Although upscaling has been extensively investigated, a quantitative relationship between the multi-million block geological model and the upscaled flow model is likely to be lost during the history match process, primarily due to parameter modification on an upscaled model. In this paper, we propose a new history match procedure combined with an innovative faster upscaling technique.
In the proposed procedure, after each history run, parameter modification for the next run was done on the detailed geological model in close collaboration with geologist. This loop was made possible with a new faster upscaling technique, distinct against the existing method, by adopting empirical correlations of computing upscaled absolute and relative permeabilities. A capillary-limit upscaling technique was applied for the case study, since a target reservoir is capillary dominant.
In the case study, history match was conducted on a sector of an oil-wet carbonate reservoir under waterflooding for 20 years. In each modification, the revised geological model of three million blocks was upscaled to a flow model of 60 thousand blocks in a process independent manner with a scale-up factor of 50. The CPU speed-up factor was approximately 200: 10 days for the detailed model with massive parallel computing and an hour for the upscaled model with a personal computer.
Even with such significant CPU time reduction, it was confirmed that the upscaled model still maintained the simulation quality of the detailed geological model.