CN1132018C - Determine, show and the method for using the relative variation of subsurface rock elastic modulus with density - Google Patents

Abstract

The invention discloses a kind of method of determining, showing and use the relative variation of subsurface rock elastic modulus, can utilize this method searching oil and natural gas with density.Specifically, be the relative variation that utilizes Lame's constant, the relative variation of modulus of shearing and the relative variation and the relation thereof of bulk compressibility modulus, draw and detect factor graph, improved the efficient of seeking oil gas.

Description

Determine, show and the method for using the relative variation of subsurface rock elastic modulus with density

Invention field

The present invention relates to a kind of method of seismic prospecting, particularly, the present invention relates to a kind of method of determining with the relative variation of the relative variation of the elastic modulus of showing subsurface rock and density, and use determined above-mentioned relative variation and show map searching oil and natural gas, particularly directly predict the method for rock gas and lightweight oil.

Background of invention

In the oil-gas exploration the physical parameter of frequent use be speed, the density of rock and the wave impedance of calculating according to their.For finding out the underground structure form, these physical parameters suit.Yet for finding out lithology and direct detection of oil and gas, they will cause uncertainty, because the speed of (1) each rocks and the variation range of density are overlapped each other; (2) too many correlativity is arranged between velocity of longitudinal wave, shear wave velocity, the density, and lack the complementarity of indication lithological change ability aspect.

The elastic modulus of rock comprises Lame's constant λ and μ, bulk compressibility modulus κ, Young modulus E and Poisson ratio σ.They are to introduce physical from material science at first.Their definition mode guarantees that they all are positive numbers.These five elastic modulus are not independently to measure each other.Among them any one can show with two other, can derive a lot of such expression formulas.In the process that wave equation is set up, springform has measured great role.Directly measure normally difficulty of elastic modulus.People are usually according to shear wave velocity, velocity of longitudinal wave and the density calculation elastic modulus measured in the laboratory.

The speed of rock is to be determined by its elastic modulus and density.For example: shear wave velocity Vs and velocity of longitudinal wave Vp can express with density p and elastic modulus

V _s＝(μ/ρ) ^1/2 (1)

V _p＝[(λ2μ)/ρ] ^1/2 (2)

=[(κ+4 μ/3)/ρ] ^1/2(3) in seismic prospecting, the speed of rock on original meaning, only is the expression seismic event is propagated speed in rock physical quantity.The relation of the character of the fluid of filling in the character of speed and rock and the blowhole is indirect.Speed is the result of elastic modulus and density combined influence.Otherwise the character of the fluid of filling in the character of elastic modulus and rock and the blowhole is closer, more direct.Variation has taken place in which or which aspect that the relative variation of each elasticity modulus and the relative variation of density can more directly indicate the character of the character of rock and pore fluid thereof.Therefore, the elastic modulus of determining subterranean strata is very useful for research lithology and direct detection of oil and gas.

At petroleum exploration domain, compressional wave common depth point or common midpoint technology (being designated hereinafter simply as CDP technology or CMP technology) are one of technology that has obtained ten-strike very.In four more than ten years, the CDP technology is among development and the improvement always in the past.Under the assumed condition of horizontal layer stratum,, use the CDP technology can record the seismic data that repeatedly covers by suitable wave detector and shotpoint array.Seismic data to record carries out sorting, can constitute CDP road collection.The seismic trace that the same CDP of superposition road is concentrated with the primary reflection that strengthens from underground same reflection spot, weakens multiple reflection and random noise.Unfortunately, the CDP superposition has also destroyed valuable earthquake information when strengthening primary reflection.And these information are vital for lithology research and direct oil gas detection.

At least since last century end, it has been recognized that on reflecting interface, the reflection amplitude of shear wave and compressional wave changes with incident angle.One of outstanding achievement in research is the Zoeppritz system of equations.This system of equations has been set up the elastic characteristic of reflection coefficient and reflecting interface media of both sides and the relation between the incident angle, (referring to Zeoppritz, K., 1919, " Uber Erbeduellen ", Vol.V, Gottinger Nachrichten, p.66-84).In recent years, people have begun to note utilizing the variation of reflection amplitude with incident angle in oil-gas exploration.People's such as Wiggins european patent application, utilize the variation of amplitude with incident angle, a kind of method of determining and showing subterranean strata shear wave velocity reflection coefficient has been proposed (referring to Wiggins, R., Kenny, G.S.and McMlure, C.D., 1983, " Amethod for determining and displaying theshearvelocityreflectivities of a geologic formation " European Patent ApplicationNo.83300227).Their computing formula is at V _p/ V _sDerive under=2 the assumed condition, this will bring uncertain error to the shear wave velocity reflection coefficient that calculates.Because the shear wave velocity reflection coefficient is insensitive to the character of blowhole fluid, the shear wave velocity reflection coefficient can be used for oil-gas exploration.Also just because of this insensitivity, its effect in oil-gas exploration is limited.The AVO technology is utilized the variation prediction gas reservoir of longitudinal wave reflection amplitude with offset distance, (referring to Ostrander, WJ., 1984, " Plane-wave reflection coefficients for gassands at non-normal angles of incidence Geophysics", Vol.49 is P.1637-1648).It has been found that, in most of the cases, be the gradient that the longitudinal wave reflection amplitude of the saturated sandstone of the gas top of country rock changes with offset distance with shale, and the gradient that changes with offset distance than the longitudinal wave reflection amplitude of the water saturation sandstone top of identical country rock greatly.CDP road collection was as input data before the patented claim of Wigins and AVO technology were all used repeatedly.

Since the CDP technology was born, people had made consistent efforts and have utilized the CDP data to extract velocity of longitudinal wave V _p, the longitudinal wave reflection coefficient, or the like.But, utilize the CDP data to determine the problem of the relative variation of the elastic modulus of subsurface rock or elastic modulus, be a problem of being ignored, seldom being mentioned by seismic prospecting circle by the people.Only in recent years, the problem that just has several authors to mention to utilize the CDP data to determine elastic modulus or their relative variation.People such as Piggott have used a kind of alternative manner to determine Poisson ratio σ.They are by the velocity of longitudinal wave V that is obtained by other data _pAnd density p, utilize iterative algorithm to determine Poisson ratio σ.Then, utilize definite like this Poisson ratio σ and known velocity of longitudinal wave V _pAnd density p, calculate other four elastic modulus and shear wave velocity V _s, (referring to Piggott, J.D., Shrestha, R.K.andWarwich, R.A., 1989, " Young ' s modulus from AVO Inversion ", 59th Annual International SEG Meeting, Expanded Abstracts, p.832-835).It is known that people's such as Piggott alternative manner itself also requires Vp and ρ, and this is unpractical.Silva and Ahmed have used a kind of approximate expression of Zoeppritz system of equations, and Δ κ/κ and Δ μ/κ appear in the equation part as equation coefficient.But they do not manage to determine Δ κ/κ and Δ μ/κ.On the contrary, they by the match amplitude with the change calculations of incident angle the shear wave wave impedance of compressional wave wave impedance and a kind of correction.In itself, their method is identical with the AVO technology.(referring to Sliva, R.And Amhed, H., 1989, " Application of theAVO technique in production geophysics ", 59th Annual International SEG Meeting, Expanded Abstracts, p.836-838).Smith and Gidlow have proposed a kind of ' pseudo-Poisson ratio reflection coefficient ', it equals the velocity of longitudinal wave reflection coefficient and deducts the shear wave velocity reflection coefficient, (referring to Smith, G.C.and Gidlow, P.M., 1987, " Weighted stacking forrock property estimation and detection of gas Geophysical Prospecting", Vol.35, p.993-1014).As if above-mentioned several researchers all do not have really to study to the direction of determining the relative variation of elastic modulus or definite elastic modulus, still the method for seeking to deal with problems in the usual range of physical parameters of using.

