Quantitative analyses of seismic responses of karst cave reservoir play an important role in predicting and imaging this kind of reservoirs. Ignoring the multiples and based on sonic equation, the analytic expression of the seismic response for an isolated karst cave of small size was given here. The relationship among the size and fillings of the karst cave and the seismic amplitude attribute was established by this analytic expression. The results of analysis indicated that: (1) reflection amplitude is directly proportional to the volume of the cave when the size of the cave is less than 1/8 of the seismic wavelength; (2) the impact of the horizontal size on the reflection amplitude is mainly controlled by Fresnel radius, and also the variation law of amplitude with horizontal size is affected by the vertical size; (3) the impact of vertical size on reflection amplitude behaves as tune effect, and the strongest amplitude appeared in case that the vertical size is equal to the tune thickness (1/4 of the seismic wavelength). The following results of the numerical simulating studies on caves with varied sizes, and physical modeling experiments on cave groups and caves with varied infillings also supported the conclusions.%定量分析碳酸盐岩孔洞型储集体的地震响应特征,对孔洞储集体的预测和刻画研究有着重要意义.基于声波方程,在忽略多次散射的情况下,导出了深层小尺度孤立洞体的地震响应近似解析式,该解析表达式给出了孔洞尺度、充填程度与地震振幅属性之间的关系.分析表明:(1)当孔洞异常体尺度小于地震波长的1/8时,反射波振幅与异常体体积呈近似正比关系；(2)异常体横向上的尺度对反射波振幅的影响主要由菲涅耳半径控制,同时振幅随横向尺度的变化规律受到纵向尺度的影响；(3)异常体纵向上的尺度对反射振幅的影响主要表现为调谐效应,当纵向上的尺度等于调谐厚度(地震波长的1/4)时,反射振幅最强,不同尺度溶洞的数值模拟研究结果以及不同填充物的单洞物理模型试验和溶洞群物理模型试验验证了以上结论的正确性.
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