CN1257412C - Method for determining underground speed structure for oil exploration - Google Patents

Abstract

The present invention relates to a method for determining underground velocity structure for oil exploration, which is a method for predicting the underground velocity structure and determining the burial position and the depth of a hydrocarbon reservoir. On the premise of using the seismic record generated by exciting every shot point and picked in every demodulator probe as the reference, the present invention comprises the orderly steps of scanning, processing data, picking up the velocity parameter of the reflected wave and fitting extrapolation output. The present invention can raise the velocity precision of a seismic wave and the velocity analysis efficiency, reduce the interference of human factors, overcome the limitation that the existing velocity analysis method is only suitable for the condition of the small rate of geophone offset and depth and achieve the purposes of point-by-point picking-up, high velocity, little manual intervention and high accuracy.

Description

A kind ofly be used for the method that velocity structure is descended in petroleum prospecting definitely

Technical field:

The invention belongs to the oil-gas exploration geophysics field in the field of earth sciences, relate in particular to a kind of method that velocity structure is descended in petroleum prospecting definitely that is used for.The present invention can predictably descend velocity structure, is to determine the embedding location of hydrocarbon-bearing pool and the system and method for the degree of depth.

Background technology:

Oil seismic exploration is by shot point (shot point) vibrations, by the technology of the underground close echo of acceptance point (geophone station) record.Seismic event is the The mean propagation velocity of seismic event at underground propagation apart from the ratio with the travel-time, and picking up seimic wave velocity is one of most crucial steps in the petroleum prospecting, and existing seimic wave velocity pick-up method efficient is not high, precision is low.

The common methods of being carried out velocity analysis by seismic data mainly contains following several:

A) speed spectrometry

The P212-229 page or leaf of " PRINCIPLE OF SEISMIC PROSPECTING WITH " that chief editor, petroleum industry publishing house publish is introduced the speed spectrometry by continental rise Meng.This method is visualized as horizontal layer with underground medium, then the multilayer HORIZONTAL LAYERED MEDIUM WITH HIGH ACCURACY is regarded as certain imaginary uniform dielectric, with hyp T-X curve relation replace actual non-double curve line the time draw root-mean-square velocity apart from equation.This short-cut method is only set up under the situation of geophone offset less (ratio of geophone offset and the degree of depth is less than 0.5), simultaneously, is also comprising many subjective factors and randomness in the manual interpretation of velocity spectrum, has reduced the precision of velocity analysis.If do highdensity velocity analysis work, the workload of manual interpretation velocity spectrum is huge.Speed spectrometry precision is not high, and efficient is low, and it is big manually to pick up workload, can not satisfy the requirement more and more higher to velocity accuracy.

B) tomographic inversion method.This method amount of calculation is huge, efficient is low, and inapplicable large batch of seismic data is handled.

This method at first designs an initial model, calculate by forward simulation, analyze the residual error of just drilling data and real data, revise initial velocity model, again more revised model just drill data and original earthquake data, the two person that substantially do not coincide is the final speed model of being asked.

C) the seismic migration method is used for velocity analysis.This method amount of calculation is huge, efficient is low.

Utilizing the result of pre-stack depth migration to revise the initial velocity model that is used to be offset, is a process that iterates.

The equation of time distance curve of reflection wave of horizontal multilayered medium is in the prior art

$t=2\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\frac{h_i}{v_i\sqrt{1-p^2{v_i}^2}}$

T is when walking, and n is the reflecting interface number, h _i, v _iBe respectively i layer thickness and interval velocity, p is a ray parameter.Work as pv _iLess, promptly the ray incident angle hour is omitted pv _iHigh-order term get $t={\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="C20031010343700131.png"\; state="\{\{state\}\}">t</figure-callout>}}_0+\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{t}_i{p}^2{v_i}^2,$ t ₀Be the self excitation and self receiving time.

Introduce the geophone offset parameter x, by omitting pv _iHigh-order term and cancellation p, can get $t^2={{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="C20031010343700131.png"\; state="\{\{state\}\}">t</figure-callout>}}_0}^2+\frac{x^2}{{v_r}^2}$

Wherein $V_r={\left[\frac{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{t}_i{v_i}^2}{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{t}_i}\right]}^{1/2}$ Be called root-mean-square velocity,

Root-mean-square velocity is under the situation of horizontal multilayered medium, with hyp T-X curve relation replace actual non-double curve line the time draw apart from equation.When seismic event is propagated in nonhomogeneous media, along different raypaths different velocity of propagation is arranged, seimic wave velocity be the function of seismic travel time be again the function of ray parameter p.With respect to the self excitation and self receiving ray velocity, along with the increasing of offset distance, ray average velocity increases.Theoretical analysis shows: when the ratio of offset distance and the zone of interest degree of depth was 1, maximum offset ray velocity and zero-offset ray velocity error reached 4%, and when offset distance continued to increase, error was bigger.Obtain accurate seimic wave velocity, the conventional speeds pick-up method is incompatible.

