油气层低频异常的数值模拟与应用

含不同流体的储集层对地震波具有不同的频率响应。含有烃类的储集层与含水储集层相比,对地震波的低频成分有特殊的响应,即出现低频振幅异常现象。为了分析产生这种现象的机理,建立了一系列薄储集层模型。通过Gassmann方程来计算储集层孔隙度变化及孔隙流体改变时的纵波速度和密度,并用谱分解来从合成的地震数据中提取特征频率成分并识别低频异常。通过数值模拟与实际资料分析显示,地震波穿过含气层时速度比穿过背景层时低,引起薄储集层产生低频振幅异常现象。

Numerical Simulation of Low-Frequency Amplitude Anomaly in Reservoirs and Its Application

The reservoirs with different fluids appear different responses of seismic wave frequency.And the reservoirs with hydrocarbons have special responses to low frequency of seismic waves compared with the reservoirs with water.This phenomenon is called low-frequency amplitude anomaly.This paper develops a series of models of thin reservoirs for analysis of mechanism of such a phenomenon by Gassmann equation,including the calculation of varied reservoir porosity,P-wave velocity and density at pore fluid changes.The spectrum decomposition is applied to collecting the characteristic frequency component from synthetic seismic information for identification of the low-frequency amplitude anomaly.The numerical simulation and real data analysis indicate that the velocity of seismic wave penetrating gas-bearing zone is lower that that of penetrating background zone,thus causing thin reservoirs to appear the phenomenon of low-frequency amplitude anomaly.