Peculiarities of Lihology and Petrophysical Parameters Calculation and Transfer from Epilogs to 3D Geomodel

Abstract

Abstract The method of averaging epilog parameters into the cell of 3D grid depends on the type of parameters and vertical cell size. The objective is to improve methods of calculating and transferring epilogs into the 3D grid of geological model. The paper presents the typical mistakes made by designers while reservoir parameters transfer into the 3D grid of geological and hydrodynamic models. The method of pseudo anisotropy factor (Kv / Kh) calculation from well epilogs had been proposed. The model loses connectivity of the reservoir and understated HCIP when it cells are resulting to non-reservoir ones due to sufficiently high cutoff value of net-to-gross (up to 0.5) for the lithology parameter (reservoir / non-reservoir). To compensate for such imbalance reservoir engineers often neglect the NTG value for reservoir cells, calculating epilog parameters only for the reservoir intervals. Reducing the value for the NTG cutoff down to 0.1-0.2 and the introduction of NTG values for all reservoir cells allows more accurately reproduce the hydrodynamic connectivity of the model and the HCIP distribution. It is shown that if the value of permeability in the reservoir cell of 3D grid calculate through the mean porosity for all epilog intervals of the cell, then the permeability value will correspond to the geometric mean, and will characterize the vertical permeability. To obtain a correct value for the lateral permeability of the cell it is necessary to calculate it as an arithmetic mean value for all reservoir intervals of the epilog within this cell. The ratio of vertical and lateral permeability will give us the value for the pseudo anisotropy of the cell. Guidelines for calculation and transfer of the epilogs into 3D grid shown in the work will result in the correct initial distribution of the lateral and vertical permeability in the geological and hydrodynamic models, differentiated values for the pseudo anisotropy factors of cells. For the cases of geological models construction with hydrodynamic grid dimensions the upscaling is performed while transferring well epilogs into the 3D geological grid. The proposed method allows more correct averaging for the initial permeability distribution and calculate the vertical anisotropy for the reservoir cells as a function of their heterogeneity.