The objective of the invention is precision and velocity analysis efficient in order to improve seimic wave velocity, reduce the interference of human factor, overcome the smaller condition restriction that existing velocity analysis method only is suitable for the geophone offset and the degree of depth, reach pointwise pick up, fast, manual intervention is few, precision is high purpose.

In order to solve above technical matters, the present invention has used following technical scheme:

A kind ofly be used for the method that velocity structure is descended in petroleum prospecting definitely, described method is to be benchmark with the seismologic record by generation that each shot point is excited at each geophone station record, carries out descending definitely the method for velocity structure,

Concrete step is:

A sweep step: behind the input seismologic record, offset distance seismic data is among a small circle carried out linear sweep with Different Slope: promptly from 0 second to the seismologic record concluding time, in the concentrated 5-7 road earthquake data of respectively getting of shot point road collection and geophone station road, with the seismologic record sampling interval is that step-length is to lower slider, the scanning seismologic record, wherein sliding step be sampling interval 1-3 doubly;

The B data processing step: at time t place, the integral multiple that the time increment Δ s of shot point and geophone station phase neighboring trace, Δ g are taken as the seismologic record sampling interval respectively, the lineups slope changes from-n to+n, n=0.8 millisecond/rice wherein, increment is taken as 0.01 millisecond/meter; And with the summation of corresponding 5-7 road earthquake data, and comparing summed result, the slope of the maximal value correspondence of summing value is shot point ray parameter and ray parameter at receiver;

Sum formula wherein:

$\mathrm{ag}(m,t)=\underset{k=-n}{\overset{n}{\mathrm{\&Sigma;}}}S(i+k)(t+\mathrm{mk\&Delta;g})---\left(1\right)$

$\mathrm{as}(m,t)=\underset{k=-n}{\overset{n}{\mathrm{\&Sigma;}}}S(i+k)(t+\mathrm{mk\&Delta;s})---\left(2\right)$

C reflection wave speed parameter pick up step: after described scanning step and data processing step, utilize shot point ray parameter, ray parameter at receiver, hourage, sp location and geophone station location parameter to obtain the reflection wave speed parameter of each analyzing spot, wherein speed formula is:

$v=\sqrt{\frac{2\mathrm{ag}\&CenterDot;\mathrm{as}-r(v_{i_1}+v_{i_2})}{\mathrm{ag}+\mathrm{as}-2l/t}}---\left(3\right)$

D match extrapolation step: the reflection wave speed parameter to each analyzing spot of obtaining by step C carries out the outer push operation of match, carries out the speed match and obtains zero seimic wave velocity parameter partially;

Match in described method extrapolation step be for one reflection interval t, be the y coordinate figure with the per pass speed parameter, be the x coordinate figure with the position of per pass, carry out speed match push operation outward, the velocity amplitude when obtaining x=0; According to the size of match variance, select to use linear formula or more higher order polynomial carry out the speed match and obtain zero seimic wave velocity parameter partially;

E exports step: the process that is about to zero inclined to one side seimic wave velocity PARAMETER DRAFTING output.

The time increment at time t place's shot point and geophone station phase neighboring trace in the application of reality in described data processing step is taken as the integral multiple of seismologic record sampling interval: 1-2 doubly.

According to above technical scheme, the technique effect that the present invention can reach is:

The present invention descends the method for velocity structure definitely: it is the process that pointwise is picked up that surface seismic is intended zero inclined to one side seimic wave velocity pick-up method, and economy is rate, precision height rapidly and efficiently.Conventional ray method carries out two point ray tracing, need to follow the trail of many rays, just can find the ray of a travelling between specifying at 2, the present invention descends the method for velocity structure to utilize five parameters such as shot point ray parameter, ray parameter at receiver, whilst on tour, sp location, geophone station position definitely, only need to follow the trail of a ray, can pick up the reflection wave speed at the place of crest time on the different offset distances road, when this method is saved many machines than conventional ray tracing.Intend zero inclined to one side seismic velocity and the contrast of VSP speed and see Table 1, both errors are less as can be seen from the table.

