井下三维声波定向扫描接收方法研究

Acoustic transducer’s reception is one of the most important scientific subjects of downhole acoustic measurement. Monopole and dipole vibration modes of downhole acoustic logging transducers currently used in downhole tools have limitations of omni-directivity and multiple-solution in inversion. It is apparent that the performance acoustic phased array transducer applied in fluid filled wellbores is better than of the conventional transducer. This application proposes a downhole scanned 3D directional reception (downhole beamforming) method that can receive acoustic signals from arbitrary azimuths in 3D space based on phased cylindrical arrays. The study is planned to investigate and evaluate cylindrical receiver array parameters of the spacing, frequency, amplitude weighting and phase weighting factor etc. and how they affect directivity and band width which can optimize scanned 3D directional reception. The advantages of proposed downhole scanned 3D directional reception method can be analyzed and verified through comparison between numerical simulations and experimental measurements. We expect that the application of 3D scanned directional reception method in downhole will increase investigation depth of downhole acoustic measurement, enhance orientation resolution, exclude multi-solution of evaluation, and finally improve petroleum exploration capability in complex and heterogeneous reservoirs. The research results may have broad application prospects in wireline acoustic logging and LWD acoustic logging.

声波的接收是井下声波测量的重要科学问题之一。目前井下应用的单极子和偶极子振动模式的声波测井换能器存在无明显指向性和反演多解性的问题。在井下使用声波相控阵技术有望突破常规井下声学测量方法的局限。本申请拟设计和制作声波测井柱面接收换能器阵列，提出和研究一种可定向接收来自任意方向入射声波信号的三维定向扫描接收方法即井下波束形成方法。通过数值模拟和实验测量考察柱面声波接收阵的阵元间距、工作频率、相位和幅度加权方式等相控阵参数对声波接收器的指向性、成束角宽的影响，进而优化声波接收阵设计。通过理论研究和实验测量的对比分析来考察和校验三维定向接收方法的分辨率、准确性等。预期在井下应用三维定向接收方法有利于增大井下声学测量的探测深度、提高空间分辨率，排除测量评价结果的多解性，提高复杂、非均质油气藏的勘探能力,在电缆声波测井和随钻声波测井中具有良好的应用前景。

声波的接收是井下声波测量的重要科学问题之一，本项目研究了一种基于相控阵的可定向接收来自任意方向入射声波信号的井下三维定向扫描接收方法即井下波束形成方法。.分别开展了无限大流体中和井下相控阵声波定向扫描接收方法的数值模拟，重点考察了相控阵类型、阵元个数、阵元间距等参数对定向接收效果的影响。研究结果表明，相控线阵的阵元个数越多、阵元间距越大，定向接收指向性越强，但当间距大到一定程度后就会产生旁瓣，定向接收效果变差；采用相控圆弧接收子阵工作时，可以定向接收在水平面内任一特定方向入射到相控圆弧阵的平面波，且定向接收效果比各接收单元独立接收时好，而当采用三/四阵元接收子阵结合的工作方式时，其定向接收效果更好些；将相控线阵和相控圆弧阵结合起来组合成相控柱面阵，可以扫描接收三维空间中任意方向入射而来的声波，从而可以准确地判断出三维空间中声波的入射方向。.为了展开井下声波信号扫描接收方法物理模拟实验，制作了由接收换能器柱面阵、多通道数据放大和数据采集等电子线路构成的实验测量系统，进行了包括八单元接收器接收单个方向入射波实验和八单元接收器接收多个方向入射波等方面的模拟实验。对实验测量的多通道波形进行了扫描接收处理(波束成形处理)，实验结果表明，采用三阵元和四阵元圆弧阵的组合接收模式所获得的接收指向性强于采用三阵元圆弧阵或者四阵元圆弧阵接收模式。由八单元接收器接收多个方向入射波实验通过扫描接收得到的入射波的方向与实际声波入射方向一致。.将三维声波定向扫描接收方法应用到新一代声波测井仪器的数据处理中，对现场测量数据进行了处理和方法校验，处理实例说明，该方法可以显著地提高方位反射声波测井的井旁反射体方位测量准确性和成像质量。本项目所取得的研究成果应用到井下声学测量有助于提高井下声学测量的空间分辨能力、排除测量评价结果的多解性，提高复杂、非均质油气藏的勘探能力，在电缆声波测井和随钻声波测井中具有良好的应用前景。