CN100349016C - Method for scanning radiation two-dimensional acoustic field in formations generated from a borehole - Google Patents

Abstract

The present invention relates to a method for scanning and irradiating a two-dimensional sound field in stratum which is positioned at the side of a well by reflecting sound wave imaging logging or well-to-well sound wave exploration. Each array element of an underground phased array sound wave radiator is respectively excited, the delay time (the transmitting phase shift) of excitation signals of each array element is adjusted, synthesis main beams radiated by the phased linear array sound wave radiator are deflected, the delay time of the excitation signals of every two adjacent array elements of the underground phased array sound wave radiator is continuously and orderly increased or decreased, the vertical directivity of sound beams generated by the radiator is changed, and the scan and the irradiation of the sound field in a stratum which is positioned out of the well are realized. The present invention can scan the stratum which is positioned at the side of the well by using sound waves, and can realize the limitation of the sound beam radiation angular width and an incident angle and the accurate control of the propagation direction of sound waves. Thereby, the directional scan of the sound waves and the irradiation of the sound field are realized, the resolution of the exploration is improved, and the detection range is enlarged.

Description

The method of scanning radiation two-dimensional acoustic field in near-borehole formation

Technical field

Patent of the present invention belongs to the applied geophysics acoustic logging, relates between a kind of borehole acoustic reflection imaging or well in the sonic prospecting method of scanning radiation two-dimensional acoustic field in the other stratum of well.

Technical background

The technology of the acoustic logging instrument that uses in the in-site measurement is mainly used in the measurement and the exploration on individual well or local stratum, along with the development of technology at present can be to the extraradial sound field of well, and then acoustic measurement is carried out on the other stratum of well.

Chinese patent ZL 01268574.7 discloses a kind of down-hole array transducer, form along same axis arrangement by a plurality of above pipe shape transducers (array element), have a channel rubber to isolate to realize the acoustic-electric between the adjacent array element between each transducer (array element), each array element can be that piezoelectricity pipe or other are similar to the transducer of point sound source.Attempt to utilize this down-hole array transducer to excite phase control, realize the deflection of the synthetic main beam of adjustment radiator radiation, the spatial direction of control, acoustic measurement is carried out on the other stratum of realization well.

In in sonic prospecting engineerings such as borehole acoustic reflection imaging and crosshole seismic exploration, all relating to by well in near-borehole formation the problem of radiated sound field, the directivity of radiative acoustic wave and the control of beam width are the topmost performances of sound radiator.Especially under the situation of stratigraphic structure more complicated, only single guide sound wave radiation direction can't be carried out the high resolving power measurement to near-borehole formation, and its result also has multi-solution, influences the reliability and the degree of accuracy of reservoir exploration.

Current other stratum acoustic sounding need solve the raising investigation depth, increase investigative range for well, comprises the accurate control of the restriction harmony direction of wave travel of radiation acoustic beam angular width, incident angle, thereby realizes the directional scanning radiated sound field of sound wave.

Summary of the invention

The object of the invention is to provide the higher investigation depth of a kind of realization, increases investigative range, the method for scanning radiation sound field in borehole axis symmetry stratum of strict control radiation acoustic beam angular width, incident angle.

The present invention realizes in the following way:

The method of scanning radiation two-dimensional acoustic field in near-borehole formation, with desired depth in the underground phased array sound radiator lower going-into-well, each array element is wherein excited respectively, adjust the time delay (emission phase shift) of the pumping signal of each array element simultaneously, make and it is characterized in that the synthetic main beam deflection of phased linear array sound radiator radiation:

The yawing moment of control radiative acoustic wave is determined by following formula: $\mathrm{\τ}=\frac{d\sin {\mathrm{\θ}}_s}{c}---\left(1\right),$

Wherein, d is the distance between the adjacent array element, and c is the longitudinal wave velocity of sound source place medium, and τ is the time delay of pumping signal that adjacent array element adds, θ _sDeflection angle for phased radiator Main beam main lobe.