The effect of the density of rock in oil-gas exploration is on record.Up to the present, determine that from conventional seismic data the method for density or variable density is that the root-mean-square velocity that earlier velocity analysis is obtained (for example is converted to interval velocity, use the Dix formula to change), re-use empirical relationship (for example, using the Gardner empirical relationship) interval velocity is converted to density.The density poor reliability of Huo Deing does not have use value sometimes at all like this.Utilize conventional compressional wave CDP data directly to determine the density of subsurface rock or the relative variation of density, can improve the reliability of density, and make density that more wide applications be arranged.

In the last thirty years, utilize the hydrocarbon-bearing pool of conventional longitudinal wave earthquake data direct detection is that people pursue always.Many researchists are striving to find the better direct hydrocarbon detection factor.' bright spot ', ' flat spot ', ' dark space ', ' chimney effect ', ' phase change ' are that used several direct hydrocarbon detection factors in the oil-gas exploration before appear in the AVO technology.They have only obtained limited success.The AVO technology provides many direct hydrocarbon detection factors for the scout.Swan has done good summary and discussion to them, (referring to Swan, H.W., 1993, " Properties ofdirect AVO hydrocarbon indicators ", and in Castagana, J.P.and Backus, M.M., Eds., Offset-dependent reflectivity:Theory and Practice of AVo Analysis:SEG) Castagna and Smith at large compared their characteristic, and a new direct hydrocarbon detection factor R is provided _p-R _s, R wherein _pBe compressional wave wave impedance, R _sBe the shear wave wave impedance, (referring to Castagna, J.P.and Smith, S.W., 1994, " Comparisonof AVO indicators:Amodeling study ", Geophysics, Vol.59, p.1849-1855).The direct hydrocarbon detection factor from the AVO technology has reliable theoretical foundation, and the direct hydrocarbon detection factor applied range than early stage has obtained bigger success.Yet, it is found that along with offset distance increases, the pairing longitudinal wave reflection amplitude of the saturated sandstone of gas may increase, and also may reduce.It is very complicated with the factor that offset distance changes to influence amplitude.In addition, the water saturation sandstone also can produce and be similar to the variation with offset distance of amplitude that the saturated sandstone of gas causes.As a rule, it is inconvenient utilizing the direct hydrocarbon detection factor predicting oil of AVO to assemble.Use the AVO technology to carry out direct hydrocarbon detection, existing successful example also has the example of failure.Seek the more effective direct hydrocarbon detection factor and remain research field urgent, that great realistic meaning is arranged.

Goal of the invention

The objective of the invention is to provide the relative variation of a kind of relative variation that utilizes the elastic modulus that seismic data determines subsurface rock and density method, show the method for above-mentioned relative variation and use determined above-mentioned relative variation and show that map seeks oil and natural gas, particularly directly predict the method for rock gas and lightweight oil.Method provided by the invention can help to find out the variation of the character of the variation of character of subsurface rock and blowhole fluid, increases the number of oil-gas exploration target area.By the determined above-mentioned relative variation of method provided by the invention is the direct hydrocarbon detection factor with sturdy rock physics basis, and they can improve the success ratio of direct prediction rock gas and oil effectively.Summary of the invention

The invention provides a kind of method of determining with the relative variation of the relative variation of showing the subsurface rock elastic modulus and density, the relative variation of determined elastic modulus is relative changes delta κ/[κ+(4/3) μ] of relative changes delta mu/(λ+2 μ) of relative changes delta λ/(λ+2 μ), modulus of shearing of Lame's constant and/or Δ μ/[κ+(4/3) μ], bulk compressibility modulus, the relative variation of determined density is Δ ρ/ρ, and this method is made up of the following step:

(a) gather common midpoint or the common depth point seismic data that repeatedly covers, require seismic event as the value of the maximum incident angle of the reflecting interface of the subterranean strata of exploration targets between 30 °～45 °, when having reflection at critical to take place, maximum incident angle should near and less than critical angle;

(b) seismic data is done pre-service, obtain CRP gather through various processing and every correction, make the reflection amplitude of the same time of described each CRP gather, different offset distances with the variation representative of incident angle from the variation of the reflection coefficient of underground same reflection spot, different incidence angles with incident angle;

(c) the same sampling time of estimation also is the incident angle θ of same reflection spot, the incident of different offset distance seismic event; Wherein said incident angle θ is according to calculating the degree of depth of offset distance and reflection spot or reflection interval, and the factor of considering when selecting to calculate the method for θ is the feature complexity of subsurface geological structure;

(d) will be from the reflection coefficient and the corresponding incident angle substitution first linear approximate relationship formula of underground same reflection spot, different offset distance (being same time, same CRP gather); $R\left(\mathrm{\&theta;}\right)\&cong;A(1+{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}+{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/4+B(1-3{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}+{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/2+C(1-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/4$ And/or the second linear approximate relationship formula: $R\left(\mathrm{\&theta;}\right)\&cong;D(1+{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}+{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/4+E(1-5{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}+{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/3+C(1-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/4$ Thereby constitute two overdetermination systems of linear equations, wherein A=Δ λ/(λ+2 μ), B=Δ μ/(λ+2 μ), C=Δ ρ/ρ, D=Δ κ/[κ+(4/3) μ], E=Δ μ/[κ+(4/3) μ];

(e) separate described two overdetermination systems of linear equations respectively, determine coefficient A, B, C and/or D, E, C;

(f) each sampling time to same CRP gather repeats (c), (d), (e) each step;

(g) each CRP gather to same section repeats (c), (d), (e), (f) each step;

(h) coefficient of above-mentioned determined each overdetermination system of linear equations is showed with the plotting mode of single relative variation section, the plotting mode of comprehensive detection section and three kinds of modes such as plotting mode of scatter diagram; The drawing practice of single relative variation section is drawn a sectional view with a coefficient; The drawing practice of comprehensive detection section is three coefficients of same group of overdetermination system of linear equations, according to their numerical symbol positive and negative or greater than syntagmatic less than threshold value, respectively with different colors or symbolic representation it; The drawing practice of two dimension scatter diagram is three coefficients to same group of overdetermination system of linear equations, selects one of them coefficient as parameter, and other two coefficients are respectively as longitudinal and transverse axial coordinate, positive and negative with distinct symbols or color showing parameter; The drawing practice of three-dimensional scatter diagram is that three coefficients with same overdetermination system of linear equations are that three coordinate variables are drawn.

