CN109765613A - Shale gas recognition methods based on steepest ladder drop prestack Exact Equation fluid inversion - Google Patents
Shale gas recognition methods based on steepest ladder drop prestack Exact Equation fluid inversion Download PDFInfo
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Abstract
The invention discloses a kind of shale gas recognition methods based on steepest ladder drop prestack Exact Equation fluid inversion, construct the objective function based on fluid identification parameter using Zoeppritz equation and porous media petrophysical model, derive inverting iterative equation.The limitation that prestack inversion avoids low-angle brought by Zoeppritz approximate expression is directly carried out using Zoeppritz equation, and the seismic data of wide-angle is preferably utilized；Convergence efficiency is improved using steepest ladder drop algorithm, reduces calculation amount.The estimated value of fluid identification parameter can be quickly and accurately obtained using the Zoeppritz equation steepest ladder drop inverting of non-reduced, to provide shale gas fluid identification more reliable foundation.
Description
Technical field
The present invention is based on the shale gas recognition methods of steepest ladder drop prestack Exact Equation fluid inversion, belong to oil-gas exploration skill
Art field.
Background technique
Although common poststack seismic inversion can solve the problems, such as the spatial of reservoir under certain condition,
But there is obvious deficiency in the prediction of complex oil and gas reservoir thin for longitudinal thickness, cross directional variations are big and description problem, because of water
The seismic data obtained after flat superposition makes the AVO characteristic of echo amplitude disappear, it is also possible to many vacations for causing amplitude to explain
As；Information and some subtle stratum characteristics all will weaken and disappear when amplitude abundant that pre stack data is included and travelling,
Especially when the thickness of reservoir itself is much smaller than the resolution capability of earthquake, post-stack inversion is difficult to determine the accurate position of reservoir
It sets.Pre-stack seismic inversion remains the feature that seismic reflection amplitude changes with offset distance or incidence angle, it is possible to provide more, quicker
Feel effective data volume achievement, under the constraint of well logging information, carries out earthquake P- and S-wave velocity and density and other elastic parameters
Pre-stack seismic inversion research, a variety of elastic parameters for calculating and obtaining high-precision, can reflect reservoir variation, oil complicated for research
The spatial distribution of gas reservoir, development have a very important significance fine description of complex reservoir etc..
Therefore, using earthquake data before superposition abundant, under the constraint of well logging information, it is anti-to carry out pre-stack seismic elastic parameter
It drills, obtains P- and S-wave velocity and density high-precision, that be able to reflect reservoir cross directional variations, and on this basis, indulged
Wave profile, S-wave section, longitudinal wave and shear wave relative velocity section, longitudinal wave and shear wave absolute velocity profile (eliminate low frequency shadow
Ring), P-S wave velocity ratio section, Poisson's-ratio section, gas-bearing formation instruction section and intercept and slope product section, fluid factor section
Deng, provide more information for geologists, may be implemented the quantitative forecast to oil and gas reservoir, reduce multi-solution, mention
High drilling success reduces exploration risk.For studying the spatial distribution of complex oil and gas reservoir, carry out the essence to complex reservoir
Fluid properties etc. in thin description and identification reservoir are all highly beneficial.
Pre-stack seismic inversion is based on nonzero-offset seismic data, remains Seismic Reflection Amplitude with offset distance or incidence
The feature of the variation at angle, it is possible to provide more, more sensitive effective data volume achievement.Pre-stack seismic P- and S-wave velocity and density etc.
Multi-parameter joint inversion can obtain geophysical parameters that are high-precision, being able to reflect reservoir cross directional variations, this is multiple for studying
The spatial distribution of miscellaneous oil and gas reservoir, development all have a very important significance fine description of complex reservoir etc..In order to incite somebody to action
The problem of Elastic Wave Inversion problem reduction is approximately more easy solution, current prestack inversion technology generally use
The approximate expression of Zoeppritz equation records estimation rock by actual seismic trace gather according to amplitude with the variation relation of incidence angle
The seismologic parameter of stone.But practical problem is difficult to meet the condition that the approximate expression of Zoeppritz equation is set up, i.e., in low-angle
In range, as long as the formation parameter variation of two layers of medium is slightly larger, this approximation will generate in iterative process repeatedly
Certain calculating error.On the other hand, for the approximate simplified style of Zoeppritz equation when wide-angle calculates, application condition is big,
It is difficult to improve the inversion accuracy of wide-angle seismic data, is not able to satisfy the Geologic Requirements of exploration and development, needs to find more accurately
Inversion Calculation method.
