钻井附近地层随钻三维声速成像测井理论与方法研究

岩石的脆性对致密性油气藏开发中的压裂体积改造至关重要，这里提出一种用声学方法确定岩石脆性的研究思想。钻井过程中，由钻头撞击或应力释放等引起的井壁附近地层声速变化程度与岩石的脆性（或可压裂性）有很好对应关系，这是因为脆性好的岩石在钻头作用下容易开裂，产生的微裂隙造成岩石声速下降。本项目提出一种用随钻单极纵波测井的方位散射波反演井壁附近三维（轴向、周向和径向）地层声速成像的技术，来指导和优化致密、非均质性储层的压裂改造。根据用井孔声场和散射声场理论考察的随钻单极纵波的方位散射波振幅和相位对井壁附近声速变化的灵敏度，利用随钻方位测量的和理论计算的散射波构建目标函数，最优化约束反演不同方位的地层纵波速度径向变化剖面。上述反演方法将用来处理随钻声波内存数据，获得地层刚被钻开时井附近三维声速成像用来指导非常规储层压裂改造。提出随钻三维声波测井声系结构和工作频率的优化设计方案，将理论和方法形成应用技术。

Rock brittleness is an important parameter for hydraulic fracturing of tight formations. Here we propose an approach to determine this parameter using acoustic measurement. The formation elastic-wave velocity changes surrounding a borehole caused by drilling or stress relief are closely related to the brittleness of rock in the process of drilling. The velocity changes reflect the real rock mechanical characteristics especially when the well is being drilled. We propose to develop an LWD acoustic technology that can guide and optimize the reservoir fracturing for unconventional reservoirs. Our approach is based on mapping three-dimensional acoustic velocity variation near the borehole in the drilling environment. By studying the amplitude and phase change of LWD azimuthal scattering wave, we analyse the sensitivity characteristics in terms of radial, azimuthal, and axial velocity variations which will be used to construct an objective function for inverting the radial compressional-velocity profile in different azimuth. To solve the nonuniqueness of the inverse problem, we use a constrained inversion method. This can be done by constraining the "equivalent" damage radius estimated from monopole waveform data. This gives the near-borehole three-dimensional P-wave structure from the LWD data. Combining theoretical modeling and real data examples, we propose a plan to implement the theory and methods for field LWD data applications.