The operation of oil and gas fields in the late stages of development is characterized by a high water cut of the well production. Under these conditions, one of the important tasks is to predict the gas factor and total production volume of associated petroleum gas (APG), taking into account its dissolution in formation water. In this regard, the authors proposed methodological approaches for predicting the volume of production of APG, taking into account gas, both dissolved in oil and gas, and dissolved in formation saline water. A method of phase transformations of formation fluids is proposed, which allows, under given temperature and pressure formation conditions and separation conditions, to estimate the increase in gas content of well fluid and the volume of methane released from 1 m3 of formation saline water under temperature and pressure conditions of separation of well fluids. Phase transformations of formation fluids were modeled on the basis of the Cubic Plus Association type equation of state modified by the authors, which takes into account the effects of association of polar mixture molecules. For the convenience of performing practical calculations, algorithms have been developed that are implemented in software. The technique is approved in two subsidiary of the Rosneft Oil Company on 18 subjects to development of oil fields in Western Siberia and showed good convergence with actual data of operation of objects. Application of a technique allowed to increase the forecasting accuracy of extraction of APG in 2020 on average by 60%. These results promote strategy implementation of the Rosneft Oil Company on carbon management till 2035 on the basis of advance planning of development of the petrochemical and power direction of rational use of APG.
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