The present invention also provides a kind of use by the determined relative variation of said method and show that map predicts that directly the tax of rock gas and oil deposits the method for position, and this Forecasting Methodology comprises the following steps:

(a) determined above-mentioned relative variation is divided into two groups of direct hydrocarbon detection factors, first group of direct hydrocarbon detection factor is A, B, C, wherein A=Δ λ/(λ+2 μ), B=Δ μ/(λ+2 μ), C=Δ ρ/ρ; Second group of direct hydrocarbon detection factor is D, E, C, wherein D=Δ κ/[κ+(4/3) μ], E=Δ μ/[κ+(4/3) μ], C=Δ ρ/ρ;

(b) determine the experience threshold value of each direct hydrocarbon detection factor;

(c) according to above-mentioned determined each organize three threshold values of the direct hydrocarbon detection factor, according to above-mentioned comprehensive detection section plotting mode, draw the comprehensive detection sectional view;

(d) determine that according to the comprehensive detection sectional view rock gas and the possible tax of oil deposit the position, its method is, when using first group of direct hydrocarbon detection factor, the scope that the relative changes delta mu of modulus of shearing/(λ+2 μ) surrounds less than the combination of its threshold value less than the relative changes delta ρ/ρ of its threshold value, density greater than relative changes delta λ/(λ+2 μ) of its threshold value, Lame's constant λ shows that rock gas and the possible tax of oil deposit the position; When using second group of direct hydrocarbon detection factor, the scope that the relative changes delta mu of modulus of shearing/[κ+(4/3) μ] surrounds less than the combination of its threshold value less than the relative changes delta ρ/ρ of its threshold value, density greater than relative changes delta κ/[κ+(4/3) μ] of its threshold value, bulk compressibility modulus shows that rock gas and the possible tax of oil deposit the position.

Brief Description Of Drawings

Accompanying drawing 1 is the relative variation of 25 the sandstone reservoirs top board reflecting interfaces and the shale～water saturation sandstone reflecting interface modulus of shearing μ of correspondence.

Accompanying drawing 2 is relative variations of 25 the sandstone reservoirs top board reflecting interfaces and the shale～water saturation sandstone reflecting interface Lame's constant λ of correspondence.

Accompanying drawing 3 is relative variations of 25 the sandstone reservoirs top board reflecting interfaces and the shale～water saturation sandstone reflecting interface bulk compressibility modulus κ of correspondence.

Accompanying drawing 4 is relative variations of 25 the sandstone reservoirs top board reflecting interfaces and the shale～water saturation sandstone reflecting interface density p of correspondence.

Accompanying drawing 5 is first group of direct hydrocarbon detection factors A section (being Δ λ/(λ+2 μ)).

Accompanying drawing 6 is first group of direct hydrocarbon detection factor B section (being Δ μ/(λ+2 μ)).

Accompanying drawing 7 is that first group of direct hydrocarbon detection factor C section (is Δ ρ/ρ).

Accompanying drawing 8 is first group of direct hydrocarbon detection factor comprehensive detection section.

Accompanying drawing 9 is first group of direct hydrocarbon detection factor scatter diagram.

Accompanying drawing 10 is first group of direct hydrocarbon detection factor scatter diagram (detecting along layer).

Detailed description of the invention

For the method for the relative variation of clearly illustrating the relative variation of descending elastic modulus of rock definitely provided by the invention and density, reflect when inciding on the reflecting interface of subsurface rock about seismic event in the seismic prospecting that at first makes brief of the introduction, the basic theories of transmission and wave mode conversion.The those of skill in the art of seismic prospecting industry know: when compressional wave impinges perpendicularly on the horizontal reflection interface, only produce reflected P-wave and transmitted P-wave; When compressional wave oblique incidence during to the horizontal reflection interface, except that producing reflected P-wave and transmitted P-wave, also will produce transformed wave is reflection wave and transmitted shear wave; Energy between the various wave modes, i.e. reflection coefficient and transmission coefficient are decided by velocity of longitudinal wave, shear wave velocity, density and the incident angle of reflecting interface both sides rock.The Zoeppritz system of equations has been expressed the relation between velocity of longitudinal wave, shear wave velocity, density and the incident angle of the reflection of various waveforms and transmission coefficient and reflecting interface both sides rock.But in actual applications, accurately complete Zoeppritz system of equations is too complicated, and for finding the solution the needed information of this system of equations generally and do not know.Therefore, multidigit researcher under different assumed condition, has proposed the multiple approximate expression of Zoeppritz system of equations for different research purposes.The approximate expression that Aki and Richards propose be subjected to quoting widely (referring to Aki, K.I.and Richards, P.G., 1980 " Quantitative Seismology ", W.H.Freeman and Co., P.153).The relative variation of elastic characteristic of supposing the reflecting interface media of both sides is smaller, and longitudinal wave reflection coefficients R (θ) can be expressed as: $R\left(\mathrm{\&theta;}\right)=\frac{1}{2}(1-4\frac{V_x^2}{{\mathrm{<figure-callout\; id="2"\; label="V\; p"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">V</figure-callout>}}_p^{}}{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;})\frac{\mathrm{\&Delta;\&rho;}}{\mathrm{\&rho;}}+\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="sec"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sec</figure-callout>}}^2\mathrm{\&theta;}\frac{\mathrm{\&Delta;}{V}_p}{V_p}-4\frac{V_x^2}{{\mathrm{<figure-callout\; id="2"\; label="V\; p"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">V</figure-callout>}}_p^{}}{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}\frac{\mathrm{\&Delta;}{V}_s}{V_s}---\left(4\right)$ Wherein

V _p＝(V _p2+V _p1)/2 ΔV _p＝V _p2-V _p1

V _s＝(V _s2+V _s1)/2 ΔV _s＝V _s2-V _s1

ρ＝(ρ ₂+ρ ₁)/2 Δρ＝ρ ₂-ρ ₁

θ＝(θ ₂+θ ₁)/2

V _P1, V _S1, ρ ₁Be respectively velocity of longitudinal wave, shear wave velocity, the density of covering medium on the interface;

V _P2, V _S2, ρ ₂Be respectively underlie velocity of longitudinal wave, shear wave velocity, the density of medium of interface;

V _p, V _s, ρ is respectively compressional wave average velocity, shear wave average velocity, the average density of interface media of both sides;

θ ₁, θ ₂Be respectively incident compressional angle, refraction angle, θ is the mean value at incident angle and refraction angle.

