Abstract: 3D variation function is the most important parameter showing reservoir heterogeneity. But, this basic factor in today's reservoir stochastic modeling tends to being ignored. In light of vertical distribution characteristic of reservoir petrophysical property, the geologic factors affecting the 3D variation function such as singular value, hybrid distribution and drifting are systematically analyzed. The corresponding measures and methods for eliminating these factors are outlined, and the work flow for solving the 3D variation function is proposed in this paper.

Key words: variation function, drifting, hybrid/mixed distribution, singular value, outlier