摘要
提出了一种可用于随钻三维反射声波成像测井的圆弧片状声源,推导了该声源声学性质在波数-频率域内的数学描述,并利用实轴积分的方法对该声源在井旁地层中产生的声场进行求解,考察了声源的线度、频率等因素对该声源向地层中辐射的声场的影响.研究结果表明,特定尺寸和特定频率下的圆弧片状声源产生的纵波场的水平和垂直指向性图中仅具有一个明显的主瓣,且主瓣三分贝角宽较窄,方位分辨率较高,指向性良好,适用于随钻三维反射成像测井;SV波场和SH波场的指向性图中存在两个或者多个角瓣,SV波场在垂直于井轴方向上辐射的能量为0,另外在井中发射和接收的反射SH波场和SV波场会相互干扰,所以难以利用SV波场和SH波场进行三维反射声波成像;声源的线度和频率等因素对其辐射声场影响较大,考虑到激励效率和方位分辨率等因素,对于本文描述的井孔模型,选择圆周角在75°和90°之间,主频为12 kHz左右的声源是合适的.
We propose an asymmetric arcuate acoustic source to develop a three-dimension acoustic reflection LWD method, and deduce the mathematical description of the source in wavenumber-frequency domain. The acoustic field in the formation produced by the source is obtained by the real axis integration method, and the influences of the dimension and frequency of the source on the compressional wave field, SH wave field and SV wave field are investigated. The results indicate that only one main lobe is observed in the horizontal and vertical directivity of the compressional wave field produced by the arcuate source with specific size and frequency. The 3dB angular width of the main lope is narrow. Hence compressional wave field excited by the source is of high azimuthal resolution and suitable for the three-dimension acoustic reflection LWD. Two or more lobes exist in the directivity of SV field and SH field, and the radiant energy of the SV field at the direction perpendicular to the borehole axis is 0. Additionally, the reflected SH waves and SV waves may interfere with each other because of similar ray path and velocity.Therefore, it is difficult to image the geological structure in three-dimension by the SV field and SH field. The dimension and frequency of the source greatly impact the radiated wave field, and in consideration of the excitation efficiency and azimuthal resolution, for the borehole model described in this paper, the source with azimuthal width between 75° and 90°, and main frequency around 12 kHz is an appropriate choice.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2014年第8期2732-2742,共11页
Chinese Journal of Geophysics
基金
国家自然科学基金项目(11204380
11374371
11134011和61102102)
国家油气重大科技专项(2011ZX05020-009)
中国石油科技创新基金(2013D-5006-0304)
中国石油天然气集团公司项目(2011A-3903
2011B-4001)资助