Constantly increase or reduce the time delay of the adjacent array element pumping signal of each underground phased array sound radiator successively, change the vertical directivity of the acoustic beam of radiator generation, realize all directions scanning radiation sound field in the stratum of well vertical direction.

The present invention also realizes in the following way:

The incident angle θ of Main beam main lobe _iShould be less than first critical angle.It is generally acknowledged that the longitudinal wave velocity of mud is 1600m/s in the well, the longitudinal wave velocity scope on stratum is 1800m/s ~ 7000m/s, so the scope of the first critical angle on various stratum is 13 ° ~ 63 °.When the deflection angle of phased linear array sound radiator radiation acoustic beam when zero is increased to first critical angle, the deflection angle that enters the sonic propagation direction on stratum can change to 90 ° from-90 °.

The overall diameter scope of transducer array is 60mm-95mm, and operating frequency range is 5kHz-25kHz.

For the phased linear array that is made of a plurality of point sources, the deflection angle of its radiator Main beam and acoustic beam angular width are calculated by following functional expression: $D_1(\mathrm{\θ},{\mathrm{\θ}}_s,\mathrm{\ω})=\frac{\left|\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{A}_i{e}^{-\mathrm{jk}\left[(\sin \mathrm{\θ}-\sin {\mathrm{\θ}}_s)(i-1)d\right]}\right|}{\left|\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{A}_i\right|}---\left(2\right)$

I represents array element sequence number, A in the formula _iBeing the Oscillation Amplitude of i array element, also is the amplitude weighting factor.Amplitude weighting is used to solve the control of beamwidth and side lobe levels, and the amplitude of each array element is by dull decline of center symmetry of battle array, and the main beam of phased linear array broadens, and side lobe levels reduces.

For the phased linear array that is made of a plurality of pipes, the deflection angle of its radiator Main beam and acoustic beam angular width are calculated by following formula: D=D ₁* D ₂(3), wherein,

$D_2\left(\mathrm{\&theta;}\right)={\left[\frac{{\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="C20051005889100101.png"\; state="\{\{state\}\}">J</figure-callout>}}_0^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\cos \mathrm{\&theta;}\right)+{\cos }^2\mathrm{\&theta;}{J}_1^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\cos \mathrm{\&theta;}\right)}{{\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="C20051005889100101.png"\; state="\{\{state\}\}">J</figure-callout>}}_0^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\right)+J_1^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\right)}\right]}^{\frac{1}{2}}\&times;\frac{\sin \left(\frac{\mathrm{\&pi;h}}{\mathrm{\&lambda;}}\sin \mathrm{\&theta;}\right)}{\frac{\mathrm{\&pi;h}}{\mathrm{\&lambda;}}\sin \mathrm{\&theta;}}---\left(4\right)$

D ₂Be the directivity function of pipe shape sound radiator, a and h are respectively the mean radius and the height of pipe transducer, and λ is a wave length of sound.

The present invention can carry out sound wave scanning to the other stratum of well, can realize the accurate control of the restriction harmony direction of wave travel of radiation acoustic beam angular width, incident angle, thereby realize the directional scanning radiated sound field of sound wave, has improved exploration resolution, has increased investigative range.

Description of drawings

When being incident in the borehole wall, the compressional wave sound wave that accompanying drawing 1 produces for sound source in the well in near-borehole formation, produces the refracted longitudinal wave synoptic diagram;

Accompanying drawing 2 can the deflection of radiation angle be the rotational symmetry sound field synoptic diagram of θ for the phased linear array that constitutes at a distance of a plurality of array elements for d;

Accompanying drawing 3 is the directivity function of the phased linear array sound radiator of many pipes array element composition, three deflection angles that curve is corresponding different.

Embodiment

Describe technical characterstic of the present invention in detail below in conjunction with drawings and Examples.

Sound field involved in the present invention has axial symmetry with respect to by the well logging vertical scan direction, can be described as two-dimensional acoustic field.