Because the speed that seismic event is propagated in subsurface rock is to be determined by the elastic modulus of rock and density, the speed in (4) formula can replace with elastic modulus and density.Make λ ₁, μ ₁And κ ₁Cover the elastic modulus of medium in the expression, make λ ₂, μ ₂And κ ₂The underlie elastic modulus of medium of expression makes λ, and μ and κ are respectively:

λ＝(λ ₁+λ ₂)/2

μ＝(μ ₁+μ ₂)/2

κ＝(κ ₁+κ ₂)/2

Because supposed that the relative variation of elastic characteristic of reflecting interface media of both sides is smaller, so and $V_s\&cong;{(\mathrm{\&mu;}/\mathrm{\&rho;})}^{1/2}---\left(5\right)$ $V_p\&cong;{[(\mathrm{\&lambda;}+2\mathrm{\&mu;})/\mathrm{\&rho;}]}^{1/2}---\left(6\right)$ $\&cong;{[(\mathrm{\&kappa;}+4\mathrm{\&mu;}/3)/\mathrm{\&rho;}]}^{1/2}---\left(7\right)$ The approximate establishment is very little percentage with respect to the error of actual mean value.(5), (6) two formulas are got differential: $\frac{\mathrm{\&Delta;}{V}_s}{V_s}=\frac{1}{2}(\frac{\mathrm{\&Delta;\&mu;}}{\mathrm{\&mu;}}-\frac{\mathrm{\&Delta;\&rho;}}{\mathrm{\&rho;}})---\left(8\right)$ $\frac{\mathrm{\&Delta;}{V}_p}{V_p}=\frac{1}{2}(\frac{\mathrm{\&Delta;\&lambda;}+2\mathrm{\&Delta;\&mu;}}{\mathrm{\&lambda;}+2\mathrm{\&mu;}}-\frac{\mathrm{\&Delta;\&rho;}}{\mathrm{\&rho;}})---\left(9\right)$ And ${\left(\frac{V_s}{V_p}\right)}^2=\frac{\mathrm{\&mu;}}{\mathrm{\&lambda;}+2\mathrm{\&mu;}}---\left(10\right)$ Set up.With (8), (9), (10) three formula substitution (4) formulas, after the abbreviation, (4) formula becomes: $R\left(\mathrm{\&theta;}\right)\&cong;A(1+{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}+{\sin }^2\mathrm{\&theta;}{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/4+B(1-3{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}+{\sin }^2\mathrm{\&theta;}{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/2+C(1-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}-{\sin }^2{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/4---\left(11\right)$ Wherein

A＝Δλ/(λ+2μ) (12)

B＝Δμ/(λ+2μ) (13)

C=Δ p/ ρ (14) then gets if replace (6) formula to do similarly to deduce with (7) formula: $\frac{\mathrm{\&Delta;}{V}_p}{V_p}=\frac{\mathrm{\&Delta;\&kappa;}+\frac{4}{3}\mathrm{\&Delta;\&mu;}}{\mathrm{\&kappa;}+\frac{4}{3}\mathrm{\&mu;}}-\frac{\mathrm{\&Delta;\&rho;}}{\mathrm{\&rho;}}---\left(15\right)$ ${\left(\frac{V_s}{V_p}\right)}^2=\frac{\mathrm{\&mu;}}{\mathrm{\&kappa;}+\frac{4}{3}\mathrm{\&mu;}}---\left(16\right)$ $R\left(\mathrm{\&theta;}\right)\&cong;D(1+{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}+{\sin }^2\mathrm{\&theta;}{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/4+E(1-5{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}+{\sin }^2\mathrm{\&theta;}{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/3+C(1-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\mathrm{\&theta;}-{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;})/4---\left(17\right)$ Wherein

D＝Δκ/[κ+(4/3)μ] (18)

E＝Δμ/[κ+(4/3)μ] (19)

C=Δ ρ/ρ is identical with (14) formula.

Seismic data should be done suitable pre-service before substitution (11) and (17) formula are determined coefficient A, B, C or D, E, C.When (11) and (17) formula of derivation, supposed once that the plane compressional wave incided on the horizontal resiliency interface.And the R (θ) in (11) and (17) formula is a reflection coefficient, rather than the convolution of reflection coefficient and seismic wavelet.Pretreated purpose is to make seismic data satisfy above-mentioned assumed condition and requirement as much as possible.In seismic exploration technique, developed a batch system, they can be used for pre-service of the presently claimed invention.Pretreatment process generally includes: (1) amplitude restoration and compensation, purpose are to proofread and correct factors such as how much diffusions, transmission loss, inelastic attenuation to effect on amplitude, and amplitude is with the variation of offset distance; (2) earth's surface-consistent is handled, and purpose is to eliminate factor inconsistencies such as focus, wave detector, shallow surface to effect on amplitude; (3) filtering to be to eliminate random noise and unwanted reflection line-ups, for example, and multiple reflection and converted shear wave; (4) velocity analysis and NMO proofread and correct; (5) excise direct wave and NMO stretching etc.; (6) deconvolution multiple suppression; (7) wavelet compression reduces the influence of thin layer tuning effect to remove seismic wavelet as much as possible.If the assumed condition of underground structure form and HORIZONTAL LAYERED MEDIUM WITH HIGH ACCURACY greatly differs from each other, then use DMO and repeatedly preceding migration technology that common midpoint gather is converted to CRP gather.If the underground structure form must consider that so, CRP gather should be a common reflection surface road collection as three-dimensional structure.

Incident angle is by the decision of the degree of depth of offset distance and reflection spot in essence.Calculate the method for incident angle and should select diverse ways for use according to the complexity difference of underground structure.When underground medium is medium (V at the uniform velocity _pBe constant) time, then

θ=arctg (X/2Z) (20) wherein

Z is the degree of depth of reflecting interface,

X is an offset distance.When the speed of underground medium is the linear function of the degree of depth, promptly

V _p=V ₀During+KZ (21), $\mathrm{\&theta;}=\mathrm{arctg}\left(\frac{4X({\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">V</figure-callout>}}_0+\mathrm{KZ})}{{4\mathrm{<figure-callout\; id="2"\; label="KZ"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">KZ</figure-callout>}}^2+8V_{0}Z-{\mathrm{KX}}^2}\right)---\left(22\right)$ Wherein

K is that dimension is second ^-1Constant,

V ₀Be the speed of degree of depth medium when being zero,

The meaning of Z, X is identical with (20) formula.Speed V in underground medium is horizontal layer and each layer _pDuring for constant, $\mathrm{\&theta;}=\arcsin \left(\frac{{\mathrm{XV}}_p}{V_{\mathrm{rms}}\sqrt{V_{\mathrm{rms}}^2{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="C9619844600241.png"\; state="\{\{state\}\}">t</figure-callout>}}_0^2+X^2}}\right)---\left(23\right)$ Wherein

t ₀Be the reflection interval of zero-offset (vertical incidence),

V _RmsBe root-mean-square velocity,

The meaning of X is identical with (20) formula.When underground medium is more complicated two dimension or three-dimensional medium, need to use ray tracing technique to calculate incident angle.The inventor has at large summed up the method for calculating incident angle under the different situations, (referring to Chen Xinping, 1996, " informal discussion AVO ", China's offshore oil and gas, (waiting to deliver)).

