双相介质井孔多极源声测井理论及分波分析与全波计算

THEORY OF ACOUSTIC MULTIPOLE LOGGING AND ANALYSIS OF WAVE COMPONENTS AND CALCULATION OF FULLWAVEFORMS FOR TWO-PHASE MEDIUM FORMATION

用Ｂｉｏｔ双相介质模拟油储层，对井孔中多极声源激发的声波场进行了系统的理论推导、分波分析和全波计算．对模式波作了通常的频散分析，特别强调了激发特性对模式波传播行为的影响．并着重对临界折射Ｐ波和Ｓ波的激发特性在不同地层［硬地层（地层横波速度大于井中流体声速）和软地层（地层横波速度小于井中流体声速）］和不同频段进行了分析和对比；讨论了井径、孔隙度和渗透率对各分波的影响；频域的分波分析还与时域的全波计算相对照．通过数值分析得出：在孔隙地层下，无频散的临界折射Ｓ波也是控制低频（偶极或四极源）直接横波测井的主要机制．

The reservoir is modeled by a two-phase medium based on Biot and homogenization theories, and the acoustic field excited by a acoustic multipole source in a fluid-filled borehole is systematically derived and numerically simulated. Not only has the usual analysis on the mode waves been conducted, but the effect of the excitation of the mode waves on the propagation mechanism has also been emphatically analyzed. The excitation characteristics of the critical refracted P and S waves in the fast and slow formations and the effect of radius,porosity, permeability and other factors on the wave components are also investigated. The analyses of wave components in the frequency domain and the simulatinns of the full-waveforms in the time domain are carried out. In the porous formation, the mechanism of the direct shear wave logging in the low-frequency range is studied. It is pointed that the critical refracted S wave which has no dispersion is the dominant component in the direct shear wave logging with the low-frequency multipole source (dipole and quadrupole).