低渗砂泥岩地层的声波测井波形特征

用于低渗砂岩油气开发的压裂需要地层的纵横波时差参数;压裂形成的人工裂缝或砂泥岩中的自然裂缝是油气流入井中的主要通道.声波测井是测量地层的纵横波时差、探测连通裂缝的有效方法.本文给出了新设计的偶极子组合声波测井仪器在低渗砂泥岩地层所测量的波形.新仪器利用声波在井内传播的固有频率设计探头,利用探头阻抗随频率的变化曲线设计匹配电路,有效地提高了声发射功率,在井下采用16位A/D转换器提高了原始波形的采样精度.测量的波形比通常的声波测井波形所含的地层信息丰富.单极子长源距声波测井波形中除了通常的纵、横波和Stoneley波外,还发现了起始于纵波首波的反射波以及随深度改变其到达时间的后续波.通过与其它测井曲线综合对比发现:其反射波与井眼扩径有关,使测量的声波时差加大;后续波在显示地层特征的同时,与横波混叠在一起,使横波时差的提取变得困难.另外,在偶极子所测量的低频波形中也发现了明显的反映地层连通裂缝的反射波,该反射波可以用于指示低渗砂岩地层中的连通裂缝.

Features of waveforms of acoustic logging in the low permeability sandstone formation

For the low permeability sandstone oil production,the slowness of longitudinal wave and the transverse wave are needed in the high pressure process.The fissure to be made by the process or own in the sandstone is the passageway for oil from layer to borehole.Sonic logging is an effective tool to measure the slowness and test the fissure in the borehole.In this paper,some waveforms of the low permeability sandstone in the northwest are displayed,which are measured by a new dipole acoustic logging tool to be designed.In the new tool,the immanent frequency of borehole is used to designe the transducers.The impedance of transducer is coupled with the transmitting circuit.The sonic power is lager and 16 bits A/D are used in the sonic tool.The information recorded in the original waveforms is more.In addition to the normal longitudinal wave,the transverse wave and the Stoneley wave,there are reflected waves that begin from the first wave of waveform,and other waves which change their arrival time with the depth.The existence of these waves makes acoustic logging waveform complex,interfere with the extraction of the transverse wave slowness.Comparing with other logging curves,we find that these reflected waves relate to the expanded diameter of the well,it makes the value of the slowness larger.Moreover,in the low frequency waveforms measured by the dipole,the obvious reflected waves are obtained,which relates to the fracture of the formation.It is used to test the fissure.