grid node list of values of directions X is shown (is that X-axis increases progressively direction from 1 to n) after the survey region model discretize:

x _i＝x _min+(i-1)*x _step (i＝1，2，...，n+1)

X in the formula _MinRepresent the initial value of directions X, x _StepThe mesh spacing value of representing directions X to cut apart.

The m+1 of Z direction node list of values is shown (increasing progressively direction from 1 to m for the Z axle):

z _i＝z _min+(j-1)*z _step (j＝1，2，...，m+1)

Z in the formula _MinRepresent the initial value of directions X, z _StepThe mesh spacing value of representing the Z direction to cut apart.

Then extract directions X center x _cCan be expressed as:

Calculate for simplifying, can directly utilize n/2 on the directions X (n is an even number) or (n+1)/2 the limit of (n is an odd number) individual grid be x _cThe position.The model directions X center x that supposes _cThe high-rise journey in the face of land be h0, and model Z direction minimum value z _MinCorresponding height value is h _Min, ask for the index sequence number that Z direction node in top layer altitude traverse and the grid intersects earlier, suppose here r and r+1 between some, r=1 wherein, 2 ..., m+1.R be by

(INT is downward bracket function) of asking for.

Like this, be that the depth value sequence of reference point correspondence can be expressed as in the Z direction with face of land elevation:

h _k＝h _r，r+1+(k-r)*z _step(k＝r，r+1，...，m+1)

Wherein, h _{R, r+1}Represent the distance value of the intersection point distance r+1 node of the r node of face of land altitude traverse Z direction in the discretize grid model and r+1 node.Can ask for by following formula:

h _r，r+1＝(r+1)*z _step-(h ₀-h _min)

Depth value h _kCorresponding grid node velocity amplitude is:

Wherein: n _c=n/2 (when n is even number) or n _c=(n+1)/2 (when n is odd number), k=r, r+1, r+2 ..., m.

Thus, speed-depth data is to using (v _k, h _k) expression.When enumerating speed-degree of depth sequential value, need (v _r, h _r) as the starting point of sequence.Utilize the method for the investigation surface structure that seismic section modelling verification the present invention theoretical to be measured shown in Figure 5 proposes, each of model layer physical parameter as shown in Figure 5, the position of black vertical curve is exactly the center of model.Here our spread length of selection is 120m, and track pitch is 5m, has excited 5 big guns within the spread length scope.Carrying out grid dividing when setting up initial velocity model, the rectangular area of selected directions X length L=120m, Z direction depth D=50m.Select the x of directions X _StepValue is 2m, the z of Z direction _StepValue is divided into 3000 rectangular elements (m=51 for 1m with selected rectangular area, n=61), the initial velocity value of each rectangular element can be made as use and ask for acquisition along the depth z of Z direction and the linear function v=340+200*z of speed v, wherein the unit of z is a rice, and the unit of speed is a meter per second.Initial velocity model is through tomographic inversion iteration 6 times, and the root-mean-square error of real travel time that has guaranteed each seismic trace is just being drilled after the iteration theoretical whilst on tour and Inversion Calculation thinks that promptly the tomographic inversion result reaches our accuracy requirement within 9.1ms.Fig. 6 is the speed-depth curve figure of model directions X center after the tomographic inversion that extracts.Equally, can also draw time-degree of depth (i.e. (t of directions X center as shown in Figure 7 _k, h _k)) curve map, wherein ask for certain trellis depth h _kTime corresponding value t _kCan use following formula to calculate:

Obtain as shown in Figure 6 and Figure 7 speed-degree of depth or time-depth relationship figure after, the explanation that can adopt conventional near surface investigation method similarly to utilize manual mode of dividing surface structure to carry out near surface structure velocity layering position is extracted and is handled, and finally can reach the achievement with the equivalence of conventional microseismogram log interpretation results.Table 1 is the present invention of obtaining of the result after the theoretical model tomographic inversion at Fig. 5 and the result of conventional interpretation procedure contrasts, the whilst on tour of the arrangement center position 28.4m degree of depth that the rate pattern of inverting of the present invention is asked for is 31.1ms, and the whilst on tour that the explanation extraction that utilizes manual mode of dividing surface structure to carry out near surface structure velocity layering position calculates after handling is 28.2ms.Owing to also there is the error of fitting that to expect among these two particularly manual interpretation processes of time, so when interpretation results contrasts, also there is the error about 2.9ms, that is to say, on the application as the near-surface investigation achievement, using certain some degree of depth velocity structure of the model section that method of the present invention obtains is equivalent with the manual degree of depth velocity structure of explaining that the back single-point is divided.

