CN100349006C - Method for determining distribution of lithologic character and liquid by using inversion technique of wave impedance - Google Patents

Abstract

The present invention relates to a method for determining distribution of lithologic characters and liquids by using the wave impedance inversion technique, which is used in the technical field for physical exploration for petroleum. An AI curve and An EI curve are obtained, a seismic incoming angle which can obviously differentiate different lithologic characters is selected, and an AI-EI cross plot is plotted by a well log; data is superposed according to the seismic angle path extracted from the incoming angle; the EI inversion of the over well survey line is carried out according to the extractive seismic angle path superposition data; the AI inversion of the over well survey line is carried out by utilizing the full superposition data; the orthogonal lithologic character and the fluid projection line which are explained by the AI-EI cross plot are utilized as the basis for determining the distribution of the lithologic character and the liquid. The distribution of the lithologic character and the liquid relatively tallies with the actual work area.

Description

A kind of method of determining lithology and fluid distribution with wave impedance inversion technique

Technical field

The present invention relates to oil physical prospecting technical field, belong to seismic data inverting category, specifically is a kind of method of determining lithology and fluid distribution with wave impedance inversion technique.

Background technology

The process of seismic prospecting, be exactly on the series of points on the ground, utilize artificial excitation's seismic event, seismic event is to underground propagation, when running into wave impedance interface (wave impedance unequal face in stratum promptly), seismic event produces reflex on the wave impedance interface, the seismic wave propagation direction changes, and seismic event begins upwards to propagate, and is settling receiver on a series of acceptance points on the ground, receive the seismic event of upwards propagating, this is the positive process (ground observation process) of seismic prospecting.Wave impedance is exactly the function of seismic wave propagation speed and density of earth formations, and its size has reflected the distribution situation of oil gas in the structure of subsurface formations and structure and the reservoir, is crucial parameter in oil-gas exploration, exploitation, the recovery process.Wave impedance inversion is exactly the reflected signal at the reflection subsurface formations interface that receives according to ground, asks for the process of subsurface formations wave impedance, belongs to anti-process.

Wave impedance inversion starts from the seventies, is often referred to a kind of technical method that utilizes the poststack seismic data to carry out inverting, is to carry out reservoir characteristic to describe, carry out one of important means of reservoir study in the two and three dimensions space.It combines seismic data, well-log information, geologic interpretation, making full use of well-log information has higher vertical resolution and seismic section and has and walk crosswise successional characteristics preferably, " convert " seismic section to wave impedance section, not only be convenient to the explanation personnel seismic data is connected contrast with well-log information, and can effectively study the stratum variations of physical parameters, become an indispensable explanatory treatment technology in the interpretation technique.

Sound impedance (AI) is the deposition of primary seismic wave speed and density of earth formations, and the basic assumption of AI inverting is that the seismic amplitude after the stack is directly proportional with the reflection coefficient of normal incidence, and has ignored the information that amplitude changes with geophone offset.The AI inverting is a kind of common technology of lithology prediction, but in certain areas, and it is more serious to utilize sound impedance to carry out the lithological inversion multi-solution.In this case, just be necessary to introduce the inversion method that has shear wave velocity information.

Elastic wave impedance (EI) inverting is a kind of conventional sound impedance inverting and indication using prestack seismic amplitude change (AVO) inverting with geophone offset seismic inversion technology that combines, its advantage is to have considered that the seismic reflection amplitude along with incident angle changes, can calculate the wave impedance under the different incidence angles situation.Because EI combines convection cell and the relatively more responsive shear wave information of lithological change, so utilize it to determine that lithology and fluid space spread are present popular methods.

But at some complex area, when incident angle 40 the degree or more can distinguish different lithology fully with EI more than the high angle, and the seismic data of high angle often is to be difficult to obtain in the actual acquisition process like this, at this moment utilizes simple EI inverting can not obtain gratifying result equally.

Summary of the invention

The object of the present invention is to provide a kind of utilize AI and in, determine the method that lithology and fluid distribute with wave impedance inversion technique when in the low angle EI environment earthquake Data Processing being determined the lithology poor effect.

Lithology provided by the invention and fluid Forecasting Methodology, the specific implementation step comprises:

(1) formula is obtained AI curve and EI curve below densimetric curve, compressional wave curve and the utilization of shear wave curve of known well logging.

The AI computing formula is as follows:

AI＝ρV

AI＝ρV

The EI computing method are as follows:

$\mathrm{EI}\left(\mathrm{\β}\right)=V_{p0}{\mathrm{\ρ}}_0\left[{\left(\frac{V_p}{V_{p}0}\right)}^{{\cos }^p\mathrm{\β}+{\sin }^p\mathrm{\β}}{\left(\frac{V_s}{V_{s0}}\right)}^{-8K{\sin }^p\mathrm{\β}}{\left(\frac{\mathrm{\ρ}}{{\mathrm{\ρ}}_0}\right)}^{{\cos }^p\mathrm{\β}-4K{\sin }^p\mathrm{\β}}\right]$

In the formula, V _pBe velocity of longitudinal wave, V _sFor shear wave velocity, ρ are density, $K=V_s^2/V_p^2$ Be constant, be taken as the mean value of adjacent layer.V _P0, V _S0And ρ ₀Be three with reference to constant, purpose is in order to make EI value under the different angles ask for and AI value under same yardstick.β is an independent variable, and the pass between the incident angle θ is tan ^pβ=sin ²θ, norm p are one the p value can dynamically be adjusted, and when the longitudinal and transverse wave velocity difference of two layer medium increases and decreases in the same way, can suitably amplify p greater than zero real number that reverse situation is next can to make decimal of p convergence.

