Methodological foundations for calculating the amount of gas dissolved in formation water

UDK: 622.276.346.2
DOI: 10.24887/0028-2448-2022-6-92-94
Key words: crude oil production, reservoir water, wet oil, gas reserves
Authors: N.A. Ovechkina (Tyumen Branch of SurgutNIPIneft, Surgutneftegas PJSC, RF, Tyumen), M.A. Kasperovich (Tyumen Branch of SurgutNIPIneft, Surgutneftegas PJSC, RF, Tyumen), O.V. Fominyh (Industrial University of Tyumen, RF, Tyumen)

At high-water-cut objects that are at a late stage of development, not only an increase in the water cut of well production is often observed, but also a simultaneous increase in the gas factor of oil to values exceeding those accepted in the calculation of reserves. The increase in the gas factor is due to the presence of gas dissolved in produced water. The volume of produced gas dissolved in water can often be comparable to or greater than the volume of gas dissolved in oil, and can significantly affect the discrepancy between the approved and actual gas production figures. Despite the existing scientific work in this direction, the possibility of forecasting and accounting for the volumes of such gas is not reflected in the regulatory documents. In this regard, an urgent task is to develop a methodology that allows to calculate the volumes of gas dissolved in water based on measured field data. When performing the task, it is important to justify the assumption about the possible impact of gas dissolved in produced water on the total gas production.

The article presents an algorithm for calculating the gas content of formation water to account for associated gas, based on the known dependences of the solubility of the main gas components (methane and nitrogen) with amendments that take into account the salinity of produced water, the solubility of methane in reservoir conditions, as well as phase equilibrium constants that depend on the composition and parameters of the phases. To test the developed algorithm, a series of calculations was carried out. Comparison of the results of calculations with the data of laboratory studies of mass transfer between gas-saturated oil and saline water and field measurements of the gas factor of production of high-water cut wells is carried out.

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