随机建模中变差函数的敏感性研究

Sensitivity of variogram in stochastic modeling

变差函数是随机建模中最重要的参数,它决定随机模拟结果中砂体的空间展布、储集层的物性和砂体的体积。在详细解剖M油田的砂体几何形态的基础上,对比分析球模型、指数模型和高斯模型的计算结果,3种模型计算的变差函数长变程误差15％,短变程误差25％,方向也不一样;同时运用不同模型计算的砂体体积亦有较明显的差别:砂体越发育,砂体连通性越强,不同模型计算的砂体体积相差越小;砂体越不发育,砂体连通性越差,不同模型计算的砂体体积相差越大。通过对变差函数的应用改进,提出空变变差函数的概念,即平面上变差函数是变化的,应用空变变差函数计算结果提高了随机建模的可靠程度。

Variogram is a vital parameter in stochastic modeling, determining sand distribution, petrophysical property and volumes. Based on the measure of sand geometry in M Block and comparison of results calculated with Spherical, Exponential and Gaussian Model, it is concluded that different variogram models get very different variogram range in major and minor direction. The difference of the range in major direction can reach 15% while that in minor direction can reach 25%. The variogram is very sensitive and the volumes calculated with different models have big difference. The more developed the sand is, the less different the sand volume is. The space varying variogram, improved from normal variogram, is put forward with the varing variogram in planar view. The reliability of variogram could be improved by application of space varying variogram.