向套管井外地层中定向辐射声场的数值计算

Numerical calculation on directional radiation technique to near-borehole formation through casing

针对过套管探测地层构造的工程需要,用实轴积分法研究套管井不同胶结状况下相控线阵声源在套管井外地层中激发的纵波声场。结果表明:在套管井胶结差时透射到地层中的能量减小,但在套管井任意胶结状况下,通过改变井孔中相控线阵相邻阵元间激励信号的延迟时间均可以控制井外地层中辐射声束的角宽和偏转方向,使声波沿着预先设定好的方向辐射;与单个点声源激发的声场相比,在声束主瓣角偏转方向,地层的纵波幅度得到了明显增强,这可从根本上增加来自套管井外地层声阻抗不连续界面的反射波能量,提高信噪比和探测能力;利用相控线阵声源向井外地层中定向扫描辐射声场的技术可提高对套管井外复杂地质构造的识别能力。

Aimed at the engineering requirements of measuring formation structure through casing,the acoustic fields of near-borehole formation excited by the linear phased-array source（LPAS） in cased boreholes with different bonding conditions were simulated using the real axis integration method.The numerical results show that the radiated energy to the formation in poorly-bonded conditions is less than that in well-bonded condition.But the main lobe width of the radiant beams and steered angle in near-borehole formation can be controlled by adjusting the delay time between the neighboring array elements regardless of well-bonded or poorly-bonded conditions.Compared with acoustic field excited by one point source,the P-wave amplitude for formations in the steered direction can be intensified obviously,which can strengthen the reflection energy and enhance signal-to-noise ratio of the received signal and detectivity fundamentally.The technique of the directional radiating acoustic field to the formation can improve the resolving capability and reliability of exploring the casing external complex reservoirs.