【摘要】：聲彈性現(xiàn)象是指彈性介質(zhì)在受外力作用下,聲波速度發(fā)生改變的現(xiàn)象。若干聲彈實驗研究表明巖石具有明顯的非線性效應(yīng)。通過實驗測量不同應(yīng)力作用下巖石聲速及孔周聲速分布,然后可由聲速求出巖石的三階彈性模量及判斷主應(yīng)力方向。在實際應(yīng)用中,若已知地層巖石介質(zhì)的三階彈性模量,可以通過測量地層聲速進(jìn)而求出地層所受地應(yīng)力的大小,同時已知孔周聲速分布可判斷出地層所受地應(yīng)力的方向。因此,開展巖石三階彈性模量及孔周速度分布的實驗測量,對研究反演地應(yīng)力理論與方法都具有十分重要的意義。本文通過以實驗探究為主,以聲彈理論為基礎(chǔ),分別對三種無孔巖石材料和鉆孔巖石介質(zhì)進(jìn)行聲彈性實驗。通過實驗測量單軸應(yīng)力作用下巖石縱波速度和兩個橫波速度來求解巖石的三階彈性模量。首先測量了參考態(tài)下(介質(zhì)未受應(yīng)力作用時)聲波通過介質(zhì)每個對稱面的縱波和橫波速度,通過三個對稱面的(即三個坐標(biāo)方向)縱波和橫波速度測量值,發(fā)現(xiàn)巖石樣品有弱各向異性,求出了參考態(tài)下樣品的速度各向異性參數(shù),對比Thomson參數(shù)結(jié)果看出本文實驗采用的巖石樣品近似為橫向各向同性介質(zhì)。其次改變橫波偏振方向,測量同一平面內(nèi)不同方位角處沿垂直該平面方向傳播的橫波速度,結(jié)果顯示參考態(tài)下同一平面內(nèi)沿不同方向偏振的橫波速度發(fā)生變化,進(jìn)一步確定了巖石樣品有弱各向異性。最后在理論求解三階彈性模量過程中考慮了巖石樣品參考態(tài)下的本征各向異性,并計算出不同應(yīng)力狀態(tài)下的速度理論值,然后將速度測量值與理論值進(jìn)行對比,發(fā)現(xiàn)通過巖石中心不同應(yīng)力狀態(tài)下的速度實驗值跟理論值基本吻合,說明關(guān)于巖石三階彈性模量的實驗測量需要顧及參考態(tài)的各向異性。有關(guān)巖石樣品孔周聲速的實驗探究主要集中在實驗測量孔周縱波速度分布,關(guān)于孔周橫波速度分布的實驗探究很少。本文對鉆孔的654巖樣施加垂直孔軸方向的單軸力,然后分別測量不同應(yīng)力狀態(tài)下,在孔周不同方位角處沿孔軸方向傳播的縱波速度、平行單軸力方向偏振沿孔軸方向傳播的橫波速度、垂直單軸力方向偏振沿井軸方向傳播的橫波速度。通過實驗測量了不同應(yīng)力狀態(tài)下孔周縱波和兩個橫波速度,發(fā)現(xiàn)沿孔周一圈的最大波速方向與最小主應(yīng)力方向一致,最小波速方向與最大主應(yīng)力方向一致,因此通過實驗測量孔周聲速可以確定水平主應(yīng)力的方向。
[Abstract]:Acoustoelastic phenomenon refers to the change of acoustic velocity in elastic medium under external force. A number of acoustoelastic experiments show that rocks have obvious nonlinear effects. The distribution of rock sound velocity and the sound velocity around a hole under different stresses are measured experimentally. The third-order elastic modulus of rock and the direction of principal stress can be obtained from the sound velocity. In practical application, if the third-order elastic modulus of formation rock media is known, the magnitude of in-situ stress can be obtained by measuring formation sound velocity, and the direction of in-situ stress can be determined by known distribution of acoustic velocity around holes. Therefore, the experimental measurement of the third-order elastic modulus of rock and the velocity distribution around the pore is of great significance to the study of the theory and method of inversion of in-situ stress. In this paper, three kinds of porous rock materials and borehole rock media are tested on the basis of acoustoelastic theory. The third order elastic modulus of rock is calculated by measuring the longitudinal wave velocity and two shear wave velocities under uniaxial stress. First, the velocities of sound waves passing through each symmetric plane of the medium under the reference state (when the medium is not subjected to stress) are measured, and the velocities of the longitudinal waves and the shear waves of the three symmetric surfaces (that is, the directions of the three coordinates) are measured. It is found that the rock sample has weak anisotropy, and the velocity anisotropy parameters of the sample under the reference state are obtained. The comparison of the Thomson parameters shows that the rock sample used in this paper is approximately transversely isotropic medium. Secondly, by changing the polarization direction of the shear wave, the velocity of the transverse wave propagating perpendicular to the plane at different azimuths in the same plane is measured. The results show that the velocity of the transverse wave polarized in the same plane varies in different directions under the reference state. It is further confirmed that the rock samples have weak anisotropy. Finally, the intrinsic anisotropy of the reference state of rock samples is considered in the theoretical solution of the third-order elastic modulus, and the theoretical values of velocity under different stress states are calculated, and then the velocity measurements are compared with the theoretical values. It is found that the experimental values of velocity at different stress states in the center of rock are in good agreement with the theoretical values, which indicates that the anisotropy of the reference state should be taken into account in the experimental measurement of the third-order elastic modulus of rock. The experimental investigation on the velocity of sound around the pore of rock samples is mainly focused on the measurement of the velocity distribution of the longitudinal wave around the hole, but little on the velocity distribution of the shear wave around the hole. In this paper, 654 borehole samples are subjected to uniaxial forces perpendicular to the hole axis, and the longitudinal wave velocities propagating along the hole axis at different azimuth angles around the hole are measured respectively under different stress states. The velocity of the transverse wave propagating along the hole axis is polarized in the direction of parallel uniaxial force and the velocity of the shear wave propagating along the axis of the well in the direction of the vertical uniaxial force. The longitudinal wave and two shear wave velocities around the hole under different stress states are measured experimentally. It is found that the direction of the maximum wave velocity along the circle of the hole is the same as the direction of the minimum principal stress, and the direction of the minimum wave velocity is the same as the direction of the maximum principal stress. Therefore, the direction of horizontal principal stress can be determined by measuring the velocity of sound around the hole experimentally.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O42

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