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大部分井下声波测井的理论研究都应用无限实体中流体井眼的简单模型。这种研究试图用更复杂的模型来考虑侵入带对声波波列的影响,该模型由井眼周围的几个有限同轴壳体组成。适当地选择这些柱状壳体的物理参数,可以研究侵入带、泥饼或套管对声波波列成分的影响。这种模型考虑了几何衰减,但它假设地层是理想的弹性体。探讨的主要问题是声波测井的探测深度。本文主要研究侵入带、泥饼或钢套管对全波列成分(纵波、横波、反射模式和斯通利波模式)的影响。可以推断声波测井仪具有非常浅的探测深度。对于纵波和横波,这一深度取决于源距(声源和接收器之间的距离)。根据经验,若源距为n英尺,则声波测井的探测深度为n英寸。这样,普通声波测井仪的探测深度小于6英寸。由于纵波和横波首波幅度的衰减限制了实际的声源和接收器之间的距离,因此声波测井的最大探测深度为2英尺。故声波测井仪通常只能探测侵入带的特性。
Most of the theoretical studies of downhole sonic logging have applied simple models of fluid wellbores in an infinite body. This research attempts to consider the impact of invaded bands on acoustic wave trains with a more complex model consisting of several finite coaxial shells around the wellbore. The proper selection of the physical parameters of these cylindrical shells allows the study of the effect of invaded bands, mud cakes or sleeves on the acoustic wave components. This model considers geometric attenuation, but it assumes that the formation is the ideal elastomer. The main issue to be explored is the sounding depth of the acoustic logging. This paper mainly studies the influence of invaded zone, mud cake or steel casing on the components of the full wave train (longitudinal wave, shear wave, reflection mode and Stoneley wave mode). It can be inferred that sonic logging tools have a very shallow depth of investigation. For longitudinal and shear waves, this depth depends on the source distance (distance between source and receiver). As a rule of thumb, if the source is n feet apart, the acoustic logging depth is n inches. In this way, conventional sonic logging tools have a probing depth of less than 6 inches. Since the attenuation of the first amplitude of the P-wave and S-wave limits the actual distance between the sound source and the receiver, the maximum sounding depth of the acoustic logging is 2 feet. Therefore, acoustic logging tools usually only detect the characteristics of intruding bands.