Table 1 is intended zero inclined to one side seismic velocity and VSP speed contrast table

Layer position	T0(ms	VSP speed (m/s)	Intend zero speed (m/s) partially	Velocity error (%)
					T3 T4 T5	1802 2700 3220	2760 3325 3390	2709 3300 3371	1.8 0.8 0.5

Description of drawings:

Fig. 1 is for descending the process flow diagram of velocity structure method definitely in the petroleum prospecting

Fig. 2 is theoretical model figure

The velocity diagram of the road collection that Fig. 3 picks up for the VELOCITY EXTRACTION method

The real data velocity across that Fig. 4 picks up for the VELOCITY EXTRACTION method

Fig. 5 intends zero inclined to one side seimic wave velocity and VSP speed comparison diagram for the present invention picks up surface seismic

Embodiment:

Concrete grammar of the present invention is:

I. shot point ray parameter, ray parameter at receiver scanning are picked up:

Offset distance seismic data is among a small circle carried out linear sweep with Different Slope, pick up shot point ray parameter, ray parameter at receiver, hourage, sp location, geophone station location parameter.

Concrete steps are:

The input seismologic record, in the concentrated 5-7 road earthquake data of respectively getting of shot point road collection and geophone station road, from 0 second to the seismologic record concluding time, with seismologic record sampling interval (as 1 millisecond or 2 milliseconds) be step-length to lower slider, the scanning seismologic record is at t place sometime, the integral multiple that the time increment Δ s of shot point and geophone station phase neighboring trace, Δ g are taken as the seismologic record sampling interval respectively, the lineups slope changes from-n to+n, n=0.8ms/m, and increment is taken as 0.01ms/m.Then, with the 5-7 road earthquake data summation of correspondence, when the scanning summing value is maximum, output shot point ray parameter, ray parameter at receiver, hourage, sp location, geophone station location parameter, formula is formula (1), formula (2).

$\mathrm{ag}(m,t)=\underset{k=-n}{\overset{n}{\mathrm{\&Sigma;}}}S(i+k)(t+\mathrm{mk\&Delta;g})---\left(1\right)$

$\mathrm{as}(m,t)=\underset{k=-n}{\overset{n}{\mathrm{\&Sigma;}}}S(i+k)(t+\mathrm{mk\&Delta;s})---\left(2\right)$

$v=\sqrt{\frac{2\mathrm{ag}\&CenterDot;\mathrm{as}-r(v_{k_1}+v_{k_2})}{\mathrm{ag}+\mathrm{as}-2l/t}}---\left(3\right)$

Wherein l is an offset distance, be the distance of shot point to geophone station, t is a seismic travel time, v is for arriving the speed of geophone station ray again to reflection spot through shot point, S is a seismologic record, ag is a geophone station road collection scanning summing value, and as is a shot point road collection scanning summing value, and Δ s, Δ g are respectively the given shot point and the time increment of geophone station phase neighboring trace.

II. the zero-offset seimic wave velocity is picked up and treatment scheme

After obtaining shot point ray parameter, ray parameter at receiver, hourage, sp location, geophone station location parameter, utilize above-mentioned five parameters to obtain the reflection wave speed of each analyzing spot (formula (3)), because each analyzing spot all drops on per pass crest time place, therefore, also just obtained the reflection wave speed at per pass crest time place.In order to improve seimic wave velocity precision and velocity analysis efficient, reduce artificial interference, overcome the smaller condition restriction that existing velocity analysis method only is applicable to the geophone offset and the degree of depth, reach the purpose that pointwise is picked up, economy is quick, manual intervention is few, precision is high, adopt the method for low order fitting of a polynomial extrapolation to obtain the seimic wave velocity value of zero-offset to each road speed in the road collection, by the Xu Shiliang chief editor, in the P280-306 page or leaf of " algorithms most in use procedure set " that publishing house of Tsing-Hua University publishes the match Extrapolation method is introduced.

Step is: for a certain reflection interval of t, being the y coordinate figure with the per pass speed parameter, is the x coordinate figure with the position of per pass, the velocity amplitude of (just offset distance is zero) when carrying out speed match extrapolation and obtaining x=0.According to the size of match variance, select to use linear formula or more higher order polynomial carry out the speed match and obtain zero seimic wave velocity value partially.

Be to use method of the present invention at concrete geological data to operate and analytic process below.

