东濮凹陷W405井含气砂岩弹性参数特征分析

Analysis of elastic parameters of gas bearing sandstone in well W405,Dongpu depression.

东濮凹陷文西地区储层横向变化大,气藏横向追踪困难,利用常规波阻抗反演不能解决气藏的预测问题,为此,开展了应用叠前弹性参数反演方法进行气藏预测的研究。文西地区的W405井在3529～3908m井段(沙河街组二段下部,简称沙二下)获得了工业气流,利用该井的纵波速度(vp)、横波速度(vs)和密度(ρ)3个基本弹性参数分别计算了弹性波阻抗(I_E)、γ×ρ(γ为不可压缩模量,ρ为密度)、μ×ρ(μ为刚性模量或剪切模量)、纵横波速度比(vp/vs)和体积模量(K)等5个弹性参数。利用这些弹性参数对沙二下目的层段进行了不同流体和不同岩性的直方图分析和交会图分析。结果表明,密度和体积模量对气层敏感,含气砂岩具有低密度、低体积模量的特征。利用密度与体积模量以及密度与横波速度的交会图分析可以进行文西地区气藏预测和含气丰度预测。

The reservoir of Wenxi area in Dongpu depression has a great change in horizon and is so difficult to trace the gas depos- it.Conventional acoustic impedance inversion can't solve the problem of predicting gas deposit.Aiming at this problem,the research on application of prestack elastic parameters inversion method in gas reservoir prediction is carried out.W 405 well of Wenxi area obtains commercial gas pool within the interval of 3 529～3 908 m (the lower part of Shahejie formation),five e- lastic parameters are separately calculated by applying compres- sional velocity,shear velocity and density of the well,which are elastic acoustic impedance (I_E),λ×ρ(ρfor density,λfor compressibility modulus),μ×ρ(μfor rigidity modulus or shear modulus),compressional velocity and shear velocity ratio (v_P/ v_S),and bulk modulus (K).Aimed at the target interval (the lower part of Shahejie formation),these elastic parameters are used to make histogram analysis and cross plot analysis of dif- ferent fluids and lithology.The result shows that the density and bulk modulus are sensitive to gas bearing formation and the gas bearing sandstone is characterized by low density and bulk modulus.The gas pool prediction and gas bearing abundance prediction can be carried out through the cross plots of density and bulk modulus with density and shear velocity.