基于AVO属性体的含气指数反演在致密砂岩储层的应用

Inversion of gas-bearing index based on AVO attribute and its application in compact sandstone reservoir

川东北须家河组为一套砂泥岩互层的陆相碎屑岩沉积,砂岩极其发育,但物性差,属于特低孔低渗储层,此类砂岩储层含气后,纵横波速度、密度等弹性参数没有明显变化,地震波形等异常特征微弱,仅利用叠后地震属性不能有效地进行含气检测;此外,通过流体替换试验以及正演模拟证实了该区地层含气后所引起的AVO异常较为微弱,对含气区域的刻画能力也有限。根据钻、测井资料分析可知,该区砂岩储层含气之后会引起声波时差测井值一定程度的增大,中子明显下降,有较为明显的挖掘效应。因此,这里利用中子-声波测井曲线交汇重构含气指数曲线,在AVO属性体的基础上进行含气指数反演,突出AVO属性异常,增强了AVO属性对含气性的预测能力。

Xujiahe Formation in northeast Sichuan is a set of sand shale interbedded clastic deposition of terrestrial facies,which has developed sandstones with poor physical properties,belongs to reservoir of low porosity and low permeability.In gas-bearing sandstone reservoir,there are no obvious changes in rock elastic parameters such as density,velocity of P- and Swaves,and the anomaly characteristics of the seismic waveforms is weak as well,so it cannot do gas detection effectively only by using post-stack seismic attributes.Meanwhile,fluid substitution test and forward simulation confirmed that the AVO anomaly caused by gas is relatively faint,this also result in the limited ability of depicting gas-bearing area.According to drilling and logging data,the acoustic time logging value has a certain degree of increase caused by the gas in sandstone reservoir,whilst neutron declines obviously,as well as obvious excavation effect.Therefore reconstructing gas-bearing index curve by using the neutron-acoustic logging curve intersection,together with inversion of gas-bearing index based on AVO attributes,can enhance AVO attribute anomaly and its prediction ability of gas-bearing.