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在地震频段,人们偏爱的上地壳衰减主要机制是裂隙内流体流动。在裂隙介质中,由这样的流动所产生的P波振幅方位衰减,经预测,是确实客观存在的。这一随方位变化的结果是对来自裂隙储层底部的振幅响应的修饰,由于它穿过了衰减层。其效果具有足够的强度以加剧、减弱或反转单独由反射系数引起的变化。因此,虽然这种衰减总是在垂直于裂隙走向上为最大,但是,储层底部振幅响应变暗或变亮的方向将依赖于准确的衰减规律和裂隙特征。这些因素结合得到的地震波响应,与单独用反射系数解释相比可以更恰切地判别盐水和油充填环境。遗憾的是,重复区域确实存在,流体充填的区别也只有在特定的储层和裂隙条件下才明显。衰减的振幅大到足以在小偏移距处看到,这可能解释了野外资料中观测到的P波响应随方位角明显变化的原因。
In the seismic frequency band, the main mechanism favored by the upper crust attenuation is the fluid flow in fractures. In fissured media, the azimuthal decay of P-wave amplitude produced by such a flow is predicted to exist objectively. The result of this azimuth change is a modification of the amplitude response from the bottom of the fractured reservoir as it passes through the attenuating layer. The effect is of sufficient strength to exacerbate, weaken or reverse the change caused by the reflection coefficient alone. Therefore, while this attenuation is always maximized perpendicular to the fracture strike, the direction of darkening or brightening of the bottom reservoir response will depend on accurate attenuation and fracture characteristics. The combination of these factors with the seismic response gives a more accurate discrimination of salt water and oil fill conditions than explained by reflectance alone. Unfortunately, duplicate areas do exist and the difference between fluid fill is only noticeable under specific reservoir and fracture conditions. The amplitude of the decay is large enough to be seen at small offsets, which may explain why the P-wave response observed in the field data varies significantly with azimuth.