The exception related with pore-fluid feature that fluid factor is substantially established under rock physics theoretical direction is special
Property characterization, rely on fluid factor sentence knowledges of the reservoir containing fluid type may be implemented, wherein fluid factor building is realization reservoir stream
The key technology of body identification.Prestack AVO inverting is to extract one of the effective way of fluid factor, and basis is the side Zoeppritz
Journey, but do not overcome approximate bring negative effect-wide-angle error big.In addition, existing inverting, which solves, mainly uses line
Property solves, and ignores high-order term, error is big；And non-linearization solution is computationally intensive.Current fluid identification is all indirect method,
I.e. first inverting elastic parameter calculates fluid parameter by rock physics equations, and indirect method calculates complexity, exists simultaneously accumulated error,
Cause fluid identification multi-solution strong, it is difficult to meet unconventional oil and gas-shale gas fluid identification demand, need to find and overcome AVO
Inversion error and computationally intensive and indirect method obtain the strong inversion technique of fluid multi-solution.
It is therefore proposed that the prestack Exact Equation fluid direct inversion technology based on steepest ladder drop is directly to utilize
Zoeppritz equation accurately solves and porous media petrophysical model directly carries out prestack fluid parameter inverting, preferably utilizes
The Prestack seismic data of wide-angle is based on petrophysical model, can accurately obtain shale gas fluid identification parametric inversion
Inversion result, to provide more reliable foundation for shale gas fluid identification.
The prior art one related to the present invention
Post-stack inversion, which refers to, seeks reflection coefficient by the seismic data by horizontal superposition, recycles wave impedance and reflection system
Relationship between number converts reflection coefficient to the inversion method of wave impedance.
During post-stack inversion, seeking corresponding reflection by the seismic data of level superposition first with the Method of Deconvolution is
Number R, then by
In formula, AIi+1=ρi+1Vpi+1、AIi=ρiVpiRespectively i+1 layer, i-th layer of stratum wave impedance, ρi+1、ρiPoint
Not Wei i+1 layer, i-th layer of stratum density, Vpi+1、VpiRespectively i+1 layer, i-th layer of stratum velocity of longitudinal wave.
Utilize the recurrence relation of the available wave impedance of formula (a):
In formula, ρ1、Vp1The density on respectively the 1st layer stratum, velocity of longitudinal wave.
The wave impedance value that reflection coefficient seeks each stratum can use by formula (2), then carry out reservoir space distribution and pre-
It surveys.
The shortcomings that prior art one: post-stack inversion theoretical method and practical application are all very mature, although certain
Under geological conditions, post-stack inversion can solve the lateral prediction problem of reservoir, but it there is also certain limitations:
The seismic data as used in post-stack inversion is by the data of horizontal superposition, it makes the AVO of echo amplitude
Characteristic disappears, it is also possible to many illusions for causing amplitude to explain, the complex oil and gas reservoir especially thin to thickness, cross directional variations are big
Prediction and description problem Shortcomings.
By above formula (b) it is found that the inversion result of post-stack inversion can only obtain the less elasticity such as wave impedance or velocity of longitudinal wave
The problems such as parameter, they can only simply predict reservoir, and there is multi-solutions, uncertainty.
The prior art two related to the present invention
Current prestack inversion method is all the approximate formula using Zoeppritz equation, according to amplitude and incidence angle
AVO relationship is sought the side of the elastic parameter on each stratum in underground by the angle gathers seismic data of the AVO feature of reflection echo amplitude
Method.
The target of prestack inversion is that the earthquake record of the synthetic seismogram and actual measurement that are obtained using convolution formula is carried out pair
Than keeping the minimal error of the two minimum, even if the value of objective function is minimum, the objective function is expressed as follows:
In formula, wherein V=[Vp, Vs, ρ], Vp, Vs and ρ are respectively P- and S-wave velocity and density, and D is real seismic record
(angle gathers record), S (V) '=W*R (V) are the earthquake record of synthesis, and W is seismic wavelet, and R (V) is with Zoeppritz equation
Approximate formula calculate reflection coefficient.