Owing to derive in the process of (11) and (17) two formulas, high-order term (is sin ²θ tg ²θ) be comprised among (11) and (17), therefore, the high-order term of ignoring that (11) and (17) two formulas are used than AVO technology (is sin ²θ tg ²Equation θ) has better precision.Because when incident angle during greater than 25 °, high-order term (is sin ²θ tg ²Influence θ) be can not ignore, and therefore, general restriction incident angle is less than 25 ° when using the AVO technology.It (is sin that the present invention's use comprises high-order term ²θ tg ²(11) θ) and (17) two formulas can expand to less than 45 ° the restriction of incident angle.Because (11) are relevant with the reflectance signature of reflecting interface (being the elastic difference of reflecting interface both sides rock) with the precision of (17) two formulas, the variation range of incident angle is selected between 0 °～30 ° to 0 °～45 ° in actual applications.When reflection at critical took place, incident angle should be less than critical angle.

Use through suitable pretreated seismic data and the incident angle calculated with suitable method, from underground same reflection spot but the different reflective information of offset distance by substitution (11) formula, formation overdetermination system of linear equations.Use the multiple linear regression computing technique to separate this system of equations and determine coefficient A, B and C.Similarly, if (17) formula of use is then determined coefficient D, E and C.In order to reduce the influence of noise, should select the multiple linear regression calculating method that suits, to guarantee the robustness of result of calculation to result of calculation.It is also important that calculation procedure provides parameter with evaluation calculation result's reliability with inform the non-existent situation of linear relationship.

The computing technique of the group of solving an equation (11) and (17) is not limited to multiple linear regression analysis method, and any computing method of separating the multiple linear system of equations can be used.There are the computing method of immunity to be specially adapted to calculating of the presently claimed invention to the bigger measurement data of discrete error.

The method of the above-mentioned determined relative variation of displaying provided by the invention is as follows:

The invention provides three kinds of modes of showing above-mentioned determined relative variation, they are the plotting mode of single relative variation section, the plotting mode of comprehensive detection section and the plotting mode of scatter diagram.

The drawing practice of single relative variation section is with a relative variation, and promptly a coefficient (A, C, D or E) is drawn a sectional view.Single relative variation section can show the variation of the size of a relative variation and rising, reduction.

The drawing practice of comprehensive detection section is three coefficients to same group of overdetermination system of linear equations, according to their numerical symbol positive and negative or greater than syntagmatic less than threshold value, respectively with different colors or symbolic representation it.Three coefficient A, B, C with first overdetermination system of linear equations are example, and positive and negative according to A=Δ λ/(λ+2 μ), B=Δ μ/(λ+2 μ), C=Δ ρ/ρ is with different colours or their positive and negative combination of symbolic representation.For example, represent Δ μ＞0, Δ λ＜0, Δ ρ＜0 with redness; Represent Δ μ＜=0 with blueness, Δ λ＞=0, Δ ρ＞=0, or the like.

Scatter diagram divides two kinds of two and three dimensions.Three coefficients of each overdetermination system of linear equations make up mutually, are painted on the figure.The drawing practice of two dimension scatter diagram is three coefficients to same group of overdetermination system of linear equations, selects one of them coefficient as parameter, and other two coefficients are respectively as longitudinal and transverse axial coordinate, positive and negative with distinct symbols or color showing parameter.For example, when drawing the two-dimentional scatter diagram of three coefficients of first overdetermination system of linear equations, (being Δ ρ/ρ) be parameter, be transverse axis with A (being Δ λ/(λ+2 μ)), is longitudinal axis drawing with B (Δ μ/(λ+2 μ)) to select C.The two-dimentional scatter diagram of the Hui Zhiing situation that to show eight quadrants like this.Three-dimensional scatter diagram is that three coordinate variables are drawn with coefficient A, B, C (perhaps coefficient D, E, C), generally draws colored map, is beneficial to differentiate the diffusing point in eight quadrant spaces.

The drawing space of above-mentioned three kinds of plotting modes can be chosen as horizontal range～time, horizontal range～degree of depth, horizontal range～horizontal range (being the time section), the degree of depth～degree of depth (being degree of depth section), or makes three-dimensional, perspective map;

Coefficient A, B, C, D and the E of Que Dinging can represent the relative variation of elastic modulus of subsurface rock and the relative variation of density like this.In the variation of they and subsurface rock character and the blowhole variation of fluid properties have closely, direct relation.They can be applied in the lithology study of seismology.But their prior purposes are to be used for direct hydrocarbon detection.

Deposit the method for position for the tax of clearly illustrating the prediction of above-mentioned determined relative variation of use provided by the invention and above-mentioned displaying map rock gas and oil, statistical study conclusion relevant rock physics is theoretical and actual measurement rock elasticity parameter data is described below:

In the rock physics field, use the Biot-Gassmann theory that four more than ten years were arranged, (referring to Gassmann, F., 1951, " Elasticwavesthroughapackingofspheres ", and Geophysics, Vol.16, p.673-685).This theory can be expressed as follows simply with equation:

μ=μ _b(24) Wherein

The modulus of shearing of μ=water saturation rock

μ _bThe modulus of shearing of=gas saturated rock (being the modulus of shearing of rock skeleton)

One of Lame's constant of λ=water saturation rock

λ _bOne of Lame's constant of=gas saturated rock (being one of Lame's constant of rock skeleton)

The bulk compressibility modulus of κ=water saturation rock

κ _bThe bulk compressibility modulus of=gas saturated rock (being the bulk compressibility modulus of rock skeleton)

κ _sThe bulk compressibility modulus of the mineral of=formation rock skeleton

κ _fThe bulk compressibility modulus of the fluid of filling in the=blowhole

The factor of porosity of =rock.

(24) formula shows: when the fluid of filling in the blowhole became gas by water, the modulus of shearing of rock was constant.Because the bulk compressibility modulus of gas approaches null value (promptly approaching unlimited compressibility), and the bulk compressibility modulus of water is about 2.32Gpa, therefore, can infer according to (25) formula, when the fluid of filling in the blowhole becomes gas by water, the Lame's constant λ of rock will reduce, and the degree that reduces is decided by the bulk compressibility modulus κ of factor of porosity , gas saturated rock _bBulk compressibility modulus κ with the mineral that constitute rock skeleton _sSimilarly, can infer according to (26) formula that when the fluid of filling in the blowhole becomes gas by water, the bulk compressibility modulus κ of rock also will reduce, the degree that reduces is subjected to the influence of same factor.But because κ=λ+2 μ, the variation of κ is the comprehensive of λ and μ variation.Lame's constant λ and μ are basic elastic modulus, and bulk compressibility modulus κ, Young modulus E and Poisson ratio σ are compound elastic modulus.Although the definition of bulk compressibility modulus κ is clearer and more definite than Lame's constant λ in the mechanics of materials,, as the direct hydrocarbon detection factor, the indicative function of λ is more single, clear and definite than κ.