(2) by the AI-EI X plot under the logging trace drafting different incidence angles situation, select an earthquake incident angle (different lithology can well make a distinction under this angle), according to the earthquake angle trace-stacking data of this angle incident angle extraction.Be different from conventional full superposition of data, trace-stacking data in earthquake angle all do not stack up the data that come from all reflection angles, and just the stacked data in the selected reflection angle scope are added up, and such superposition of data and angle have much relations.

(3) carried out the EI inverting of well surveying line according to the earthquake angle trace-stacking data of extracting.

(4) utilize full superposition of data to carry out the AI inverting of well surveying line.

(5) in conjunction with other useful well logging information, geological information etc., explain mutually orthogonal lithology projection line and fluid projection line at the AI-EI of logging trace X plot, determine the distributing position of distribution of sandstone position and different fluid according to them, and this explanation results is projected on the superimposition section of AI and EI, determine different lithology and the fluid space distribution on the section of crossing the well surveying line.

The specific implementation principle of lithology of the present invention and fluid prediction is as follows:

Densimetric curve, compressional wave curve and shear wave curve by fixed well are obtained EI curve and AI curve, draw AI and EI X plot under the different incidence angles degree, under the less situation of incident angle, in the time of all can not distinguishing different lithology preferably with AI and EI, on X plot, explaining mutually orthogonal lithology projection line and fluid projection line according to fixed well information, on the lithology projection line, different lithology can obtain maximum differentiation, on the fluid projection line, dissimilar fluids can obtain maximum differentiation.

Select a suitable earthquake incident angle according to lithology projection line and fluid projection line, earthquake angle superposition of data to this angle carries out the elastic wave impedance inverting, and the conventional stacking data carried out the sound impedance inverting, obtained after above two kinds of impedance bodies, with the AI-EI X plot that explained lithology projection line and fluid projection line as guidance, the different lithology zone and the fluid mass that explain on the X plot are projected to respectively on the superimposed section of EI and AI, just can determine lithology and fluid distribution.

The present invention utilizes the lithology of the quadrature that explains on the AI-EI X plot and the conduct of fluid projection line to determine the foundation that lithology and fluid distribute, the lithology of determining, fluid distribution and actual work area are more identical, most of gas sand is positioned on the water bearing sand simultaneously, and this also meets geologic rule.

Description of drawings

Fig. 1 (a) is that 0 degree is to the 90 AI-EI X plot synoptic diagram of spending under the incident angles;

Fig. 1 (b) is the AI-EI X plot of incident angle 25 degree of the present invention;

In Fig. 1, on behalf of mud stone, blueness, white be clean sandstone, green for oozing sandstone; Redness is that gas-bearing formation, yellow are air water layer together.Sky blue lines are the lithology projection line, and the pink colour lines are the fluid projection line, and have demonstrated lithology projection line and fluid projection line on X plot, determine lithology and fluid distribution situation thus.

Fig. 2 (a) was the inversion result figure of well profile sound impedance.

Fig. 2 (b) is 25 EI inversion result figure when spending for incident angle;

The lithology distributions location drawing of crossing the well surveying line that Fig. 3 determines for the present invention;

Fig. 3 is upper left to be AI-EI25 ° of X plot, and the delineation district is sandstone; Colour code is gamma (GAPI) value, wherein, and sandstone: GAPI＜100, mud stone: GAPI＞100; Fig. 3 below is an EI25 ° of inverting section, the delineation district of the corresponding the picture left above of black region among the figure.

The gas sand of crossing the well surveying line that Fig. 4 determines for the present invention and the distribution situation figure of water bearing sand;

Wherein: upper left red curve enclosing region is the gas sand distributing position, the red area of corresponding figure below;

The red curve enclosing region of top right plot is an air water sandstone distributing position, the yellow area of corresponding figure below.

Fig. 4 as seen, most of gas sand is positioned on the water bearing sand.

Fig. 5 (a) is test data AI of the present invention and EI curve;

Fig. 5 (b) is the conventional stacking section.

Fig. 5 (c) is 25 degree angle trace-stacking sections.

Embodiment

Densimetric curve, compressional wave curve and shear wave curve by fixed well are obtained EI and AI curve, analyze AI and the EI X plot drawn under the different incidence angles degree.Can do not obtained according to compressional wave (Vp) curve by the Gardner formula when having densimetric curve, this formulate is as follows:

$\mathrm{\ρ}=a{V}_p^b$

Wherein, a, b are constants.

