基于逆时偏移技术的声反射波成像测井理论与实验研究

The acoustic reflection imaging logging technique is a main way to prospect the radial variation and fracture extending in the reservoir with a detection depth of tens meters around the wellbore. It is of significance to fine evaluation of reservoir and the increase of oil-gas production. Due to the limitation of traditional imaging methods in unconventional reservoirs with complex structures, in the present study we investigate the wave propagation in a strongly anisotropic heterogeneous formation outside the borehole. And a new way of three-dimensional imaging for the cracks and layers based on the reverse-time migration is proposed after theoretical and experimental research. First, the correlations between the borehole mode waves and the formation anisotropy are analyzed. The relationships among anisotropy parameters are studied based on the statistic of rock sample data. And the velocity model for the medium outside the wellbore could thus be determined by the single-well logging measurement. Then the time-reversal imaging from the reflection signals as well as the corresponding techniques of wave separation and artifact removing is investigated based on the modeling results from the finite difference time domain code. Finally, the experiments of under-water acoustics and reduced-scale sonic logging are implemented to validate the reliability and accuracy of the acoustic reflection imaging method we proposed. The research in this project has great academic significance or application values in several aspects including the development of the acoustic theory in anisotropic media, the improvement of inversion methods for sonic logging in complex formations, and the optimization of newly designed acoustic logging tool for reflection imaging.

反射波成像测井技术是了解井旁数十米范围内储层径向变化以及裂缝发育延伸情况的主要途径，对于储层精细评价、油气井增产具有重要意义。针对目前传统成像技术在具有复杂构造的非常规储层中的局限性，本项申请从理论和实验角度研究弹性波在井外强各向异性非均匀介质中的传播特性，探索利用逆时偏移技术对井外储层裂缝和层界面进行三维声波成像的新方法。具体有：第一，深入研究井中模式波速度与地层各向异性的关联，分析实测岩心数据中各向异性系数之间的相关性，提出根据单井声波资料建立井外介质速度模型的方法；第二，基于时域有限差分波场模拟结果，研究测井反射波场的逆时成像方法及相关的波场分离和减噪处理手段；第三，通过水声实验和各向异性介质模型井声学成像物理模拟，验证声反射波成像的可靠性和精度。本项目研究对于推动各向异性固体声学的发展、完善复杂储层声波测井反演方法、设计新型成像测井仪器等具有积极的学术意义或潜在的应用价值。

反射波成像测井技术是了解井旁数十米范围内储层径向变化以及裂缝发育延伸情况的主要途径，对于储层精细评价、油气井增产具有重要意义。针对此前传统偏移技术在具有复杂结构储层中的局限性，本项目探索了基于逆时偏移技术对井外层面进行三维反射波成像的新方法。从理论、数值和实验等角度，深入开展了各向异性地层井孔声场、非均匀介质弹性波传播、地层参数反演、声场仿真和并行计算、逆时偏移成像条件、波场分离和信号处理、井间反射波成像、以及随钻声波测井等多个具体领域的研究工作。获得以下主要成果：应用非均匀网格高阶有限差分和并行计算技术模拟了井外含有限尺寸裂缝的井孔声场，给出裂缝尺寸与反射波幅度的定量关系。归纳了利用单极和偶极测井资料反演横向各向同性地层弹性参数的方法，实测资料处理结果与岩心实验结果具有较好一致性。研究了考虑模式波频散的声反射波测井资料波场分离方法，可更有效地压制直达波并提取反射波。针对当前传统偶极横波远探测结果中的方位角不确定性问题，提出了利用多分量传感器接收的偏移方法、以及基于单-偶极混合采集模式的偏移方法，这两种方法从理论上均可消除反射波的周向方位不确定性，压制伪像并增强实像幅度，其中单-偶极混合采集模式还具有压制直达波幅度、拓展径向探测范围的潜力。先后通过水池反射实验、邻井反射实验以及油田现场实测资料处理，有力验证了资料处理和成像方法的有效性和准确性；给出了反射波三维成像的现场资料处理实例，获得了不同方位角反射界面的偏移图像。初步考察了井间反射波成像方法，研究了针对井间地震模型的逆时偏移成像条件和后期处理方法，根据实测资料得到反射波偏移结果与层析成像具有很好的一致性。这些研究推动了各向异性固体声学的发展、完善了复杂储层声波测井反演和成像方法；同时本项目的理论方法成果及对仪器参数的优化，指导了正在自主研发的远探测声波测井仪器的研制和测试。