Seismic characterization of reservoirs with asymmetric fractures
Seismic characterization of reservoirs with asymmetric fractures
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DOI：
10.1190/geo2012-0319.1
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发表时间：
2013-02
期刊：
影响因子：
3.3
通讯作者：
M. E. Far;L. Thomsen;C. Sayers
中科院分区：
文献类型：
--
作者：
M. E. Far;L. Thomsen;C. Sayers
反射振幅随偏移量和方位角的变化对天然裂缝和诱发裂缝的存在很敏感。我们从宽方位角噪声合成pp反射数据中测试了裂缝柔度矩阵分量的反演。该模型为单斜对称裂缝型储层，由两组垂直不对称裂缝嵌套在VTI背景中形成。假设裂缝（关节）是垂直的，具有非圆形和/或不对称剪切顺应性。综合反演结果表明，对裂缝剪切对称性的错误假设（例如，将不对称裂缝视为旋转不变裂缝）会导致裂缝柔度矩阵的估计出现相当大的误差。单斜对称介质（考虑分层和多裂缝集）的有效二阶和四阶裂缝柔度矩阵的分量可以用作与裂缝介质特征相关的属性。使用蒙特卡罗模拟来测试先验信息（关于未破裂岩石的背景VTI参数）中的不确定性的影响，因为它们影响这些属性的反演。根据这一分析，在蒙特卡罗模拟中实现了快速剪切波极化方向的稳健反转。虽然蒙特卡罗模拟得到的裂缝柔度矩阵各分量的平均值与正演模拟的实际值一致，但蒙特卡罗模拟得到的单个值对背景性质的不确定性很敏感。由于没有裂缝的背景VTI介质的弹性性质（或其他方位角可变特征）不会引起反射系数随偏移量变化的方位角变化，因此同时反演背景性质和裂缝张量分量需要额外的约束条件。
Variations of reflection amplitude with offset and azimuth are sensitive to the presence of natural and induced fractures. We tested inversion for fracture compliance matrix components from wide azimuth noisy synthetic PP-reflection data. The model was a fractured reservoir with monoclinic symmetry, formed by two sets of vertical asymmetric fractures embedded in a VTI background. The fractures (joints) were assumed to be vertical, with noncircular shape and/or with asymmetric shear compliance. Results of synthetic inversion showed that an incorrect assumption about fracture shear symmetry (e.g., treating asymmetric fractures as rotationally invariant fractures) can cause considerable error in estimation of the fracture compliance matrix. Components of effective second- and fourth-rank fracture compliance matrices for a medium with monoclinic symmetry (which takes into account layering and multiple fracture sets) can be used as attributes related to the characteristics of the fractured medium. Monte Carlo simulation was used to test the effect of uncertainties in the a priori information (about background VTI parameters of unfractured rock), as they affect inversion for these attributes. According to this analysis, the direction of fast shear-wave polarization was inverted robustly in the Monte Carlo simulation. Although the average values of the components of fracture compliance matrices obtained from Monte Carlo simulation were in agreement with the actual values used for forward modeling, individual values obtained in Monte Carlo simulation were sensitive to uncertainties in the background properties in general. Because the elastic properties of background VTI media without fractures (or other azimuthally variable features) do not cause azimuthal changes in reflection coefficient variation with offset, simultaneous inversion for background properties and fracture tensor components require additional constraints.