Usually, have only when the sound wave in the well and just can make sound wave enter the stratum when being incident in the borehole wall less than first critical angle.Therefore the radiation acoustic beam that will control the underground phased array sound radiator makes acoustic wave energy as much as possible enter the stratum to be incident in borehole wall interface less than first critical angle, thereby improves the investigation depth of acoustic measurement and the signal to noise ratio (S/N ratio) of received signal.

The present invention can control and adjust the deflection angle of phased linear array radiation acoustic beam by control and the method for adjusting the time delay of the adjacent array element pumping signal of phased linear array, makes it all the time less than first critical angle.For directional scanning radiative acoustic wave in the stratum, the angular width of radiation acoustic beam should be as much as possible little, thereby make acoustic measurement that higher spatial resolution be arranged.The present invention can make the acoustic beam angular width of phased linear array radiation less by selecting phased linear array element number of array and array element distance and carrying out methods such as pumping signal amplitude weighting.As, the radiation acoustic beam angular width of the phased linear array that constitutes at a distance of 14 point sound source array elements for 6cm reaches 7 °.

The present invention constantly adjusts the time delay of the adjacent array element pumping signal of underground phased array sound radiator, to change the direction of propagation of the acoustic beam that radiator produces, make sound wave be not more than in the scope of first critical angle increasing or decreasing successively in the incident angle of the borehole wall, just can realize scanning radiation sound field in the stratum of different directions outside well.The deflection angle of radiation acoustic beam is when zero is increased to first critical angle, and the deflection angle that enters the sonic propagation direction on stratum just changes to 90 ° from-90 °.Because the scanning radiation measurement of each depth point needs the regular hour, therefore, the present invention is suitable for the measurement of down-hole acoustic wave apparatus different depth point in well, i.e. " point is surveyed ".Also can realize the continuous sweep acoustic measurement is carried out on the stratum of different depth in the less demanding occasion that tests the speed.

The underground phased array sound radiator that the present invention uses, it is a kind of array transducer, form along same axis arrangement by 3 above pipe shape transducers (array element), have a channel rubber to isolate between each transducer (array element) to realize the acoustic-electric between the adjacent array element.Each array element can be the piezoelectricity pipe, also can be other transducer that is similar to point sound source.

The present invention carries out the accurate phase control that excites to each array element wherein, thereby the emission phase shift that can adjust each array element obtains the deflection of the synthetic main beam of phased linear array sound radiator radiation, makes it have directive property and the radiation main lobe width that can control.

Fig. 1 of the present invention is the synoptic diagram of incident angle less than first critical angle.

Suppose that the longitudinal wave velocity in interior liquid of well and the near-borehole formation is respectively V _fAnd V _pFor general stratum, V is always arranged _f＜V _pThe sound wave that sound source produces in well is with incident angle θ _iWhen being incident in the borehole wall, has only the θ of satisfying _i＜θ _cShi Caineng produces refracted longitudinal wave in the other stratum of well, wherein ${\mathrm{\&theta;}}_c=\arcsin \left(\frac{V_f}{V_p}\right)$ Be first critical angle.It is generally acknowledged the longitudinal wave velocity V of mud in the well _fBe 1600m/s, the longitudinal wave velocity V on stratum _pScope be 1800m/s-7000m/s, so, the first critical angle θ on various stratum _cScope be 13 °-63 °.

Fig. 2 of the present invention for phased linear array by the definite synoptic diagram of deflection angle, by the yawing moment that can control its radiative acoustic wave time delay of controlling adjacent array element pumping signal at a distance of the Main beam of the phased linear array radiation that constitutes for a plurality of array elements of d.When using phased linear array in well, the deflection angle of phased linear array just is exactly the incident angle that sound wave is incident in borehole wall interface in the well.Therefore as long as the radiation acoustic beam of control underground phased array sound radiator is to be incident in the interface of liquid and borehole wall stratum in the well less than first critical angle, just can make acoustic wave energy as much as possible enter the stratum, thereby fundamentally improve the investigation depth of acoustic measurement and the signal to noise ratio (S/N ratio) of received signal.The deflection angle of the Main beam of phased linear array radiation is definite by formula (1),

$\mathrm{\&tau;}=\frac{d\sin {\mathrm{\&theta;}}_s}{c}---\left(1\right),$

Wherein, d is the distance between the adjacent array element of phased linear array, and c is the longitudinal wave velocity of sound source place medium, and τ is the time delay of pumping signal that adjacent array element adds, θ _sDeflection angle for phased radiator Main beam main lobe.