Gassmann and Biot are when deriving their above-mentioned theory, the form of The structure of rock and hole has been made following hypothesis: rock is isotropic on macroscopic view, be the wavelength of the yardstick (size) of blowhole much smaller than seismic event, make in the half period of seismic event disturbance, in the small size unit that the rock skeleton by pore fluid and encirclement hole constitutes, the stress that the seismic event disturbance is applied in the small size unit can reach new equilibrium state from initial equilibrium conditions; Blowhole communicates with each other, and makes under open condition, and when rock was subjected to uneven stress, pore fluid can flow, and also can be discharged from rock by rock surface; The stress of seismic event disturbance is enough little, the feasible applicable elements that satisfies Hooke's law.When the character of rock does not satisfy above-mentioned assumed condition, certain error is arranged between the prediction of above-mentioned three formulas and the field data.The experimental determination result and the petrological study achievement of lot of rock samples show: for the sandstone of ' pure ', the prediction of above-mentioned three formulas is quite accurate; For the sandstone that certain clay content is arranged, when the fluid of filling in the blowhole became gas by water, the modulus of shearing of rock raise, and Lame's constant λ and bulk compressibility modulus κ obviously reduce, and density p reduces.As long as contain a spot of gas in the blowhole, will cause the obvious reduction of Lame's constant λ and bulk compressibility modulus κ.

What say above is character with a kind of pore filling fluid of rock when changing, the variation of its elastic modulus and density.The storage cap rock combination that the most often runs in the oil-gas exploration is a page mud stone～sandstone.In general, the modulus of shearing of sandstone is greater than the modulus of shearing of page or leaf mud stone.The Lame's constant λ of the saturated sandstone of gas and bulk compressibility modulus κ are generally less than Lame's constant λ and the bulk compressibility modulus κ that covers page mud stone.The density of the saturated sandstone of gas, in most of the cases, less than on cover the density of page mud stone.Fig. 1 to Fig. 4 is the relative variation of elastic modulus of top board reflecting interface of 25 sandstone reservoirs and the relative variation of density.Symbol '+' expression among the figure is corresponding to the variable quantity of the saturated sandstone of page or leaf mud stone～gas, and black box is represented the variable quantity corresponding to page or leaf mud stone～water saturation sandstone.Fig. 1 is the relative variation (being coefficient B and E) of modulus of shearing, can see having only five to be negative value in 25 gas reservoirs.As seen, the increase of modulus of shearing can be indicated the existence of sandstone.Fig. 2 is the relative variation (being coefficient A) of Lame's constant λ, can see, for the saturated sandstone reflecting interface of page or leaf mud stone～gas, have only in 25 gas reservoirs two be on the occasion of, one near null value, all the other all present negative value; For page or leaf mud stone～water saturation sandstone reflecting interface, great majority be on the occasion of or null value, and when it was negative value, the variable quantity of the corresponding saturated sandstone reflecting interface of page or leaf mud stone～gas then presented lower negative value (or the bigger negative value of absolute value).Therefore, the relative variation of the negative value that Lame's constant λ relatively changes with modulus of shearing on the occasion of combining, can indicate sandstone is gas sand.Fig. 3 is the relative variation (being coefficient D) of bulk compressibility modulus, and this figure is similar to Fig. 2.But owing to comprised the variation of λ and μ in the variation of κ, its hydrocarbon indicative function is similar to Lame's constant and have too late.Fig. 4 is the relative variation (being coefficient C) of density, can see, for the saturated sandstone reflecting interface of page or leaf mud stone～gas, have only in 25 gas reservoirs five be on the occasion of, one near null value, all the other all present negative value; For page or leaf mud stone～water saturation sandstone reflecting interface, great majority also are negative values.But the relative variation of the density of the saturated sandstone reflecting interface of page or leaf mud stone～gas is the negative value than page or leaf mud stone～the water saturation sandstone is lower.Therefore, the relative variation of density also has the effect that important indication gas sand exists.The data of velocity of longitudinal wave, shear wave velocity and the density of the water saturation sandstone of page or leaf mud stone, the saturated sandstone of gas and the correspondence thereof of Fig. 1 to Fig. 4 sandstone reservoirs are taken from Castagna, J.P.and Smith, S.W., 1994, " Comparison of AVOindicators:Amodelingstudy " Geophysics, Vol.59, p.1849-1855.

The method that use provided by the invention is deposited the position by the tax of above-mentioned determined relative variation and above-mentioned displaying map prediction rock gas and oil comprises the following steps:

(a) determined above-mentioned relative variation is divided into two groups of direct hydrocarbon detection factors, first group of direct hydrocarbon detection factor is A, B, C, wherein A=Δ λ/(λ+2 μ), B=Δ μ/(λ+2 μ), C=Δ ρ/ρ; Second group of direct hydrocarbon detection factor is D, E, C, wherein D=Δ κ/[κ+(4/3) μ], E=Δ μ/[κ+(4/3) μ], C=Δ ρ/ρ.

(b) rule of thumb determine the threshold value of each direct hydrocarbon detection factor.If because the working level of exploration area is low, can't determine threshold value, then select the threshold value of same group of three direct hydrocarbon detection factors all to equal zero.

(c) according to above-mentioned determined each organize three threshold values of the direct hydrocarbon detection factor, according to above-mentioned comprehensive detection section plotting mode, draw the comprehensive detection sectional view;

(d) determine that according to the comprehensive detection sectional view rock gas and the possible tax of oil deposit the position, its method is, when using first group of direct hydrocarbon detection factor, the relative changes delta mu of modulus of shearing/(λ+2 μ) is greater than its threshold value, the relative changes delta λ of Lame's constant λ/(λ+2 μ) is less than its threshold value, the relative changes delta ρ/ρ of density deposits the position less than scope demonstration rock gas and the possible tax of oil that the combination of its threshold value is surrounded, when using second group of direct hydrocarbon detection factor, the relative changes delta mu of modulus of shearing/[κ+(4/3) μ] is greater than its threshold value, the relative changes delta κ of bulk compressibility modulus/[κ+(4/3) μ] is less than its threshold value, the relative changes delta ρ/ρ of density deposits the position less than scope demonstration rock gas and the possible tax of oil that the combination of its threshold value is surrounded;

When using the direct hydrocarbon detection factor provided by the invention to predict sandstone reservoirs, should be noted that the situation of two kinds of exceptions.When (1) very big or compaction is very low when Porosity of Sandstone, the modulus of shearing of sandstone also may less than on cover the modulus of shearing of page mud stone.Here, the density of sandstone is less; After the inflation, its density less than on cover the density of page mud stone.The hydrocarbon indicative function of density more seems important.(2) when the compaction of sandstone is very high, because the bulk compressibility modulus of rock skeleton is near the bulk compressibility modulus of rock forming mineral, therefore, this class sandstone when gas is saturated Lame's constant λ and the Lame's constant λ during water saturation be more or less the same, and, the Lame's constant λ of the saturated sandstone of this class gas may be still greater than or be approximately equal to the Lame's constant λ that covers page mud stone.Because the situation of these exceptions, the relative variation of the relative variation of the elastic modulus of the saturated sandstone of page or leaf mud stone～gas interface correspondence and density meets the rule of " modulus of shearing μ increase, Lame's constant λ reduction, density p reduce " basically among Fig. 1 to Fig. 4, and can not meet fully.Use the direct hydrocarbon detection factor provided by the invention, investigate the relative variation of elastic modulus and the relative variation of density in vertical direction with level (along layer) direction simultaneously, make full use of three relations that detect between the factor that each organizes the direct hydrocarbon detection factor, can avoid the prediction error.

