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本文利用P波和S波反射数据描述第三系Upper Green River组天然裂隙气藏的方位各向异性并阐述两种数据体的优点和能力。目的是评估P波地震资料检测气充填裂隙的可行性,估算裂隙密度和方位,并与S波的结果作比较。垂直裂隙的P波响应必须根据不同炮-检方位(传播路径)与裂隙走向的角度进行分析。两条多分量反射资料的测线埋置为近似平行和垂直Upper Green River组裂隙的主方向,该方向由露头岩芯分析和测井数据成像确定。根据数据的叠前振幅随偏移距变化(AVO)分析P波振幅响应并与Upper Green River气砂岩/盐水砂岩各向同性模式的AVO作比较。另外还采集了九分量的垂直地震剖面(VSP)的资料,利用P波反射标定S波反射并佐证反射S波勘探成果。 反射资料的快横波S1分量的方向和VSP资料的S1分量的方向一致,在Upper Green River组裂隙方向为NW(北西向),这与最大水平应力方向和测井的椭圆率方向相同。平行和垂直Upper Green River组裂隙观察的P波AVO梯度之间有明显的差别。当传播路径垂直裂隙时,P波AVO梯度值为正,并与产气层裂隙有关。在含水层区,AVO梯度接近于零和负值。在裂隙层顶部观测的P波AVO梯度的方位变化与裂隙层内S波分裂(S波各向异性)的垂直旅行时之间的时差存在一定的比例关系。
In this paper, the azimuthal anisotropy of the natural fissured gas reservoirs in the Tertiary Upper Green River Formation is described by P-wave and S-wave reflection data and the advantages and abilities of the two data bodies are described. The purpose is to assess the feasibility of P-wave seismic data for the detection of gas-filled fractures, to estimate fracture density and orientation, and to compare them with S-wave results. The P-wave response of a vertical fracture must be analyzed from the angle of different gun-check positions (propagation path) and fracture direction. The lines of the two multi-component reflections are buried into principal directions parallel to and perpendicular to the fissures of the Upper Green River Formation as determined by outcrop core analysis and logging data. The P-wave amplitude response was analyzed based on the prestack amplitude of the data as a function of offset (AVO) and compared with the AVO of the isotropic model of the Upper Green River gas-sandstone / salt sandstone. In addition, nine-component vertical seismic profiles (VSPs) were collected, and the S-wave reflections were calibrated using P-wave reflections and the results of S-wave reflection were confirmed. The direction of the fast shear-wave S1 component of the reflection data coincides with the direction of the S1 component of the VSP data, and NW (NW) in the fracture direction of the Upper Green River, which is the same as the direction of the maximum horizontal stress and the ellipticity of the well logging. There is a clear difference between the P-wave AVO gradients observed in the fissures of the parallel and vertical Upper Green River groups. When the propagation path is vertical, the P-wave AVO gradient is positive and related to the gas-bearing fracture. In the aquifer zone, the AVO gradient approaches zero and negative values. There is a certain proportional relationship between the azimuthal variation of P-wave AVO gradient observed at the top of the fissure layer and the vertical travel time of S-wave splitting (S-wave anisotropy) in the fissure layer.