【作者】 杨大军；

【导师】 王祝文； 陶宏根；

【作者基本信息】 吉林大学 ， 地球探测与信息技术， 2007， 硕士

【摘要】 在线弹性动力学基础上,由波动方程出发,得到偶极声源激发的井孔声场,通过求解弯曲模式波的复极点,来模拟计算偶极横波声源的频散曲线,主要研究地层声参数及井眼参数对裸眼井中偶极子源激发的非对称模式波的频散特性的影响,定量分析各种不同声参数地层模型下弯曲模式波的截止频率及频散曲线的变化趋势,并对偶极子横波测井的频散效应进行校正。更多还原

【Abstract】 Pole array acoustic logging can extract approving velocity of P-wave, not extract information of S-wave in“soft formation”. At one time, as a result of dispart wave of transverse wave containning partial wave and pseudo-Rayleigh wave,it is not easy to extract information of S-wave from the full wavetrain in“hard formation”. So we have developped the array full wavetrain acoustic log by dipole acoustic source in recent decades years. With the development of modern well-logging techniques,direct shear wave logging from extracting flexure waves has become an increasingly important tool in exploration and production geophysics. Just few years ago the theory of dipole source exciting full-wave or component-wave in borehole made great progress and now it is being perfected.The dipole sonic tool has also been manufactured and applied to practice.But flexure waves is not S-wave,it is dispersive,only in extremely low frequency,it’s velocity is close to velocity of S-wave by change of frequency,when velocity of flexure waves is very loe, it’s extent is very small. So,we must proofread flexure waves in order to receive exact the S-wave velocity in rocks.We mostly complete work as follows:1. Simulated calculating full waveforms excited by dipole acoustic source in“soft formation”and in“hard formation”of doublet transverse wave log in various centre frequency and various spacing, simultaneity analysing them.2.Using partial wave field arithmetic, obtaining and drawing dispersive curve of transverse wave excited by dipole acoustic source, simultaneity analysing how the acoustic parameters and borehole parameters influence dispersive character.3.Giving correction method of dispersive curve of transverse wave excited by dipole acoustic source, realizing dispersive correction treatment of actual logging data by the program.Using wave equations,this thesis found model of the acoustic field of a borehole excited by dipole acoustic source. Applying partial wave field arithmetic,we ask for complex pole in order to simulated calculate dispersive curve of transverse wave excited by dipole acoustic source. We mostly study how the acoustic parameters and borehole parameters influence dispersive character of asymmetric mode wave excited by dipole acoustic source in soft formation and hard formation of open-hole well,including hole diameter, density of liquid in hole, density of formation, velocity liquid in hole, P-wave velocity of formation, S-wave velocity of formation. We quantitatively analyze changing tend of cut-off frequency and dispersive curve of flexure mode waves in formation model provided with various acoustic parameters, simultaneity proofread the dispersive effect of doublet transverse wave log.Applying Similitude- Sorrelation method,we change equation of flexure waves from time domain to frequency domain,so we found correction equation and correction steps of dispersive flexure waves:1. Applying time domain method ,we gain shear wave slowness in a depth point.2. Applying fast fourier transform ,we gain amplitude spectrum A（ω） of waveform data in the depth point,while we integral on A（ω） in frequency domain.3. Supposing a real shear wave slowness S S,we substitute S S into correction equation and solve it,we gain dispersive curve of flexure waves in the depth point.4. We weightedω²A²（ω） for S （ω,S_S）,and integral in frequency domain of A（ω）.We substitute 2 and 4 into correction equation,if it can not meet the equation,we repeat 3 and 4,until we gain correct solution,the shear wave slowness is real shear wave slowness.For the sake of verification of ahead theory and correction of method of dispersive correction,we correct velocity of theoretical flexure waves in order to gain velocity of shear wave in formation,and observation reliability of solution, specific as:1. First applying forward modeling method,we gain a theoretical dipole waveform in a set of data.2. We gain a“apparent velocity of shear wave”of flexure waves from synthesized dipole array waveform.3. We substitute parameters such as Vp,Vf and apparent velocity of shear wave into program,and gain corrected velocity of shear wave.4. If velocity of 3 is close to velocity of shear wave in forward modeling method,so we say our method and program is correct.We respectively aplly different parameters representing soft formation and hard formation, established a theoretical dipole waveform,gain apparent velocity of flexure waves, we substitute parameters such as Vp,Vf and apparent velocity of shear wave into program,and gain corrected velocity of shear wave,our solution is very close to real velocity of shear wave so as to error is ignored,it proves our correcting method and algorithm on dispersive is completely meet our need on dispersive correction.Apllying the program that this paper ahead introduced on correcting dispersive curve,we have treated data of cross-dipole array shear wave on some wells in Xujiaweizi area, which is truer than no-treated data .Applying theory analysis、numerical simulation and application example,we gain some conclusions:1. In dipole shear wave logging, when center frequency of sound source is very low,it can produce very pure information of shear wave,but it’s amplitude also very small.So,our center frequency of sound source is not too low.2. Whether in soft formation or hard formation, hole diameter a , hole fluid densityρ₁, formation densityρ₂,propagation velocity of sound in hole v_f, propagation velocity of P-wave in formation v_c could effect dispersive curve, change law is that higher hole diameter a and hole fluid densityρ₁ ,lower cutoff-frequency of dispersive curve;higher formation densityρ₂、propagation velocity of sound in hole v f and propagation velocity of sound in formation v c, higher cutoff-frequency of dispersive curve.But anyway effection of hole fluid densityρ₁ and formation densityρ₂ is very weak.3. Whether in soft formation or hard formation, propagation velocity of S-wave in formation v s and hole diameter a can obviously effect dispersive curve,that higher propagation velocity of S-wave in formation v_s, higher cutoff-frequency of dispersive curve,but when v_s reach a certain specific value,it’s effection is opposite.Higher hole diameter a , severer the dispersion of flexure waves. 4. Theoretical forward modeling and dispersive correction indicate that higher hole diameter a , higher our correction volume.So in the hole that hole diameter is very high,if slowness of dipole shear wave has not be corrected, error of our information is very large.We established correction formula and program on dispersive curver of transverse wave excited bydipole acoustic source,and validated it’s correctness. Practical application shows our correction formula and program can meet the log data processing,the treated slowness of S-wave accord with theoretical expectation and is close to real value.更多还原