The deflection angle of its radiator Main beam and acoustic beam angular width are calculated by formula (2).

$D_1(\mathrm{\&theta;},{\mathrm{\&theta;}}_s,\mathrm{\&omega;})=\frac{\left|\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{A}_i{e}^{-\mathrm{jk}\left[(\sin \mathrm{\&theta;}-\sin {\mathrm{\&theta;}}_s)(i-1)d\right]}\right|}{\left|\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{A}_i\right|}---\left(2\right),$

Meaning in the formula (2) as shown in Figure 2, i represents array element sequence number, A _iBeing the Oscillation Amplitude of i array element, also is the amplitude weighting factor.In general, amplitude weighting is used to solve the control of beamwidth and side lobe levels.If the amplitude of each array element is by dull decline of center symmetry of battle array, then the main beam of phased linear array broadens, and side lobe levels reduces.

For the phased linear array that is made of a plurality of pipes, the deflection angle of its radiator Main beam and acoustic beam angular width are calculated by formula (3).D=D ₁* D ₂(3), wherein:

$D_2\left(\mathrm{\&theta;}\right)={\left[\frac{{\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="C20051005889100101.png"\; state="\{\{state\}\}">J</figure-callout>}}_0^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\cos \mathrm{\&theta;}\right)+{\cos }^2\mathrm{\&theta;}{J}_1^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\cos \mathrm{\&theta;}\right)}{{\mathrm{<figure-callout\; id="0"\; label="J"\; filenames="C20051005889100101.png"\; state="\{\{state\}\}">J</figure-callout>}}_0^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\right)+J_1^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\right)}\right]}^{\frac{1}{2}}\&times;\frac{\sin \left(\frac{\mathrm{\&pi;h}}{\mathrm{\&lambda;}}\sin \mathrm{\&theta;}\right)}{\frac{\mathrm{\&pi;h}}{\mathrm{\&lambda;}}\sin \mathrm{\&theta;}}---\left(4\right)$

In the formula, D ₂Be the directivity function of pipe shape sound radiator, a and h are respectively the mean radius and the height of pipe transducer, and λ is a wave length of sound.Can control and adjust the deflection angle of phased linear array radiation acoustic beam by control and the method for adjusting the time delay of the adjacent array element pumping signal of phased linear array, make it all the time less than first critical angle.

For directional scanning radiative acoustic wave in the stratum, the angular width of underground phased array sound radiator radiation acoustic beam should be as much as possible little, guaranteeing can to keep less angular width after this acoustic beam penetrates the stratum, thereby makes acoustic measurement that higher spatial resolution be arranged.According to formula (2-3), can make the acoustic beam angular width of phased linear array radiation less by selecting phased linear array element number of array and array element distance and carrying out methods such as amplitude weighting.As shown in Figure 3, the radiation acoustic beam angular width of the phased linear array that constitutes at a distance of 14 point sound source array elements for 6cm reaches 7 °.

Constantly increase or reduce the time delay of the adjacent array element pumping signal of underground phased array sound radiator successively, change the direction of propagation of the acoustic beam of radiator generation, make sound wave be not more than in the scope of first critical angle increasing or decreasing successively in the incident angle of the borehole wall, just can realize scanning radiation sound field in the stratum of different directions outside well.As depicted in figs. 1 and 2, when the deflection angle of phased linear array sound radiator radiation acoustic beam when zero is increased to first critical angle, the deflection angle that enters the sonic propagation direction on stratum can change to 90 ° from-90 °.Because the scanning radiation measurement of each depth point needs the regular hour, therefore, the inventive method generally is suitable for the measurement of down-hole acoustic wave apparatus different depth point in well, i.e. " point is surveyed ".Less demanding occasion also can realize the continuous sweep acoustic measurement is carried out on the stratum of different depth with said method testing the speed.