The approximate formula of currently used Zoeppritz equation has:
1) Aki-Richard approximate formula:
Aki and Richard in 1980 simplify to Zoeppritz equation, is approximate, has been obtained opposite when elastic parameter
VariationWhen smaller, change the reflection coefficient indicated relatively with velocity of longitudinal wave, shear wave velocity and density
Formula, it may be assumed that
In formula, Vp, Vs, ρ are respectively the average value of the velocity of longitudinal wave of interface two sides, shear wave velocity and density, Δ Vp, Δ
Vs, Δ ρ are respectively the difference of the velocity of longitudinal wave of interface two sides, shear wave velocity and density, and θ is the incidence angle and transmission of incident longitudinal wave
The average value of the angle of transmission of longitudinal wave.
2) Shuey approximate formula
Shuey in 1985 introduces Poisson's ratio and does to zoeppritz equation on the basis of Aki-Richard approximate formula
Further simplification, approximation, are deduced:
In formula,
In formula, Vp, ρ, σ are respectively the average value of the velocity of longitudinal wave of interface two sides, density and Poisson's ratio, Δ Vp, Δ ρ, Δ σ
The respectively difference of the velocity of longitudinal wave of interface two sides, density and Poisson's ratio, θ be incident longitudinal wave incidence angle and transmitted P-wave it is saturating
The average value of firing angle.
Reflection coefficient formula in formula (e), which can be regarded as, to be consisted of three parts, respectively low-angle, middle angle and big angle
Degree three, when incidence angle is smaller, usually can be omitted the Section 3 in formula (e), i.e. wide-angle item, obtains two shuey
Approximate formula:
The shortcomings that prior art two:
Currently used prestack inversion is realized using the approximate formula of Zoeppritz equation, such as Aki&Richard
Formula, Shuey formula etc., they calculate easy, it is easy to accomplish, but derived by the accurate solution of Zoeppritz equation approximate public
It is all when incidence angle is smaller when formula, it is assumed that obtained under the premise of the opposite variation less of the elastic parameter of adjacent earth formations various
Approximate formula when only meeting these conditions, is only accurately using the prestack inversion that various approximate formulas carry out.But it is practical
Geological condition be difficult to meet these conditions, as long as the formation parameter variation of two layers medium is slightly larger, it is this it is approximate repeatedly repeatedly
For certain calculating error will be generated in calculating process.And the approximate simplified style of Zoeppritz equation is calculated in wide-angle
When, error is also bigger, it is difficult to and the inversion accuracy of wide-angle seismic data is improved, is not able to satisfy the Geologic Requirements of exploration and development,
Need to find more accurate Inversion Calculation method.
The prior art three related to the present invention
The calculation of the common fluid factor mostly indirect combinatorial operation based on elastic parameter at this stage.Utilize seismic data
The type and characteristic of study of rocks pore cell institute fluid storage, will be with reservoir fluid usually under rock physics theoretical direction
Related abnormal characteristic is characterized as fluid factor, then fluid factor is relied on to realize that the type of medium pore-fluid sentences knowledge.
The prestack elastic parameter inversion being primarily based in technology two obtains elastic parameter；Secondly, utilizing fluid parameter and bullet
Property parameter rock physics equations, fluid identification parameter is calculated indirectly by mathematic(al) manipulation, finally, using indirectly calculating obtain
The fluid identification parameter prediction fluid distrbution feature obtained.In view of seismic inversion problem inherently " morbid state solution " and " more
The problems such as solution property ", it is impossible that the accurate solution of reservoir elastic parameter is obtained just with seismic data inverting.Therefore, it is based on
These elastic parameters inevitably will cause in calculating process by the fluid factor of indirect algebraic combination and calculate error
Accumulation improves inverting quality, it is necessary to needle to preferably effectively be combined prestack seismic inversion method with fluid identification
Carry out the inversion method research after AVO reflectivity model parametrization to fluid factor.
The shortcomings that prior art three
The quality of such fluid identification depends primarily on two aspects, first is that whether participate in the elastic parameter calculated reliable；Two
Be building fluid factor it is whether sensitive to pore-fluid type and stablize.In view of pre-stack seismic inversion is to extract foundation elasticity
The main means of parameter can preferably improve elastic parameter reliability by improving inversion method；In addition, solid by earthquake indirect problem
" the morbid state solution " that has etc. is uncertain to be influenced, and inevitably will cause cumulative errors based on the fluid factor combined indirectly.
