The production of associated petroleum gas in the Russian Federation is the most important component of the country's energy supply. Natural gas consumption is increasing annually, both in Russia and in other countries. For example, gas consumption in Europe in the first quarter of 2018 has reached its peak level for five years - 194.3 billion m3 [1]. The increase in exports of Russian natural gas to Germany by 12.4%, Austria - by 62.5%, to the Netherlands - by 80.5%, Croatia - by 2.5 times, China - by 36% is observed. It is a strategic task for oil and gas companies to account for the production of associated gas, because there is a discrepancy between the production of gas and the volume of the combusted part of the gas, which is primarily due to the lack of effective technologies for measuring the amount of gas, including gas-oil ratio. It is necessary to measure both the free gas phase released from the oil under the pressure at the oil sampling point and the residual amount of dissolved gas in the oil, as well.

The most appropriate and effective way to measure the total gas oil ratio is to measure it with portable devices. According to the Ruling Document (RD) [2], the measurement of the GOR at the wells must be carried out annually when the formation pressure is higher than the saturation pressure. The designers of gas factor measurement units are faced with the task of improving the quality of oil separation from gas under surface conditions and increasing the accuracy of GOR measuring. Measurement of oil, gas and water flow rates at oil production sites can be carried out by immobile or portable automated group metering stations.

A method is known to measure the flow rates of oil, gas and water that is based on determining the filling rates of two successive measuring vessels and their subsequent emptying [3]. The flow rate of the water-oil mixture is determined by the time of filling the vessels, and the flow rate of the gas phase is determined by the speed of emptying the vessels. Water cut of oil or water flow rate is determined by the difference of the reflection coefficient of electromagnetic waves along the height of the liquid column in the cylinder at the moment of its filling. The drawback of this method is that there are dispersed water and gas phases in the form of droplets and bubbles present in a liquid that fills the cylindrical vessel during measurements, which leads to a significant measurement error. In addition, a sufficient amount of dissolved associated gas remains in the oil phase, which does not escape from oil at the operating pressure (usually the pressure of the pressure manifold) and therefore cannot be taken into account in the calculations of the gas content in oil or the gas flow rate.

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