基于修正近似公式的HTI介质高分辨率AVAZ非线性反演理论与方法研究

Under long-wavelength assumption, shale reservoirs with vertical fractures can be approximately equivalent to horizontal transverse isotropy (HTI) media. The existing pre-stack inversion methods for HTI media generally have problems such as low accuracy and poor applicability, which cannot meet the requirements of exploration and development of typical unconventional reservoirs such as inter-salt shale oil. Therefore, it is of great theoretical significance and practical value to carry out research on the high-resolution inversion theory and method of HTI media. In order to improve the calculation accuracy of forward operator of inversion algorithm, the new nonlinear modified approximate formulas of reflection coefficients of HTI media are derived in this project. The idea of blockiness constraint inversion and frequency division joint inversion is introduced for better solving the problem of parameter inversion of inter-salt shale oil and other reservoirs with rhythmic layer structure. Effective enhancing the contrasts between layers and making full use of the high frequency seismic information contained in seismic data can further improve the acquisition accuracy of shale reservoir parameters. In addition, combining with the improved rock physics relationships, the direct high-resolution inversion of reservoir stress and fracture parameter information will be achieved, which can provide reliable and accurate seismic inversion results for the final shale reservoir sweet spot prediction and the fine description in the later stage of exploration and development. This research is benefited for the further study. It can promote the application of prestack inversion technology in the actual exploration and development of shale reservoirs.

长波长假设条件下，发育垂向裂缝的页岩储层可近似等效为HTI介质，现有针对HTI介质的叠前反演方法普遍存在精度低、适用性差等问题，不能满足盐间页岩油这类典型非常规储层勘探开发的要求。因此，开展HTI介质高分辨率反演理论与方法研究，具有重要理论意义和实用价值。项目从提升反演算法正演算子计算精度的角度出发，推导一种新的HTI介质反射系数方程非线性修正近似公式。为了更好地解决以韵律层结构为主的盐间页岩油等储层的参数反演问题，有针对性地引入块约束反演和分频联合反演的思想，有效突出地层边界特征和充分利用地震数据中包含的高频地震信息，进一步提升页岩储层参数的获取精度。此外，结合改进的岩石物理关系，实现储层地应力和裂缝参数信息的直接高分辨率反演，为最终的页岩储层甜点预测和勘探开发后期的精细描述提供可靠且精度适宜的地震反演结果。项目研究对推动叠前反演技术在页岩储层实际勘探开发中的应用具有十分重要的意义。

随着油气勘探开发工作的不断推进，各向异性反演已成为非常规油气储层获取储层参数的重要地球物理反演技术之一。地震反演结果能够为储层精细描述、页岩储层“甜点”预测等油藏开发工作提供重要的数据支撑，如何更高精度地获取储层参数的反演结果一直是地震反演研究的重点。对此，本项目重点开展了针对非常规储层的储层参数高精度反演研究。基于由简入繁，循序渐进的研究思路，首先开展了基于精确Zoeppritz方程的储层参数高精度非线性反演，为各向异性多参数非线性反演奠定了良好的反演理论基础。然后将反演方法推进至相对简单的VTI各向异性介质，开展了基于VTI介质高阶非线性简化近似方程的各向异性反演研究，验证了五参数同时非线性反演估计的可行性，并以此为基础进一步开展了基于VTI介质精确反射系数方程五参数同时非线性反演，有效克服了近似公式固有缺陷对目标参数反演精度的限制，提升了各向异性参数的估计精度。最后结合岩石物理理论，开展了基于粘弹性Chapman-Kelvin新模型的裂缝储层频变AVAZ反演研究，探讨了基于改进岩石物理模型的裂缝预测。合成数据和实际数据测试表明，基于贝叶斯理论的确定性反演方法能够成功解决由强非线性正演方程（精确Zoeppritz方程、精确VTI反射系数方程）构建的非线性反演问题，提升储层参数的估计精度，为后续开展基于HTI、TTI等复杂介质精确反射系数方程的强非线性反演研究奠定了理论基础。频变AVAZ裂缝储层参数反演研究表明，MCMC随机反演方法在缺失先验储层参数信息时，反演结果的不确定性较强。但当存在有效且足够的先验信息时，能够进一步提升反演结果的可靠性。而贝叶斯理论直接反演方法，则显示出基于频变AVAZ信息来区别大尺度裂缝和微尺度裂隙的潜力。上述研究结果表明，本项目取得的一系列研究成果能够解决具体实际问题，达到提升储层参数估计精度的目的，对于丰富和发展地震反演理论具有重要的理论和实际意义。