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    双相复杂裂缝介质精细反演方法

    High-precision inversion method for two-phase complex fracture medium

    • 摘要: 裂缝是油气存储及运移的通道之一,也是矿井灾害的诱导因素之一,裂缝的精细刻画有助于资源安全高效地开发。传统裂缝介质反演通常假设裂缝为水平或者垂直形态,不符合裂缝的天然形态,利用近似解求解裂缝的微弱地震响应容易造成误差,且单相介质假设不符合含气和水等储层的地质情况。鉴于这些问题,提出了基于线性滑动理论的双相复杂裂缝介质精确Zoeppritz反演方法。介绍了双相介质流体替换及弹性参数计算方法,柔度参数可用于描述裂缝特征,将其引入到Zoeppritz方程中,可以推导任意角度双相裂缝介质的反射系数和透射系数。基于线性滑动理论,分析了双相介质裂缝及阻抗界面引起的地震响应特征,阐明了裂缝界面的地震波能量分配问题。鉴于裂缝及阻抗界面地震反射波的能量差异,提出了精确解和近似解的综合多尺度反演流程。合成及实际数据测试结果表明,提出的反演方法可以同时获得高精度的纵、横波速度、密度、法向柔度及切向柔度参数,在裂缝空间展布的基础上预测裂缝属性参数,相较于传统反演方法具有更高的计算效率和精度,可以为油气勘探开发及CO2地质封存探测等提供有效的技术支撑。

       

      Abstract: Fractures serve as the channel of oil and gas storage and migration, and they are factors that induce mine disasters. Therefore, a detailed characterization of fractures contributes to resource security and effective development. Traditional fracture medium inversion usually assumes that the fracture is horizontal or vertical, which is not consistent with the natural morphology of the fracture. Using approximate solutions to solve the weak seismic response of the fracture is prone to errors, and the single-phase medium hypothesis is not in line with the geological conditions of reservoirs containing gas or water. To address these issues, an exact Zoeppritz inversion method based on linear slip theory was proposed for two-phase complex fractured media. The fluid replacement and the calculation method of elastic parameters in two-phase media were introduced. The compliance parameter, which could describe the fracture characteristics, was input into the Zoeppritz equation, and the reflection and transmission coefficients of the two-phase fractured media at any angle were derived. Based on the linear slip theory, the seismic response characteristics caused by the fracture and impedance interface of two-phase media were analyzed, and the problem of seismic wave energy distribution at the fracture interface was explained. In view of the energy difference of seismic reflection wave between fracture and impedance interface, a comprehensive multi-scale inversion flow of exact and approximate solutions was proposed. The test results of synthetic and field data show that the proposed inversion method can simultaneously obtain high-precision parameters of P- and S-wave velocities, density, and normal and tangential compliances and predict fracture attributes on the basis of fractures’ spatial distribution. The method has higher computational efficiency and accuracy than the traditional inversion method and can provide effective technical support for oil and gas exploration and development, as well as for the detection of CO2 geological sequestration.

       

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