Abstract
The physical and compositional properties of live crude oils strongly affect the strategy of transportation of oil and gas from reservoirs to the stock tank and their storage. The relevant PVT properties of live crude oils like solution gas-oil ratio and oil formation volume factor should be measured preferably in laboratory for different pressures at the process or reservoir temperature. The sampling and PVT analysis include time consuming or expensive procedures and the data obtained are correlated for interpolation or estimation of properties. These properties vary considerably for different classes of crude oils. We obtain experimental data of crude oils properties from the PVT analysis of primary high-pressure separator samples of 260 live paraffinic-naphthenic crude oils from forty-four Brazilian oil wells. The solution gas-oil ratio and oil formation volume factor were obtained within experimental uncertainties of 5.79% and 1.00%, respectively. We have compared the results with the estimates of several cubic equations of state as well as with widely used literature correlations. The best equation of state estimate solution gas-oil ratio with average absolute percent relative error (AARE) of 10.36%, better than the empirical correlations in the literature using measured temperature, pressure and composition, the empirical correlation for solution gas-oil ratio with parameters estimated from the experimental data shows an AARE of 10.77%. The equations of state and literature correlations estimate the oil formation volume factor with an AARE about 2%, which is lower than the needed accuracy. The measured oil formation volume factors are correlated with an average absolute percent relative error of 1.18%, with a proposed correlation using readily measured liquid densities and solution gas-oil ratio. We can estimate the solution gas-oil ratio by Peng-Robinson equation of state and oil formation volume factor by proposed correlation to the needed accuracy for live paraffinic-naphthenic crude oils under separator conditions from composition, temperature and densities of gas and oil.
Highlights
The oil and gas are separated from reservoir fluids in one or more stages in upstream production platforms, usually at higher than atmospheric pressures to ensure maximum recovery of oil
Used literature correlations for solution gas-oil ratio and oil formation volume factor were evaluated in their ability to represent the experimental data and the estimated values showed large deviations
We measured composition of the samples to apply equations of states of Peng-Robinson and SoaveRedlich-Kwong. These equations were evaluated for their ability to calculate the values of solution gas-oil ratio and oil formation volume factor
Summary
The oil and gas are separated from reservoir fluids in one or more stages in upstream production platforms, usually at higher than atmospheric pressures to ensure maximum recovery of oil. During the flow of live crude oils in the pumping system or in the storage tanks, the temperatures and the pressure can vary. During the economic production period, the pressure, temperature and composition of oil vary considerably. These changes cause considerable variation of properties of the live crude oils produced in the primary separator. The changing properties of live crude oils should preferably be measured experimentally at various temperatures and pressures in the laboratory by a PVT analysis, which includes procedures which are expensive and time consuming. The experimental measurements can be used to evaluate the reliability of correlations proposed in the literature to estimate these properties
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