Prediction of filtration and capacitive properties and oil saturation characteristics of complex structure carbonate reservoirs (on the example of the Northwestern part of DDB)

Abstract

The world achievements of the study of carbonate reservoir rocks with secondary voids have been analyzed. An integrated approach to the study of this type of reservoir has been demonstrated on the example of reservoir rocks of the Visean strata of the South-Berestivske field in the North-Western part of the Dnipro-Donets Basin. The purpose of this article is to predict the reservoir filtration-capacitive properties, as well as oil saturation characte-ristics of complex carbonate reservoir rocks using well logging data. To solve this problem, an integrat-ed approach is used. It includes the methods of porosities balance and functional transformations (normalization) of the electrical and radioactive well logging curves (lateral logging - neutron gamma ray logging, impulse neu-tron-neutron logging - neutron gamma ray logging). As a result, the authors have identified intervals in the Visean carbonate deposits with cavernous voids and cracks. Each individual geophysical method is influenced by the structure of the void space. Due to this, when calculating the porosity coefficient for different probes, the au-thors identify intervals represented by carbonate deposits, mainly of the porous-cavernous type. However, there is an interval of 4287.6-4289.6 m of porous-cavernous-fractured type. It is established that in the selected layers the coefficients of different types of porosity are: secondary - 2.5-6%, cavernous - 1.7-5% and fracture -0.2%. The thickness of pro-ductive sediments varies within 0.8 - 2.4 m (the average value is 2 m). The authors also substantiated the choice of parameters when calculating the saturation coefficient in complex structural reservoirs. Moreover, it is noted that the reservoir properties are provided by the presence of secondary voids, namely the cavities through which the fluid is filtered, and the rock matrix is compacted, poor-porous and low-permeable.