The feature of page or leaf mud stone～oily saturated sandstone reflecting interface is between the saturated sandstone of page or leaf mud stone～gas and page or leaf mud stone～water saturation sandstone, relevant with oil properties (lightweight oil or viscous crude), need use the direct hydrocarbon detection factor provided by the invention as the case may be.Lightweight oil generally all contains certain volatile ingredient, as long as and contain the obvious reduction that a small amount of gas just is enough to cause Lame's constant λ and bulk compressibility modulus in the rock.The modulus of shearing of the saturated sandstone of oil general also greater than on cover the modulus of shearing of page mud stone.The density of the saturated sandstone of lightweight oil is less than the density of water saturation sandstone.The direct hydrocarbon detection factor provided by the invention can be used in the detection oil reservoir, particularly the lightweight oil reservoir.

In order to improve the success ratio of direct prediction rock gas and oil, should fully utilize all geology that may utilize, physical prospecting, well logging and rock physics data, select threshold value.The factor of determining direct hydrocarbon detection factor threshold value comprises: the achievement in research of background value, rock physics and the well-log information of each relative variation that the reflectance signature of exploration targets, single relative variation section and scatter diagram show.Select a plurality of threshold values, draw corresponding many comprehensive detection sections, the variation that the position is deposited in rock gas that observation post shows and the possible tax of oil helps to select the best tax of rock gas and oil to deposit the position.Use the strong screen drawing function of modern computer workstation, can do above-mentioned observation and selection easily.

Used DIRECT FORECASTING METHOD before the method for direct prediction rock gas provided by the invention and lightweight oil is better than.Method provided by the invention makes the possible variation of people by the various aspects of the general performance-reflection amplitude-acquisition rock property analyzing rock property and property of pore fluid thereof and change and property of pore fluid thereof.Then, deposit according to these variation prediction oil-gas accumulations taxes again.Used any hydrocarbon detection factor before the direct hydrocarbon detection factor that method of the present invention produced is better than.At first, the direct hydrocarbon detection factor provided by the invention is that the variation by direct indication rock property and property of pore fluid thereof comes predicting oil to assemble to compose to deposit, they be really directly Indication of Oil-Gas assemble to compose and deposit.And the former hydrocarbon detection factor is directly to utilize reflection amplitude to predict, for example, what the early stage hydrocarbon detection factor ' bright spot ' was utilized is the strong reflection amplitude; Recent, be respectively zero-offset reflection amplitude and reflection amplitude rate of change based on the hydrocarbon detection factor ' intercept ' of AVO technology and ' gradient ' utilization with offset distance.The second, two groups of hydrocarbon detection factors provided by the invention, three instruction parameters in each group respectively have unique hydrocarbon indicative function to interknit additional again.The increase of modulus of shearing represents that the rock rigidity increases, and is the indication that sandstone or other ragstones exist.The reducing of Lame's constant λ indicates that the blowhole fluid properties changes.The reduction of density further indicates rock porosity to increase and/or pore fluid becomes oil gas by water.The existing direct hydrocarbon detection factor only utilizes the surface of earthquake reflected wave, single feature (for example, amplitude power, phase transition or the like) to provide oil-gas accumulation to compose the evidence of depositing in a certain respect.Two groups of direct hydrocarbon detection factors provided by the invention are directly indicated the variation of lithology, the variation of property of pore fluid and/or the variation of factor of porosity, and they provide oil-gas accumulation to compose many-sided evidence of depositing.The 3rd, the assumed condition of method provided by the invention is identical with the assumed condition of AVO technology, still, has comprised high-order term in the formula that the present invention uses, and has improved precision and to the degree of utilizing of earthquake information.The direct hydrocarbon detection factor provided by the invention is not additional further assumed condition when using; And some hydrocarbon detection factor assumed condition in theory still claims rationally, still, and the additional more assumed condition of having to again in actual applications.The 4th, the plotting mode of the direct hydrocarbon detection factor provided by the invention is directly perceived, eye-catching, various, is convenient to the user detects the factor from a plurality of angles, a plurality of space observation characteristic and variation.

Though in geophysics, use elastic modulus that very long history has been arranged,, mainly be to be used in the theoretical research.The present invention uses elastic modulus from theoretical research parameter becomes the parameter of using in the actual exploration.This will cause the change to a certain degree of oil-gas exploration technology.The effect of rock density in oil-gas exploration is on record.In the past, determine that from seismic data the method for density or variable density is that the root-mean-square velocity that earlier velocity analysis is obtained (for example is converted to interval velocity, use the Dix formula), be converted to density (for example, using the Gardner empirical relationship) according to interval velocity use experience relation again.The density reliability of Huo Deing is very poor like this, can not use sometimes at all.The present invention utilizes seismic data directly to determine the relative variation of rock density.The relative variation of the density of determining according to the present invention will be widely used, and the scope that is not limited in this explanation, address.Application example:

Accompanying drawing 5～accompanying drawing 10 is results of an actual measurement seismic section.This section passes the top of a sandstone reservoirs.The red position of the direct hydrocarbon detection factor comprehensive detection section of first group shown in the accompanying drawing 8 has clearly illustrated the gas reservoir position between 1.4 seconds～1.5 seconds.This characteristic with the detection factor of the relevant position of accompanying drawing 5～accompanying drawing 7 is consistent.Accompanying drawing 9 is per 20 CDP of data between this section 1.0 seconds～2.0 seconds to be clicked a CDP order first group of direct hydrocarbon detection factor scatter diagram being done.Check the diffusing point of this figure second quadrant ρ＜0, indication has the gas tax to deposit.Accompanying drawing 10 is per 10 CDP of data between this section 1.4 seconds～1.5 seconds to be clicked a CDP order the first group of direct hydrocarbon detection factor scatter diagram of being done that detects along layer.Check that this figure can further determine the position of gas.Because accompanying drawing 9 and accompanying drawing 10 engineer's scales are too little, the diffusing point in figure centre is together intensive.