When not having shear wave (Vs) curve, can obtain by following Castagna formula:

V _p＝1.16V _s+1.36

When utilize separately AI or in, when low angle EI can not separate different lithology, on the AI-EI of logging trace X plot, explain mutually orthogonal lithology projection line and fluid projection line.Select an earthquake incident angle θ simultaneously, so that ask for the earthquake angle trace-stacking data under this angle, this incident angle can not be too big, generally below 25～35 degree, because the geological data of high angle is difficult to collect in actual acquisition.

Choosing with θ is an angular range of central angle, according to prestack CMP road collection behind the moving school of crossing well, asks for earthquake angle trace-stacking data, and this angular range generally is advisable with 5～10 degree.Use conventional Inversion Software then these data are carried out the elastic wave impedance inverting, use the conventional stacking data wave impedance inversion of making a sound simultaneously.

After having obtained above two kinds of impedance bodies, lithology projection line that explains on the AI-EI X plot according to logging trace and fluid projection line, on X plot, determine the band of position of different lithology and fluid, again they are projected to respectively on the superimposed section of EI and AI, thereby determine lithology and the space distribution of fluid on the whole piece survey line.

Shown in Figure 5 is test data.

(a) be AI and EI curve, wherein redness is the AI curve, and Dark grey is the EI curve.

(b) be the conventional stacking section.

(c) be 25 degree angle trace-stacking sections.

Earlier make X plot according to AI and EI curve, using dual-projection line selection on the X plot then, to have got incident angle be that the angle trace-stacking sections of 25 degree carry out the EI inverting, at last with the AI-EI X plots of 25 degree as guidance, use in conjunction AI, EI inversion result have been determined lithology and fluid distribution position.

Claims (4)

1, a kind ofly determine the method that lithology and fluid distribute, gather the physical prospecting data, obtain densimetric curve, compressional wave curve and the shear wave curve of known well logging by analysis, it is characterized in that adopting following steps to realize by conventional means with wave impedance inversion technique:

(1) formula draws sound impedance AI curve and elastic wave impedance EI curve below utilizing;

AI＝ρV

$\mathrm{EI}\left(\mathrm{\β}\right)=V_{p0}{\mathrm{\ρ}}_0\left[\begin{array}{ccc}{\left(\frac{V_p}{V_{p0}}\right)}^{{\cos }^p\mathrm{\β}+{\sin }^p\mathrm{\β}}& {\left(\frac{V_s}{V_{s0}}\right)}^{-8K{\sin }^p\mathrm{\β}}& {\left(\frac{\mathrm{\ρ}}{{\mathrm{\ρ}}_0}\right)}^{{\cos }^p\mathrm{\β}-4K{\sin }^p\mathrm{\β}}\end{array}\right]$

In the formula, V _pBe velocity of longitudinal wave, V _sFor shear wave velocity, ρ are density, $K=V_s^2/V_p^2$ Be constant, be taken as the mean value of adjacent layer, V _P0, V _S0And ρ ₀β is an independent variable with reference to constant to be three, and the pass between the incident angle θ is tan ^pβ=sin ²θ, norm p be one greater than zero real number;

(2) the earthquake incident angle of different lithology can be obviously distinguished in selection, draws the AI-EI X plot by logging trace; Earthquake angle trace-stacking data according to this angle incident angle extraction;

When utilize separately AI or in, when low angle EI can not separate different lithology, on the AI-EI of logging trace X plot, explain mutually orthogonal lithology projection line and fluid projection line, selecting earthquake incident angle θ is the 30-35 degree, and choosing with θ is that an angular range of central angle is the 5-10 degree;

(3) carried out the EI inverting of well surveying line according to the earthquake angle trace-stacking data of extracting;

(4) utilize full superposition of data to carry out the AI inverting of well surveying line;

(5) according to known well logging, geologic information, draw mutually orthogonal lithology projection line and fluid projection line at the AI-EI X plot, and the lithology on X plot zone and fluid mass projected to respectively on the superimposed section of EI and AI, determine lithology and the fluid distributing position on the whole piece survey line.

2, a kind of method of determining lithology and fluid distribution with wave impedance inversion technique according to claim 1, it is characterized in that: norm p value is dynamically adjusted, when the longitudinal and transverse wave velocity difference of two layer medium increases and decreases in the same way, amplify p, the next decimal of p convergence that makes of reverse situation.

3, according to claim 1ly a kind ofly determine the method that lithology and fluid distribute, it is characterized in that: when having densimetric curve, do not obtain according to compressional wave Vp curve with following formula with wave impedance inversion technique:

ρ＝aV _p ^b

Wherein, a, b are constants.

4, according to claim 1ly a kind ofly determine the method that lithology and fluid distribute, it is characterized in that: when not having shear wave Vs curve, obtain by following formula with wave impedance inversion technique:

V _p＝1.16V _s+1.36

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