随钻声波测井双源反激隔声方法及实验研究

The design of isolator is the key technology of acoustic logging while drilling (LWD). The essence of LWD isolation is to suppress tool waves propagating along the drill collar. The LWD acoustic isolator usually is achieved by periodically cutting grooves along the drill collar between acoustic transmitter and receivers. Such technique, although is effective, reduces the mechanical strength of the drill collar and cannot eliminate low-frequency tool waves. Based on the destructive interference theory, this project proposes a dual source of opposite polarity technique to solve the tool wave problem considering the coupling effect between transmitting transducer and drill collar. This technology does not use the groove-cutting design and can widen the isolator frequency-band range. Based on the acoustoelasticity and acoustic couple theory, we derive the LWD modes wave characteristics of the dual source. In the next, we confirm the main controlling factors of suppressing tool waves based on the wave field analysis. Using multiparameter constrained inversion and deconvolution method, we achieve the optimal structure design of the dual source of opposite polarity. Finally, we carry out the experimental platform of LWD tool and test double source system in the laboratory. We further propose an acoustic system and source excitation scheme, providing theoretical guidance and technical support for the originally LWD instrument developing.

隔声技术是随钻声波测井的关键，其核心是钻铤波消声。通常，采用在发射和接收换能器间钻铤刻槽来衰减钻铤波，但刻槽会降低钻铤强度，同时因钻铤尺寸限制，不能有效阻隔低频率的钻铤波。本研究根据声波相消性干涉原理，提出一种考虑发射换能器和钻铤耦合作用机理的双声源延迟反向激励方法（简称双源反激）来实现钻铤波的压制，不需要对钻铤刻槽隔声，且可以拓宽隔声阻带。根据声弹性理论和声波耦合理论，求解双源反激随钻声波测井井孔声场，通过声场特征和数值模拟分析，研究钻铤波压制的影响机理；构建优化目标函数，采用多参数约束反演和反褶积理论，优化设计双声源结构及其激励方法；构建随钻声波测井隔声测试系统，开展双源反激隔声物理实验，给出最佳双源反激隔声效果的随钻声波测井声系设计方案和声源激励方法，为双源反激随钻声波测井仪器研发提供理论指导和技术支持。

随钻测井（LWD）是近年来迅速崛起的先进技术。它集钻井技术，测井技术和油藏描述等技术于一体，在钻井的同时完成测井作业，从钻井测井一体化中节省成本。跟常规电缆测井相比，除了节省成本外，随钻测井还具有地层信息更加准确、地质导向和风险预估、适合大斜度井和水平井等优点。然而，随钻测井技术一方面增加了钻井钻进和泥浆液循环等干扰噪声，另一方面对仪器整体强度提出了更高的要求，因而电缆测井仪器中的刻槽隔声技术不再适应。基于此，提出一种考虑发射换能器和钻铤耦合作用机理的双声源延迟反向激励方法（简称双源反激）来实现钻铤波的压制。首先建立同时考虑声波发射换能器和钻铤结构的随钻声波测井有限元模型，对单声源和双发射声源延迟反向激励下沿着钻铤传播的声波信号进行数值模拟，得出了声源激励频率、双源延迟时间及激发幅度对钻铤波幅度的影响。其次，基于发射换能器和钻铤的相互耦合机理，确定了声源激励经换能器作用于钻铤后的转换关系，建立了等效声源激励函数，理论推导出双源反激随钻声波测井声场的解析表达式，从而通过理论计算出双源反激随钻声波测井的钻铤波响应特征，并与有限元数值模拟结果对比验证。再次，考察各种影响因素对钻铤波和地层波的影响，构建双发射声源激励频率、延迟时间和激发幅度共同影响下钻铤波幅度的目标函数，利用快速模拟退火法对多个声源参数进行约束反演，优化设计出声源结构尺寸参数，从而利用反褶积理论构建出最佳隔声效果的声源激励波形函数。最后，设计出一种双源反激随钻声波测井的声系结构，即在现有单声源随钻测井科研样机的基础上，增加优化设计的双声源结构和与之匹配的激励信号源，开展了双源反激随钻隔声物理实验，并与理论设计结果相互验证，最终给出最佳双源反激隔声效果的随钻声波测井声系设计方案和激励方法。该项目的实施能够为双源反激随钻声波测井仪器研发提供理论指导和技术支持，有助于加快我国随钻声波测井技术的进步。