Summary of the invention
To solve the shortcomings of the prior art, the invention discloses drop prestack Exact Equation fluid inversion based on steepest ladder
Shale gas recognition methods, this method directly carries out prestack inversion using Zoeppritz equation, avoids Zoeppritz approximation
The seismic data of wide-angle is preferably utilized in the limitation of low-angle brought by formula, improves convergence using steepest ladder drop algorithm
Efficiency reduces calculation amount, so the Zoeppritz equation steepest ladder drop inverting using non-reduced can quickly and accurately obtain fluid
The estimated value of identification parameter, to provide shale gas fluid identification more reliable foundation.
The invention is realized by the following technical scheme:
Shale gas recognition methods based on steepest ladder drop prestack Exact Equation fluid inversion, comprising the following steps:
Step 1: it is based on convolution model and Zoeppritz establishing equation objective function, to objective function Taylor expansion and is changed
Letter introduces the seismic data of multiple angles, forms a joint equation group, establishes changing for joint equation group with bayesian theory
For formula, the parameter in equation group is sought by equivalencing based on snell law, obtains inversion matrix；
The step 1 obtains the side of inversion matrix based on convolution model and Zoeppritz establishing equation inversion objective function
Method is as follows:
Step 1 is based on convolution model and the following target of Zoeppritz establishing equation according to the thinking of generalized linear inversion
Function:
In formula, VpIndicate velocity of longitudinal wave, VsIndicate that shear wave velocity, ρ indicate density, Vp、Vs, ρ be three elastic parameters, D
For practical angle gathers record, i indicates i-th iteration,It is responded for expectation earthquake model,
S(Vp,Vs,ρ)Δ=W*R (Vp,Vs,ρ) (2)
In formula, R (Vp,Vs, ρ) and for using the longitudinal wave reflection coefficient of Zoeppritz equation calculation, W is seismic wavelet；
Step 2, willS (the V at initial model responsep,Vs,ρ)iTaylor expansion, and save second order higher order term
It obtains:
In formula,WithSeismic data is respectively indicated to velocity of longitudinal wave, shear wave velocity, density
Partial derivative summation, Δ ρkIndicate that the density contrast of kth layer with k-1 layers, k indicate k-th of data point；
(3) formula is substituted into (1), seeks Δ V to (1) both ends by step 3p, Δ VsWith the single order local derviation of Δ ρ and to enable it be zero,
Enable Δ di=D (Vp,Vs,ρ)i-S(Vp,Vs,ρ)i, then have:
Due toWithIt cannot be zero, so having:
The seismic data for introducing multiple angles carrys out these three parameters of joint inversion；Using the angle gathers of large, medium and small three angles
Data are respectively as follows: low-angle D1, middle angle D2 and wide-angle D3, with G (vp) replaceWith G (vs) replace
With G (ρ) replacementThen (7) formula turns to:
-Δd1+G1(vp)Δvp+G1(vs)Δvs+G1(ρ) Δ ρ=0 (8)
-Δd2+G2(vp)Δvp+G2(vs)Δvs+G2(ρ) Δ ρ=0 (9)
-Δd3+G3(vp)Δvp+G3(vs)Δvs+G3(ρ) Δ ρ=0 (10)
(8), (9), (10) three formulas are written as matrix form are as follows:
According to (11), the expression formula of Perturbation can be obtained using least square method are as follows:
Δ m=[GTG+λI]-1GTΔd (12)
Due to element G (v in matrixp) beG(vs) beG (ρ) isAndPass through solutionWithJust G (v is acquiredp), i.e.,
Obtain the expression of Jacobian matrix element；It solves equation (11), obtains the parameter i.e. inversion result in equation.
