含气地层的AVO响应分析——以苏4井为例

岩石的孔隙度、流体饱和度等信息是影响地震波振幅随炮检距变化（AVO）的重要因素。根据苏4井全波列测井数据，利用Gassmann方程对含气地层进行了流体替代计算，分析了孔隙度及含气饱和度变化对地层AVO的影响。AVO响应分析表明，对于苏4井低孔隙度石英砂岩储层，孔隙度的变化对AVO的影响要大于流体性质的影响。当含气饱和度为定值，孔隙度小于8％时，其阻抗大于上覆泥岩阻抗，表现为高阻抗气层；孔隙度大于8％时，表现为近零阻抗和低阻抗气层。AVO截距（P）与斜率（G）的交会分析表明，当孔隙度较小时，G属性对含气饱和度变化敏感；大孔隙度时，P属性对含气饱和度变化敏感。

AVO analysis on gas-bearing layer

The porosity and fluid saturation of rock are key factors influencing AVO. Based on full wave train log of Su4, using Gassmann fluid substitution, the influence of porosity and gas saturation on the velocities, density and Poisson ratio in the reservoir are studied. The analysis of AVO shows that the change of porosity has more influences on AVO response than gas saturation does. The gas saturation keeps constant, the gas layer behaves high impedance when Porosity is less than 8%; it behaves zero or low impedance when porosity is greater than 8%. P-G crossplot analysis shows that G attribute is sensitive to gas saturation when porosity is lower; when porosity is high, P attribute is sensitive to gas saturation.