ESTIMATION OF RESIDUAL WATER SATURATION IN 3D GEOLOGICAL MODELING

This article discusses a new method of determining distributional patterns of residual water saturation in reservoirs during digital geological modeling. This is important for the construction of an oil saturation cube and prediction of character of stimulation of a hydrocarbon-bearing formation. Currently, construction of oil saturation cubes uses interpolation of borehole data. The reservoir properties of formations, which have influence on the nature of rock saturation, are neglected in this case. Considering essential scatter in the values of the study parameter and the comparatively large dimensions of the model cells, it is suggested to calculate histograms of residual water saturation coefficients. First, from the core testing data, the probability of non-exceedance of a certain critical water saturation value (80, 60, 40, 20) is calculated as function of porosity. For adapting the resultant dependences to larger objects, the unit cells are represented as sets of virtual rocks, with the sizes comparable with the sizes of core samples; the random number generator gives these rocks the values of reservoir properties such that the initial average values of porosity of the cells are preserved. For each type of conventional rock, the probability of nonexceedance of critical residual water saturation is calculated and the average values of the parameter are determined per cells. The relations between the probability of non-exceedance of critical water saturation and the porosity are approximated. Then, percentages of rocks within certain ranges of residual water saturation in a cell are determined. For the cube construction, the oil saturation index in an all-oil zone will be equal to the difference between one and residual water saturation, and will also depend on the height of rock occurrence above the water-oil contact in a water-and-oil zone.