The partial derivative of three elastic parameters (Vp, Vs, ρ) obtains by the following method:
By Zoeppritz equation inference reflection coefficient to the partial derivative of each parameter
It is as follows that Zoeppritz equation is written as matrix form:
AR=B (13)
Wherein A, R, B are respectively as follows:
In formula, α1For incident compressional angle, α2For shear wave incidence angle, β1For longitudinal wave angle of transmission, β2For shear wave angle of transmission, TpIt is vertical
Wave transmission coefficient, TsFor shear wave transmission coefficient；
Utilize Snell's law:Use α1Converse the α in coefficient matrices A and B2、
β1And β2Element, that is, have:
Above formula is brought into (14) and (15) formula, is obtained:
Enable m=(VPi, VSi, VPi+1, Vsi+1, ρi+1, ρi), by (13) both sides respectively to each component, that is, V in mPi, VSi,
VPi+1, Vsi+1, ρi+1And ρiPartial derivative is asked to obtain:Wherein miFor i-th of component in m, i.e.,
It calculates:Reflection coefficient can be obtained to the partial derivative of each parameter by solving equation (18):
It is obtained by (13) formula:
R=A-1B (20)
(20) are brought into (19), are obtained:
A and B is solved individually below to the partial derivative of each parameter, withWithFor:
Step 2: acquisition elastic parameter and physical parameter establish petrophysical model；Based on petrophysical model, building
Fluid factor；Elastic parameter based on inverting, according to porous media petrophysics equation, by elastic parameter and physical parameter it
Between converted, obtain the inversion matrix expression formula based on physical parameter；
Step 3: by the inversion matrix that step 1 obtains and the page that step 2 is obtained based on porous media petrophysical model
Rock air-sensitive sense recognition factor (λ ρ) combines, and reflection coefficient of the building based on the fluid identification factor accurately solves inversion equation expression
Formula；
The method that the reflection coefficient of the building based on the fluid identification factor accurately solves inversion equation expression formula is as follows:
It is preferred that shale gas fluid identification sensitive factor, is based on porous media rock physics equations, elastic parameter and stream are built
The mathematics conversion formula of body recognition factor:
In known 38 kinds of parameters in the elasticity and physical parameter most close with Hydrocarbon Relationship, following four ginseng is selected
Number:②λρ；4. ρ μ, according to specific geological conditions and
Petrophysics property analyzes conclusion to determine, but there is also difference, which parameters in the applicable cases of four parameters in different regions
It is most strong to the sensibility of oil gas, it is still necessary to analyzed based on practical physical test of rock parameter, for shale gas λ ρ because
Sub- applicability is most strong.
For shale gas, λ rho factor is selected, is based on porous media rock physics,By mathematic(al) manipulation,
Establish λ ρ and Vp、VsWith the relational expression of ρ:
Formula (25) and (22), (23), (24) simultaneous are obtained based on Vp、VsIt is accurately solved instead with the novel Zoeppritz of λ ρ
Drill equation expression formula.
Step 4: carrying out direct inversion to fluid recognition factor using the steepest escalator method, to shale gas reservoir containing fluid and
Gas-bearing property is analyzed, and makes overall merit to oil and gas and water distribution feature in conjunction with geology and geophysical information.
In gradient descent method:
When n is very big, all f are iterated to calculate every timeiIt can be very time-consuming.
Steepest ladder drop is exactly to exist every timeIn randomly select one calculate replace it is as aboveIt is randomly selected with this
Direction of the direction as decline.
Due toAs selection step-length ηtWhen=O (1/t), algorithm is under desired meaning
Convergence.
Steepest ladder drop be updated by each sample come iteration it is primary, if situation that sample size is very big (such as tens
It ten thousand), then can be only with wherein tens of thousands of or thousands of samples, so that it may iterate to optimal solution, compare under common gradient
Drop method, training speed is obviously accelerated fastly, to accelerate convergence rate, improves inverting efficiency.
Compared with the prior art, the invention has the following beneficial effects:
Accurately solution has derived folding comprising the fluid identification factor for present invention application rock physics equations and Zoeppritz equation
The shale gas Direct Recognition method of preceding Exact Equation inverting improves accuracy of identification.
Steepest ladder drop be updated by each sample come iteration it is primary, if situation that sample size is very big (such as tens
It ten thousand), then can be only with wherein tens of thousands of or thousands of samples, so that it may iterate to optimal solution, compare under common gradient
Drop method, training speed is obviously accelerated fastly, to accelerate convergence rate, improves inverting efficiency.
