不同地质条件下反演低频模型构建方法分析

Analysis on construction method of inversion low frequency model under different geological conditions

地震波阻抗反演是油气勘探开发过程中基于地震数据刻画地下储层特征及分布范围的重要工具,但受地震采集条件限制,地震数据往往是带限的,缺乏低频成分.低频成分蕴含地质构造的基本信息,缺失低频成分在一定程度上会降低基于反演数据开展储层预测的精度.因此,如何构建低频模型补偿地震低频成分就成为地震波阻抗反演的关键.首先,以均匀介质背景下的楔状模型为例,分析了低频成分对反演精度的影响;其次,结合不同学者研究成果,从碎屑岩沉积、碳酸盐岩沉积、火成岩等角度系统总结了不同地质条件下低频模型构建方法及其应用效果,对地震反演阶段根据地质条件构建精确低频模型具有一定的指导意义.分析认为:(1)碎屑岩沉积,勘探阶段钻井数量少,可采用常数低频模型、立体层析法构建低频模型;开发阶段,井资料丰富,为避免井插值引起的“牛眼”问题,视情况可分别采用井插值与地震速度和地震属性、井插值与波形反演、井插值与多重积分联合构建低频模型的方法;(2)碳酸盐岩沉积,岩性复杂、储层非均质性强,沉积相带约束构建低频模型的方法更为合适;(3)砂泥岩地层中发育的火成岩、煤层、钙层等特殊沉积体与砂泥岩地层在岩石物理特征上差异较大,可采用反演迭代法构建低频模型.依据不同沉积条件选取合适方式构建低频模型补偿低频成分,有助于提高低频模型精度,降低反演的不确定性.

Seismic impedance inversion is an important tool to estimate rock and reservoir properties from the seismic data in the process of petroleum exploration and development.Seismic data is band-limited in nature and lacks the low-frequency component.As the low frequency component holds the basic information on geological structure,the lack of low-frequency information degrades the quantitative prediction accuracy based on seismic inversion.So,it is essential to build an accurate low-frequency model to compensate low frequency information for seismic impedance inversion.In this paper,the important of low frequency model to the inversion results is studied by taking wedge model in homogeneous medium as an example.Based on research achievements of different scholars,it summarized low-frequency model building method and its application for various geological condition,such as clastic sedimentary,carbonate sedimentary and igneous rocks.The results will beneficial to build more accurate low-frequency model for seismic impedance inversion under different geological environment.The results show that(1)for clastic sedimentary,because of less drilling well in exploration stage,constant low-frequency and three-dimensional tomographic low-frequency modeling can be used.In the development stage,to avoid the“bull”problem,three methods can be applied to build low-frequency model.The first one is combining with well interpolation,seismic velocity and seismic attributes information modeling;the second is using well interpolation and wave-inversion modeling;the third is applying well interpolation and multiple integral modeling;(2)for carbonate sedimentary strong reservoir heterogeneity in vertical and horizontal,sedimentary facies controlled low-frequency modeling can be used;(3)for the strong petrophysical differences between igneous rock,coal sedimentary and the sand-shale formation,iteration method can be applied to low-frequency model building.It's beneficial to improve lowfrequency model accuracy and reduce inversion uncertainty choosing suitable method according to different sedimentary condition.