未固结砂岩地震弹性性质的岩石物理模型表征研究

Rock physics modeling characteristic studies on seismic elastic properties of unconsolidated sandstone

未固结碎屑砂岩储层是国内外重要的油气储层类型之一。在地震勘探中通常使用Hertz-Mindlin(H-M)接触模型来计算未固结砂岩的等效弹性特征。由于未固结碎屑砂岩在结构上具有不规则排列特征,在弹性波作用下颗粒间的应变特征不满足H-M接触模型的基本假设,造成该模型在使用中会得到明显偏高的剪切模量值。针对这些不足,本文给出了利用切向刚度校正因子C及组合参数R/R对H-M接触模型进行修正的方法,以考虑颗粒间松弛作用及颗粒不规则性对该模型计算结果的影响。分选性是未固结碎屑砂岩重要的结构特征,利用对未固结碎屑砂岩样品实验测试结果定性分析了分选性变化对介质储集层物性特征及地震弹性特征的影响,并结合岩石物理相关理论建立了表征未固结砂岩分选性变化对地震弹性特征影响的地震岩石物理模型。

The unconsolidated clastic sandstone reservoir is one of the important reservoirs. In seismic exploration the Hertz-Mindlin contact model is often used to predict the equivalent elastic properties of unconsolidated sandstone. Due to the irregular character for the grain structure of the unconsolidated clastic sandstones, the intragranular strain characteristics under action of elastic wave does not satisfy the basic assumption of Hertz-Mindlin contact model, and then results in a relative larger shear modulus comparing to the measured data. Regarding the problem, in this paper the shear stiffness calibration factor (C) and combined parameter R/R were introduced to calibrate the Hertz-Mindlin contact model so that the side effects which the relaxation effect and intragranular irregularity cause to the calculation results of the model can be compensated. The selectivity is an important structure characteristics for unconsolidated clastic sandstones, the laboratory measured results for unconsolidated clastic sandstone samples were used to qualitatively analyze how the variation of selectivity affect physical property characteristics and seismic elastic properties, based on rock physics theory, the rock physics model which represents how variation of selectivity for unconsolidated sandstone affects seismic elastic properties was established in this paper.