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因为含气饱和度的高低能产生非常相似的地震AVO、亮点和速度下拉异常,所以识别局部气藏比较困难。这通常可以用Gassmann理论来解释,即:(1)岩石孔隙中少量的气就能使岩石的不可压缩性大大降低,而进一步增加孔隙中的含气量,对岩石不可压缩性影响不大;(2)切变模量不受岩石孔隙中非粘性流体的影响。此外,正象通过体积平均方程预测的那样,岩石的体积密度是随含水饱和度逐渐变化的。因此,含气饱和度低的储层和含气饱和度高的储层
Because gas saturation levels produce very similar seismic AVO, bright spot, and velocity pull-off anomalies, identifying localized gas reservoirs is more difficult. This can usually be explained by Gassmann’s theory, namely: (1) a small amount of gas in the rock pores can greatly reduce the incompressibility of the rock, while further increasing the gas content in the pores has little effect on the rock incompressibility; 2) Shear modulus is not affected by non-viscous fluid in rock pores. In addition, as predicted by the volume average equation, the rock bulk density changes gradually with water saturation. Therefore, reservoirs with low gas saturation and gas-saturated reservoirs