The present invention improves inverting efficiency using steepest ladder drop, and the trial result shows significant effect, and differentiation storage can be effectively predicted
The property of layer, high-precision identify shale gas enrichment region, carry out oil and gas detection processing using the present invention, can guarantee computational accuracy
While, rapidly and efficiently, greatlys save and calculate the time, there is good practical application value.
Detailed description of the invention
Following further describes the present invention with reference to the drawings.
Fig. 1 is the method for the present invention flow chart；
Fig. 2 is that prestack Exact Equation fluid inversion fluid detection result drops in steepest ladder；
Fig. 3 is based on three parametric inversion fluid detection result figure of prestack；
Fig. 4 is poststack fluid detection, indirect fluid detection and direct fluid detection comparative result figure.
Specific embodiment
The present invention is described in further detail combined with specific embodiments below, but protection scope of the present invention is not
Be limited to these embodiments, it is all without departing substantially from the change of present inventive concept or equivalent substitute be included in protection scope of the present invention it
It is interior.
According to the shale gas recognition methods based on steepest ladder drop prestack Exact Equation fluid inversion of proposition, to Baojing area
The practical Prestack seismic data of shale gas reservoir carries out the application study of fluid detection.
Work area overview
Hunan Baojing shale gas block main body is located in Baojing County, Hunan Province, and exploration area is 1189.72km2, the earth structure
It makes and is located at the western edge Hunan west place in Hubei separate slot formula thrust-fold belt of middle Yangtze paraplatform, deposition characteristics, which are controlled by Middle Yangtze region construction, drills
Change.Middle Yangtze region is formed after jinning movement stablizes platform, and hinterland continued access is deposited.It is big from the Sinian Period to Early Ordovician Epoch
Type megagea cratonic basin is in tension type passive continental margin environment, deposited the carbonate formation of huge thickness；It is early to the Silurian Period
Phase, under the control of global Caledonian tectonic movement, middle southeastern margin of the Yangtze platform polymerize with China plate, variable phase, in the western Hunan
Area forms foreland basin, deposited huge thick-layer marine facies flysch.Especially it deposited stagnant basin black mud in Longmaxian Age
Shale, organic composition content is higher, is a set of important hydrocarbon source rock series of strata, and the even entire Yangtze area shale in research area
The main interval of gas exploration；Hai Xi-Indosinian movement early stage, by the control of Paleotethys rifting, Middle Yangtze region intermittence
Tension rift, down warping region form sedimentary basin, and Xiangxi Region deposited Devonian system clastic rock and the Permian System-Lower Triassic Series carbonate
Rock bed succession；To Indosinian movement advanced stage, Yangtze craton and North China Plate collision-join, Middle Yangtze region finish marine deposit
History, western Hunan most area uplift erosion.After Yanshanian movement, the main-body structure screen work of Yangtze craton, Hunan have been established substantially
All lifting is swelled in western area, forms mountain topography now.Wherein Longma small stream group richness organic matter mud shale is important page
Rock gas exploration layer position.
According to the shale gas recognition methods based on steepest ladder drop prestack Exact Equation fluid inversion of proposition, to Baojing area
The practical Prestack seismic data of shale gas reservoir carries out the application study of fluid detection.
Step 1: it is based on convolution model and Zoeppritz establishing equation objective function, to objective function Taylor expansion and is changed
Letter introduces the seismic data of multiple angles, forms a joint equation group, establishes changing for joint equation group with bayesian theory
For formula, the parameter in equation group is sought by equivalencing based on snell law, obtains inversion matrix；
Step 2: acquisition elastic parameter and physical parameter establish petrophysical model；Based on petrophysical model, building
Fluid factor；Elastic parameter based on inverting, according to porous media petrophysics equation, by elastic parameter and physical parameter it
Between converted, obtain the inversion matrix expression formula based on physical parameter；
Step 3: by the inversion matrix that step 1 obtains and the page that step 2 is obtained based on porous media petrophysical model
Rock air-sensitive sense recognition factor (λ ρ) combines, and reflection coefficient of the building based on the fluid identification factor accurately solves inversion equation expression
Formula；
Step 4: carrying out direct inversion to fluid recognition factor using the steepest escalator method, to shale gas reservoir containing fluid and
Gas-bearing property is analyzed, and makes overall merit to oil and gas and water distribution feature in conjunction with geology and geophysical information.
