Probabilistic evaluation of the permeability of the rocks of the elementary cell of a geological model

Abstract

The article proposes a new method for calculating the permeability of a geological model cell using probabilistic methods. It is proposed as an alternative to the generally accepted method, which is based on the use of empirical dependencies between porosity and permeability based on the results of laboratory core tests. The proposed method allows us to calculate the dependences of the probabilities of exceeding certain permeability values on porosity. These are of interest for studying the geological structure of oil and gas facilities in the process of their modeling. In this work, the boundary values of filtration properties corresponding to the boundaries of reservoir classes in the classification proposed by A. A. Khanin in 1969 were used. The article discusses the problems arising from the integration of different-scale levels. One of their solutions can be obtained by using the Monte Carlo method. In particular, its use helped to simulate the reservoir properties of rocks in a virtual cell of a geological model based on analyses of the results of previous studies of core samples in laboratory conditions. The approximation of the probabilities of exceeding the corresponding values of permeability from porosity allows us to calculate histograms of this parameter for each cell of the model. To do this, it is necessary to determine the differences in the probability functions that are used for neighboring permeability thresholds. In turn, this makes it possible to perform a differentiable assessment of hydrocarbon reserves for the corresponding reservoir classes in terms of permeability. The article discusses a methodology that allows you to perform all calculations in an automated mode. The text of the article provides the necessary description of the program for calculating the probabilities of exceeding the permeability thresholds, as well as a schematic diagram reflecting the main provisions of its work. The article substantiates the expediency of not using porosity thresholds for reservoir identification. Instead, permeability histograms are calculated for each cell. This methodological scheme makes it possible to calculate reserves associated with rocks of various permeability classes in an automatic mode. Keywords: bottomhole formation zone; asphalt-resin-paraffin deposits; nitrite composition; surfactants; enhanced oil recovery.