随钻方位声源的声场特征及声系设计的理论与方法研究

Azimuthal acoustic and mechanical parameters are important for exploration and production of engineering sweet spots in unconventional reservoirs. We propose an approach to determine these parameters using azimuthal source in the collar while drilling. The unipole excitation is commonly used because of its simple structure design. Although the design has azimuth sensitivity, the sound wave is complicated by multipole wave characteristics, thus causing uncertainty in the processing and interpreting of LWD azimuthal sonic data. We propose to develop a multipole decomposition analysis of source coupling mechanism for LWD azimuthal sonic logging, which can be used to guide and optimize the design of azimuthal sonic tool. The principle of multipole decomposition based on Fourier synthesis is adopted to analyze multipole coupling mechanism in LWD azimuthal sonic logging, and to solve multipole (monopole, dipole and quadrupole) contribution of sound field excited by the azimuthal source. Further, we focus on decoupling of multipole drill collar waves and formation waves excited by the azimuthal source. We analyze sound wave azimuthal characteristics by adjusting the relative position and azimuth assembly of the transmitter and receiver system. Finally, we present optimal design scheme for the sound system, and propose a plan to implement the analysis results to become an application technology.

井外岩石声学及力学参数的方位探测对非常规储层“工程甜点”的确定和油气开发至关重要，这里提出一种在钻铤上安装方位声源，利用钻井旋转实时获取储层不同方位工程参数（声速、杨氏模量等）的思想和方法。目前设计通常采用结构简单且易实现的偏心声源方式实现随钻方位测量。然而，该方式激励声场虽然具有较强方位特性，但也伴生了较为复杂的多极特性，给声波数据的处理和解释造成了较大不确定性。本项目针对随钻方位声波测井声源耦合机理提出一种多极分解的理论和方法，来指导和优化方位声波测井仪器设计与储层参数的精确获取。基于Fourier级数展开的声源多极分解理论，对随钻方位声源激发的辐射声场进行求解获得多极子（单极、偶极和四极子）成分的贡献，重点考察方位声源激发多极子钻铤波与地层波叠加声场特性，依此调整发射声源和接收相对位置及相对方位，并提出随钻方位声波测井声系结构和工作频率等参数的优化设计方案，将理论和方法形成应用技术。

声源技术的发展已成为随钻声波测井的一项重要任务，各种声源的设计也得到了实施。本项目着重研究了一种适用于随钻方位测井的瓦片状偏心声波发射换能器，利用有限元数值方法模拟了该换能器的响应特性，考察了钻铤和换能器尺寸对方位声源谐振频率及水平指向性的影响。结果表明，瓦片换能器的谐振点受自身开角和高度等因素的影响，其谐振频率随着换能器高度增加、开角增加而降低；钻铤以及换能器开角是影响随钻方位指向性的重要因素，存在钻铤以及减小换能器开角均使得井周方位分辨率明显提高。本文的工作为随钻方位发射换能器的设计提供了理论依据。.声源的多极展开是地球物理学研究的一个有趣课题，本项目采用一种基于Fourier 级数展开的声源多极分解理论分析随钻方位声波测井方位声源的多极耦合机理，对方位声源激发的辐射声场进行求解获得多极子（单极、偶极和四极子）成分的贡献，重点考察方位声源激发多极子钻铤波叠加声场的解耦分析，研究结果表明随钻测井偏心声源可以由单极、偶极和四极成分组成，并由各组成部分的贡献来表征。同时该理论分析结果得到了物理实验验证。该研究结果可为随钻声波声源的性能评价提供一种方法。