Table 1 utilizes explanation results of the present invention and the contrast of conventional layering explanation results

By above description as can be seen, the method of investigation surface structure provided by the invention, adopted chromatography conversion method to obtain the top layer rate pattern, can break away from the restriction of execution conditions and cost in the conventional surface structure investigation method, data acquisition and construction are relatively more convenient, the near surface structure quantity of information that obtains is than little refraction, the micro logging method is abundant, be particularly useful for topographic relief and reach the zone that surface structure thickness wishes to spend more drilling costs more greatly and not more greatly, as the loess tableland district etc., and method provided by the invention can obtain to explain that with conventional micro logging the higher near-surface model of the precision of equivalence describes achievement.

Claims (7)

1. method of investigating surface structure, this method comprises:

(a) from the seismic data of gathering, extract the primary wave real travel time, and form the real travel time matrix along a plurality of seismic traces of seismic line;

(b) obtain being used to reflect the speed matrix or the slowness matrix of surface structure based on chromatography conversion method according to described real travel time matrix;

(c) reflect that based on step (b) being used to of obtaining the speed matrix of surface structure or slowness matrix set up slowness and the depth relationship model that is used to reflect the speed and the depth relationship model of surface structure or is used to reflect surface structure.

2. the method for investigation surface structure according to claim 1, wherein, step (b) may further comprise the steps:

(b1) for given initial velocity matrix or initial slowness matrix, theory of computation whilst on tour matrix and theoretical raypath matrix;

(b2) the theoretical whilst on tour matrix that step (b1) is tried to achieve and theoretical raypath matrix substitution inversion equation Ms=t or M/v=t, obtain new speed matrix or slowness matrix to upgrade initial velocity matrix or initial slowness matrix, wherein M is the raypath matrix, t is the whilst on tour matrix, s is the slowness matrix, v is the speed matrix, s=1/v; With

(b3) based on new speed matrix or the slowness matrix obtained in the step (b2), till the root mean square average of the difference between repeating step (b1) and step (b2) each corresponding whilst on tour in theoretical whilst on tour matrix and real travel time matrix was no more than predetermined threshold, speed matrix or the slowness matrix that try to achieve this moment were the speed matrix or the slowness matrix that are used to reflect surface structure that utilizes chromatography conversion method to ask for.

3. the method for investigation surface structure according to claim 1, wherein, described seismic trace evenly distributes on seismic line, and the track pitch of seismic trace is chosen between the 1m to 10m.

4. the method for investigation surface structure according to claim 1, wherein, given initial velocity matrix or initial slowness matrix are set up in the following manner: with the seismic line direction is directions X, with with seismic line direction direction vertically downward be that the Z direction is set up the XZ plane, choosing the directions X length that comprises seismic section to be measured is L, Z direction length is the rectangular area of D, with the straight line of m bar this rectangular area is divided into (n-1) * (m-1) individual rectangular element along the straight line of directions X and n bar along the Z direction, rectangular element is pressed from left to right, serial number from top to bottom, the speed of establishing in each rectangular element is v _jOr slowness is s _j, j=1 wherein, 2 ..., (n-1) * (m-1), then by (n-1) * (m-1) individual speed v _jOr slowness s _jThe matrix of forming is initial velocity matrix or initial slowness matrix.

5. the method for investigation surface structure according to claim 3, wherein, in setting up initial velocity matrix or initial slowness matrix process, n and m choose so that the length x of the directions X of each rectangular element _StepLength z with the Z direction of each rectangular element _StepHalf that all is less than or equal to the seismic trace spacing is as the criterion.

6. the method for investigation surface structure according to claim 5 wherein, is used to reflect that the speed of surface structure and depth relationship model are (v _k, z _k) sequence is right, is used to reflect that the slowness of surface structure and depth relationship model are (s _k, z _k) sequence is right, k=1 wherein, 2 ..., (n-1) * (m-1), z _kFor with speed v _kOr slowness s _kThe corresponding degree of depth, z _k=z _Min+ (INT[k/n-1]+1) z _Step, wherein, z _MinBe the minimum depth value along the straight line of directions X, INT is downward bracket function.

7. according to the method for the described investigation surface structure of arbitrary claim among the claim 1-6, wherein, described predetermined threshold is less than 10ms.

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