The present invention sets about from prediction lithological change and the variation of blowhole fluid properties owing to reinstated new physical parameter, and the predicting oil gathering is composed and deposited, so effective especially; Realize that method and technology provided by the invention only need work out suitable computer program, utilize existing seismic data or utilize existing seismic data acquisition technology, be equipped with existing seismic data process software and just can realize, so implement especially easily.Thought provided by the invention can be used for the integrated interpretation of acoustic logging, acoustic wave train logging, density logging data, directly detects the position of hydrocarbon zone in the well.

Claims (4)

1. determine the method with the relative variation of the relative variation of showing the subsurface rock elastic modulus and density for one kind, the relative variation of the determined elastic modulus of this method is relative changes delta λ/(λ+2 μ) of Lame's constant, the relative changes delta mu of modulus of shearing/(λ+2 μ) and/or Δ μ/[κ+(4/3) μ], the relative changes delta κ of bulk compressibility modulus/[κ+(4/3) μ], the relative variation of determined density is Δ ρ/ρ, use compressional wave common depth point/common reflection point seismic data when this method is determined above-mentioned relative variation, it is characterized in that this method is made up of the following step:

(a) gather common midpoint or the common depth point seismic data that repeatedly covers, require seismic event as the value of the maximum incident angle of the reflecting interface of the subterranean strata of exploration targets between 30 °～45 °, when having reflection at critical to take place, maximum incident angle should near and less than critical angle;

(b) seismic data is done pre-service, obtain CRP gather through various processing and every correction, make the reflection amplitude of the same time of described each CRP gather, different offset distances with the variation representative of incident angle from the variation of the reflection coefficient of underground same reflection spot, different incidence angles with incident angle;

(c) the same sampling time of estimation also is same reflection spot, the incident angle θ of different offset distance seismic event incident, wherein said incident angle θ is according to calculating the degree of depth of offset distance and reflection spot or reflection interval, and the factor of considering when selecting to calculate the method for θ is the feature complexity of subsurface geological structure;

(d) will be from the reflection coefficient of underground same reflection spot, different offset distances and the corresponding incident angle substitution first linear approximate relationship formula: $R\left(\mathrm{\&theta;}\right)\&cong;A(1+{\sin }^2\mathrm{\&theta;}+{\sin }^2\mathrm{\&theta;}{\mathrm{tg}}^2\mathrm{\&theta;})/4+B(1-3{\sin }^2\mathrm{\&theta;}+{\sin }^2\mathrm{\&theta;}{\mathrm{tg}}^2\mathrm{\&theta;})/2$ $+C(1-{\sin }^2\mathrm{\&theta;}-{\sin }^2\mathrm{\&theta;}{\mathrm{tg}}^2\mathrm{\&theta;})/4$ And/or the second linear approximate relationship formula: $R\left(\mathrm{\&theta;}\right)\&cong;D(1+{\sin }^2\mathrm{\&theta;}+{\sin }^2\mathrm{\&theta;}{\mathrm{tg}}^2\mathrm{\&theta;})/4+E(1-5{\sin }^2\mathrm{\&theta;}+{\sin }^2\mathrm{\&theta;}{\mathrm{tg}}^2\mathrm{\&theta;})/3$ $+C(1-{\sin }^2\mathrm{\&theta;}-{\sin }^2\mathrm{\&theta;}{\mathrm{tg}}^2\mathrm{\&theta;})/4$ Thereby constitute two overdetermination systems of linear equations, wherein A=Δ λ/(λ+2 μ), B=Δ μ/(λ+2 μ), C=Δ ρ/ρ, D=Δ κ/[κ+(4/3) μ], E=Δ μ/[κ+(4/3) μ];

(e) separate described two overdetermination systems of linear equations respectively, really coefficient A, B, C and/or D, E, C;

(f) each sampling time to same CRP gather repeats (c), (d), (e) each step;

(g) each CRP gather to same section repeats (c), (d), (e), (f) each step;

(h) coefficient of above-mentioned determined each overdetermination system of linear equations is showed with the plotting mode of single relative variation section, the plotting mode of comprehensive detection section and three kinds of modes such as plotting mode of scatter diagram; The drawing practice of single relative variation section is drawn a sectional view with a coefficient; The drawing practice of comprehensive detection section is three coefficients to same group of overdetermination system of linear equations, according to their numerical symbol positive and negative or greater than syntagmatic less than threshold value, respectively with different colors or symbolic representation it; The drawing practice of two dimension scatter diagram is three coefficients to same group of overdetermination system of linear equations, selects one of them coefficient as parameter, and other two coefficients are respectively as longitudinal and transverse axial coordinate, positive and negative with distinct symbols or color showing parameter; The drawing practice of three-dimensional scatter diagram is that three coefficients with same overdetermination system of linear equations are that three coordinate variables are drawn.

2. according to the process of claim 1 wherein that the drawing coordinate of described plotting mode is chosen as horizontal range～time, horizontal range～degree of depth, horizontal range～horizontal range, the degree of depth～degree of depth, or make three-dimensional, perspective map.

3. a use is by the determined relative variation of the method for claim 1 and show that map predicts that directly the tax of rock gas and oil deposits the method for position, it is characterized in that this method is made up of the following step:

(a) the determined relative variation of the method for claim 1 is divided into two groups of direct hydrocarbon detection factors, first group of direct hydrocarbon detection factor is A, B, C, wherein A=Δ λ/(λ+2 μ), B=Δ μ/(λ+2 μ), C=Δ ρ/ρ; Second group of direct hydrocarbon detection factor is D, E, C, wherein D=Δ κ/[κ+(4/3) μ], E=Δ μ/[κ+(4/3) μ], C=Δ ρ/ρ;

(b) determine the experience threshold value of each direct hydrocarbon detection factor;

(c) according to above-mentioned determined each organize three threshold values of the direct hydrocarbon detection factor, according to the described comprehensive detection section of claim 1 plotting mode, draw the comprehensive detection sectional view;

(d) determine that according to the comprehensive detection section rock gas and the possible tax of oil deposit the position, its method is, when using first group of direct hydrocarbon detection factor, the scope that the relative changes delta mu of modulus of shearing/(λ+2 μ) surrounds less than the combination of its threshold value less than the relative changes delta ρ/ρ of its threshold value, density greater than relative changes delta λ/(λ+2 μ) of its threshold value, Lame's constant λ shows that rock gas and the possible tax of oil deposit the position; When using second group of direct hydrocarbon detection factor, the scope that the relative changes delta mu of modulus of shearing/[κ+(4/3) μ] surrounds less than the combination of its threshold value less than the relative changes delta ρ/ρ of its threshold value, density greater than relative changes delta κ/[κ+(4/3) μ] of its threshold value, bulk compressibility modulus shows that rock gas and the possible tax of oil deposit the position.

4. using method according to claim 3, wherein in the step (b), determine that the factor of direct hydrocarbon detection factor threshold value comprises: background value, rock physics and the well-log information of each relative variation that the reflectance signature of exploration targets, single relative variation section and scatter diagram show.

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