Shale is implemented in the shale gas identification based on steepest ladder drop prestack Exact Equation fluid inversion proposed according to the present invention
Air-flow body Direct Recognition is simultaneously compared with conventional method, and it is specific to be substantially better than Common fluids recognition methods for new method effect as the result is shown
As a result as in Figure 2-4, Fig. 2 be based on steepest ladder drop prestack Exact Equation fluid inversion testing result, it can be seen from the figure that
It is distributed interval in shale, has certain shale gas to show；Fig. 3 is the p-and s-wave velocity obtained based on three parametric inversion of prestack and close
Degree, the fluid detection result calculated by rock physics relations, it can be seen that there is fluid to show up and down in shale section, and
The well beyond distribution of shale.Comparison it can be seen that steepest ladder drop prestack Exact Equation fluid inversion result precision and
Resolution ratio is apparently higher than three parameter indirect fluid inversion result of prestack, can embody the advance for originally researching and proposing method.Fig. 4 is
The poststack fluid detection based on fluid activity attribute of another well profile of making a slip of the tongue, the detection of prestack elastic parameter inversion indirect fluid,
Prestack Exact Equation fluid inversion testing result drops in steepest ladder, has page in Longma small stream group 1059.6m-1071.2m depth bounds
Rock gas-bearing formation, first two method is set in well location excessively and is shown without fluid, and has apparent fluid to show originally researching and proposing method,
It can be seen that first two method fluid detection principle limitation, comparison it can be seen that originally research and propose method advance and
Practicability.
The target letter based on fluid identification parameter is constructed using Zoeppritz equation and porous media petrophysical model
Number derives inverting iterative equation.Prestack inversion is directly carried out using Zoeppritz equation avoids Zoeppritz approximate expression institute
The seismic data of wide-angle is preferably utilized in the limitation of bring low-angle；Convergence efficiency is improved using steepest ladder drop algorithm,
Reduce calculation amount.Fluid identification parameter can be quickly and accurately obtained using the Zoeppritz equation steepest ladder drop inverting of non-reduced
Estimated value, to provide shale gas fluid identification more reliable foundation.
The present invention is not limited by embodiment illustrated herein, and is to fit to and principles disclosed herein and novelty
The consistent widest range of feature.
Claims (4)
1. the shale gas recognition methods based on steepest ladder drop prestack Exact Equation fluid inversion, which is characterized in that including following step
It is rapid:
Step 1: being based on convolution model and Zoeppritz establishing equation objective function, to objective function Taylor expansion and abbreviation,
The seismic data for introducing multiple angles forms a joint equation group, and the iteration of joint equation group is established with bayesian theory
Formula is based on snell law, seeks the parameter in equation group by equivalencing, obtain inversion matrix；
Step 2: acquisition elastic parameter and physical parameter establish petrophysical model；Based on petrophysical model, fluid is constructed
The factor；Elastic parameter based on inverting, according to porous media petrophysics equation, by between elastic parameter and physical parameter into
Row conversion, obtains the inversion matrix expression formula based on physical parameter；
Step 3: by the inversion matrix that step 1 obtains and the shale gas that step 2 is obtained based on porous media petrophysical model
Sensitive recognition factor (λ ρ) combines, and reflection coefficient of the building based on the fluid identification factor accurately solves inversion equation expression formula；
Step 4: direct inversion is carried out to fluid recognition factor using the steepest escalator method, fluid and gassiness are contained to shale gas reservoir
Property is analyzed, and makes overall merit to oil and gas and water distribution feature in conjunction with geology and geophysical information.