(1) theoretical model of velocity acquiring method calculates

Mathematical model parameter is: mesh-density DX=10 rice, DY=10 rice, node is counted NX=2500, NY=501.Recording geometry is: 50 meters of track pitches, and 100 meters of shot intervals, 120 roads/big gun, record length 4 seconds, 1 millisecond of sampling interval is gathered 170 big guns altogether.Be recorded as the input data just to drill shot point, by velocity pick, the interval velocity model and the realistic model that obtain match.Fig. 2 is a theoretical model, and Fig. 3 is the velocity diagram based on a road collection of invention technology acquisition.

(2) real data of velocity acquiring method is handled

With said method actual seismic data is handled.Acquisition parameter: 96 trace records, 24 stacks, 25 meters of track pitches, 50 meters of shot intervals, 250 meters of smallest offset distances, 2625 meters of maximum offsets, record length 6 seconds, 2 milliseconds of sampling interval.Root-mean-square velocity and interval velocity section figure that Fig. 4 picks up for the inventive method.

(3) the speed precision analysis of obtaining

Consider the accuracy of VSP speed quality and precision, carried out the comparative analysis work of invention technical speed acquisition methods and VSP speed.Fig. 5 is two kinds of speed correlation curves, the curvilinear characteristic basically identical of two kinds of speed among the figure, and the speed of descending the method for velocity structure to obtain definitely has higher precision.Intend zero inclined to one side seismic velocity and the contrast of VSP speed and see Table 1, both errors are less as can be seen from the table.

Claims (2)

1. one kind is used for the method that velocity structure is descended in petroleum prospecting definitely, and described method is to be benchmark with the seismologic record by generation that each shot point is excited at each geophone station record, carries out descending definitely the method for velocity structure, it is characterized in that:

A scanning step: behind the input seismologic record, offset distance seismic data is among a small circle carried out linear sweep with Different Slope: promptly from 0 second to the seismologic record concluding time, in the concentrated 5-7 road earthquake data of respectively getting of shot point road collection and geophone station road, with the seismologic record sampling interval is that step-length is to lower slider, the scanning seismologic record, wherein sliding step be sampling interval 1-3 doubly;

The B data processing step: at time t place, the integral multiple that the time increment Δ s of shot point and geophone station phase neighboring trace, Δ g are taken as the seismologic record sampling interval respectively, the lineups slope changes from-n to+n, n=0.8 millisecond/rice wherein, increment is taken as 0.01 millisecond/meter; And with the summation of corresponding 5-7 road earthquake data, and comparing summed result, the slope of the maximal value correspondence of summing value is shot point ray parameter and ray parameter at receiver;

Sum formula wherein:

$\mathrm{ag}(m,t)=\underset{k=-n}{\overset{n}{\mathrm{\&Sigma;}}}S(i+k)(t+\mathrm{mk\&Delta;g})---\left(1\right)$

$\mathrm{as}(m,t)=\underset{k=-n}{\overset{n}{\mathrm{\&Sigma;}}}S(i+k)(t+\mathrm{mk\&Delta;s})---\left(2\right)$

C reflection wave speed parameter pick up step: after described scanning step and data processing step, utilize shot point ray parameter, ray parameter at receiver, hourage, sp location and geophone station location parameter to obtain the reflection wave speed parameter of each analyzing spot, wherein speed formula is:

$v=\sqrt{\frac{2\mathrm{ag}\&CenterDot;\mathrm{as}-r(v_{t_1}+v_{t_2})}{\mathrm{ag}+\mathrm{as}-2I/t}}---\left(3\right)$

D match extrapolation step: the reflection wave speed parameter to each analyzing spot of obtaining by step C carries out the outer push operation of match, carries out the speed match and obtains zero seimic wave velocity parameter partially;

Match in described method extrapolation step be for one reflection interval t, be the y coordinate figure with the per pass speed parameter, be the x coordinate figure with the position of per pass, carry out speed match push operation outward, the velocity amplitude when obtaining x=0; According to the size of match variance, select to use linear formula or more higher order polynomial carry out the speed match and obtain zero seimic wave velocity parameter partially;

E exports step: the process that is about to zero inclined to one side seimic wave velocity PARAMETER DRAFTING output.

2. a kind of method that velocity structure is descended in petroleum prospecting definitely that is used for as claimed in claim 1 is characterized in that: the integral multiple that the time increment at time t place's shot point and geophone station phase neighboring trace in described data processing step is taken as the seismologic record sampling interval is 1-2 times.

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