Gigacell grids: indulgence or necessity

Upscaling techniques developed in the late 1980s continue to form the basis of including detailed geological data in flow simulation models. While these techniques are theoretically robust, in practice the process of upscaling has variable success and the concept of replacing a complex and detailed geological model with an array of effective properties is considered to be a source of error in the construction of simulation models. The default ratio between the geological grid and the simulation grid in popular geological modelling programs is eight fine cells to one coarse cell. Examination of the number of samples required to estimate the mean value of a population suggest that this ratio should be much higher, and that more accurate upscaling results would be obtained if there were 1,000 fine cells in each coarse cell. This suggests that a simulation grid of 500,000 cells should have a corresponding geological grid with 500 million cells to improve the accuracy of the computation of effective properties. This is beyond the capabilities of the present generation of commercial geological modelling software used in the petroleum industry. This paper discusses the creation of gigacell grids, and the ease of construction and difficulties in population using existing geostatistical algorithms.