2. the shale gas recognition methods according to claim 1 based on steepest ladder drop prestack Exact Equation fluid inversion,
It is characterized in that, in the step 1, inversion matrix is obtained based on convolution model and Zoeppritz establishing equation inversion objective function
Method it is as follows:
Step 1 is based on convolution model and the following objective function of Zoeppritz establishing equation according to the thinking of generalized linear inversion:
In formula, VpIndicate velocity of longitudinal wave, VsIndicate that shear wave velocity, ρ indicate density, Vp、Vs, ρ be three elastic parameters, D is real
Border angle gathers record, i indicate i-th iteration,It is responded for expectation earthquake model,
S(Vp,Vs,ρ)Δ=W*R (Vp,Vs,ρ) (2)
In formula, R (Vp,Vs, ρ) and for using the longitudinal wave reflection coefficient of Zoeppritz equation calculation, W is seismic wavelet；
Step 2, willS (the V at initial model responsep,Vs,ρ)iTaylor expansion, and save second order higher order term and obtain:
In formula,WithRespectively indicate seismic data to velocity of longitudinal wave, shear wave velocity, density it is inclined
The summation of derivative, Δ ρkIndicate that the density contrast of kth layer with k-1 layers, k indicate k-th of data point；
(3) formula is substituted into (1), seeks Δ V to (1) both ends by step 3p, Δ VsWith the single order local derviation of Δ ρ and to enable it be zero, Δ is enabled
di=D (Vp, Vs, ρ)i-S(Vp, Vs, ρ)i, then have:
Due toWithIt cannot be zero, so having:
The seismic data for introducing multiple angles carrys out these three parameters of joint inversion；Using the angle gathers number of large, medium and small three angles
According to being respectively as follows: low-angle D1, middle angle D2 and wide-angle D3, with G (vp) replaceWith G (vs) replace
With G (ρ) replacementThen (7) formula turns to:
-Δd1+G1(vp)Δvp+G1(vs)Δvs+G1(ρ) Δ ρ=0 (8)
-Δd2+G2(vp)Δvp+G2(vs)Δvs+G2(ρ) Δ ρ=0 (9)
-Δd3+G3(vp)Δvp+G3(vs)Δvs+G3(ρ) Δ ρ=0 (10)
(8), (9), (10) three formulas are written as matrix form are as follows:
According to (11), the expression formula of Perturbation can be obtained using least square method are as follows:
Δ m=[GTG+λI]-1GTΔd (12)
Due to element G (v in matrixp) beG(vs) beG (ρ) isAndPass through solutionWithJust G (v is acquiredp), i.e.,
Obtain the expression of Jacobian matrix element；It solves equation (11), obtains the parameter i.e. inversion result in equation.
3. the shale gas recognition methods according to claim 2 based on steepest ladder drop prestack Exact Equation fluid inversion,
It is characterized in that, the partial derivative of three elastic parameters Vp, Vs, ρ obtain by the following method:
By Zoeppritz equation inference reflection coefficient to the partial derivative of each parameter
It is as follows that Zoeppritz equation is written as matrix form:
AR=B (13)
Wherein A, R, B are respectively as follows:
In formula, α1For incident compressional angle, α2For shear wave incidence angle, β1For longitudinal wave angle of transmission, β2For shear wave angle of transmission, TpIt is saturating for longitudinal wave
Penetrate coefficient, TsFor shear wave transmission coefficient；
Utilize Snell's law:Use α1Converse the α in coefficient matrices A and B2、β1With
β2Element, that is, have:
Above formula is brought into (14) and (15) formula, is obtained:
Enable m=(VPi, VSi, VPi+1, Vsi+1, ρi+1, ρi), by (13) both sides respectively to each component, that is, V in mPi, VSi, VPi+1,
Vsi+1, ρi+1And ρiPartial derivative is asked to obtain:Wherein miFor i-th of component in m, i.e.,
It calculates:Reflection coefficient can be obtained to the partial derivative of each parameter by solving equation (18):
It is obtained by (13) formula:
R=A-1B (20)
(20) are brought into (19), are obtained:
A and B is solved individually below to the partial derivative of each parameter, withWithFor:
4. the shale gas recognition methods according to claim 1 based on steepest ladder drop prestack Exact Equation fluid inversion,
It is characterized in that, the method that the reflection coefficient of the building based on the fluid identification factor accurately solves inversion equation expression formula is as follows:
It is preferred that shale gas fluid identification sensitive factor, is based on porous media rock physics equations, builds elastic parameter and fluid is known
The mathematics conversion formula of the other factor:
In known 38 kinds of parameters in the elasticity and physical parameter most close with Hydrocarbon Relationship, for shale gas, selection λ ρ because
Son is based on porous media rock physics,By mathematic(al) manipulation, the relational expression of λ ρ Yu Vp, Vs and ρ are established:
Formula (25) and (22), (23), (24) simultaneous are obtained based on Vp、VsInverting side is accurately solved with the novel Zoeppritz of λ ρ
Journey expression formula.
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