慢速地层中具有方位指向性的偶极纵波远探测测井

Far-detecting logging by oriented dipole P-wave in an acoustically slow formation

偶极远探测测井技术作为近年发展起来的一门地球物理探测技术,较单极反射纵波法具有明显的优势。针对慢速地层中的偶极辐射声场和反射声场进行了数值模拟,分析了位于充液井孔中偶极和单极声源的纵波远场辐射指向性,重点研究了偶极纵波反射声场的变化特征,验证了偶极纵波远探测方法的可行性。结果表明,偶极辐射的纵波较单极辐射的纵波具有振幅强和灵敏度高的特征,利用它可以确定反射体的空间位置和走向。结合偶极和单极纵波远探测应用效果,进一步说明了偶极纵波远探测可作为偶极声波远探测测井的一个重要补充和完善。最后,讨论了该技术在慢速地层中应用更好的可能原因,以及成像处理过程中出现的反射体方位180°不确定性的解决方法。

Single-well shear-wave imaging by a borehole dipole source, a dipole far-detecting technique, emerged in recent years as an important geophysical well-logging method and it has obvious advantages compared with previous monopole reflected P-wave meth- od. A 313 finite-difference method has been used to simulate the elastic wave-field radiation and reflection generated by a borehole di- pole source in an acoustically slow formation, analyze directionality of the P-wave far-field radiation by either dipole or monopole source in a fluid-filled borehole, and examine variation characteristics of the dipole P wave reflection field and validate its feasibility in conjunction with numerical simulation of the P-wave far-detecting acoustic imaging technique. The result shows that the dipole-gen- erated P-wave is of stronger amplitude and higher reflection sensitivity relative to the monopole one and it can be utilized to determine the dimensional azimuth and orientation of a reflector in an acoustically slow formation. The comparison of applications of both the dipole and monopole P-wave far-detecting techniques indicates that the former is of important supplement and completion for P wave remote acoustic imaging. In addition, we discussed possible reasons why its applications are better in a slow formation than in a fast formation and proposed some solutions to 180° uncertainty of the reflector azimuth in imaging processing.