Claims (4)

1, a kind of in near-borehole formation the method for scanning radiation two-dimensional acoustic field, with desired depth in the underground phased array sound radiator lower going-into-well, each array element is wherein excited respectively, adjust the time delay of the pumping signal of each array element simultaneously, make and it is characterized in that the synthetic main beam deflection of phased linear array sound radiator radiation:

Have the yawing moment of control radiative acoustic wave to determine by following formula: $\mathrm{\&tau;}=\frac{d\sin {\mathrm{\&theta;}}_s}{c}---\left(1\right),$

Wherein, d is the distance between the adjacent array element, and c is the longitudinal wave velocity of sound source place medium, and τ is the time delay of pumping signal that adjacent array element adds, θ _sBe the deflection angle of phased radiator Main beam main lobe,

Constantly increase or reduce the time delay of the adjacent array element pumping signal of each underground phased array sound radiator successively, change the vertical directivity of the acoustic beam of radiator generation, realize scanning radiation sound field in near-borehole formation;

The incident angle θ of Main beam main lobe _sScope be to be not more than sound wave by the first critical angle that is incident in borehole wall interface in the well;

For the phased linear array that is made of a plurality of point sources, the deflection angle of its radiator Main beam and acoustic beam angular width are calculated by following functional expression: $D_1(\mathrm{\&theta;},{\mathrm{\&theta;}}_s,\mathrm{\&omega;})=\frac{\left|\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{A}_i{e}^{-\mathrm{jk}[(\sin \mathrm{\&theta;}-{\sin \mathrm{\&theta;}}_s)(i-1)d}\right|}{\left|\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{A}_i\right|}---\left(2\right)$

I represents array element sequence number, A in the formula _iBeing the Oscillation Amplitude of i array element, also is the amplitude weighting factor;

For the phased linear array that is made of a plurality of pipes, the deflection angle of its radiator Main beam and acoustic beam angular width are calculated by following formula: D=D ₁* D ₂(3), wherein,

$D_2\left(\mathrm{\&theta;}\right)={\left[\frac{J_0^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\cos \mathrm{\&theta;}\right)+{\cos }^2{\mathrm{\&theta;J}}_1^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\cos \mathrm{\&theta;}\right)}{J_0^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\right)+J_1^2\left(\frac{\mathrm{\&pi;a}}{\mathrm{\&lambda;}}\right)}\right]}^{\frac{1}{2}}\&times;\frac{\sin \left(\frac{\mathrm{\&pi;h}}{\mathrm{\&lambda;}}\sin \mathrm{\&theta;}\right)}{\frac{\mathrm{\&pi;h}}{\mathrm{\&lambda;}}\sin \mathrm{\&theta;}}---\left(4\right)$

D ₂Be the directivity function of pipe shape sound radiator, a and h are respectively the mean radius and the height of pipe transducer, and λ is a wave length of sound.

2, according to claim 1 a kind of in near-borehole formation the method for scanning radiation two-dimensional acoustic field, it is characterized in that: the deflection angle that enters the sonic propagation direction on stratum can change to 90 ° from-90 °.

3, according to claim 1 a kind of in near-borehole formation the method for scanning radiation two-dimensional acoustic field, it is characterized in that: the overall diameter scope of transducer array is 60mm-95mm, operating frequency range is 5kHz-25kHz.

4, according to claim 1 a kind of in borehole axis symmetry stratum the method for scanning radiation two-dimensional acoustic field, it is characterized in that: the angular width of regulating underground phased array sound radiator radiation acoustic beam is 7 °-10 °.

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