过套管方位远探测声波成像测井理论与方法研究

用井中声源探测井外几十米范围隐蔽油气藏的远探测测井技术已成为深层油气勘探开发的“利器”，在套管井中进行井外远探测对于老油田漏失的油气层重新挖潜与改造以及保证高风险超深井的安全测井等意义重大。但与裸眼井情况相比，受钢套管屏蔽和水泥胶结状况等不利因素影响，套管井中的声场辐射/接收更复杂，井外反射波信噪比更低，过套管声波远探测实现高质量成像具有挑战性。本项目基于偶极声源与套管/水泥环/地层耦合机理，提出一种套管井中声源辐射效率和方位接收灵敏度的远探测理论与计算方法。建立柱状分层套管井模型，根据复坡印廷矢量原理，定义辐射能流与导波能流比值为井中偶极声源的辐射效率，由该参数优选套管井中偶极声源的优势频段；基于远场反射波在井中多极分解理论，模拟分析井中方位接收灵敏度；开展不同胶结状况套管井中偶极横波辐射效率和井中反射波幅度信噪比及方位灵敏度的理论和实验研究，指导过套管方位远探测声波测井仪器设计与研发。

The borehole acoustic reflection imaging using acoustic source-receiver system in a borehole to detect hidden oil and gas reservoirs away tens of meters from well has become a "sharp weapon" for deep oil and gas exploration and development. It is of great significance to refresh and transform the old wells and ensure the safety logging in high-risk and ultra-deep wells. However, compared with the situation of open-hole, due to acoustic shielding of steel casing and cement bonding condition, the acoustic radiation/reception field in the cased well is more complex, the signal-to-noise ratio of the reflected wave signal away from borehole is more lower, so it is challenging to achieve high-quality imaging through cased well. Based on the coupling mechanism between the dipole source and casing/cement/formation, this project presents a borehole acoustic reflection imaging theory and modeling method for the acoustic source radiation efficiency and azimuthal reception sensitivity in the casing well. We firstly stablish a radially layered casing well model, and define the ratio of radiant energy flow to guided wave energy flow as the radiation efficiency of the dipole source in the well according to the complex Poynting vector principle. From this parameter, the optimum excitation frequency of the dipole source in the cased-well is optimized. Based on the multipole decomposition theory of reflected wave response in borehole, the azimuthally receiving sensitivity in the borehole can be simulated and analyzed. Carry out detailed theoretical and experimental studies on the radiation efficiency of dipole shear wave in far-field with different cementation conditions, the signal-to-noise ratio and the azimuthal sensitivity of the reflected wave amplitude away from borehole, and guide and optimize the design and development of the sonic logging tool for azimuthal borehole acoustic reflection imaging through casing.