The article summarizes the analysis of the current state of development of an oil-gas-condensate field in Eastern Siberia. It is revealed a sharp decrease in the productivity index of horizontal wells when the water cut changes from 0 to 10–15%. This fact significantly affects the achievement of designed technological indicators of well operation. Based on the analysis, the influence of the characteristics and structure of the two-phase flow in the reservoir in the the Lower Neokomian subformation on the decrease in the productivity index is established. Characteristic geological and geophysical features for hydrophobic and hydrophilic rocks are identified and described. A comprehensive study of the movement of individual phases in a multi-phase flow is based on the Buckley – Leverett theory, we used the equation for determining the proportion of water in the total fluid flow at any point in a porous medium. The paper investigates the nature of the relationship between the mobility of a two-phase flow and the productivity index of wells during the operation of a hydrophobic reservoir, and also interprets the results of studying the dependence of the productivity factor on water cut. The reason for the sharp decrease in the productivity index of wells in the hydrophobic reservoir of the studied oil-gas-condensate field with a low initial water cut is revealed. It is concluded that for the geological and physical conditions of the reservoir in the Lower Neokomian subformation, the change in the value of the productivity index occurs according to hyperbole and with a water cut of well production of 5-8%, its multiple decrease is noted - by 2-5 times. The established pattern of changes in the productivity factor of wells at the initial stages of watering must be taken into account when planning geological and technical measures when developing a hydrophobic reservoir.
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