ERROR ANALYSIS IN OIL FIELD EMISSION CALCULATION

摘要

Getting correct estimates for volatile organic compounds (VOCs) and greenhouse gases (GHGs) is not only important for emission compliance standards for state and national regulatory authorities but also in designing the capital intensive units for control and economic use of the gases coming out of the field storage tanks. Even a minimal error in calculating the gas oil ratios or Reid vapor pressures can propagate to huge errors in yearly estimates of emissions from production sites and ill designed recovery, storage and transport facilities. This paper studies the difference in gas oil ratios and Reid vapor pressure, measured by emission laboratories and those simulated by computer process simulators. It also addresses slightly about the significance of reporting the gas liberated from produced water tanks along with oil storage tank emissions. In this study various samples of crude oil with different API gravities were taken and flash liberation of those samples was carried out through laboratory procedure and then the results were compared from those obtained from process simulator of the same flash process with the exact same conditions. The results showed a high variation in cases where flash process was done of samples with high separator temperature. To address this, on an experimental basis computer process simulator was modified to account for slow change in temperature by breaking the flash process down to an intermediate temperature and then finally flashing to the base conditions. This could very well be the case in the field due to high fluid levels in the tanks. Results from this method were noted to be closer to the empirical lab method than the earlier method. Therefore a possible explanation for the differences in gas oil ratios or Reid vapor pressure between the two processes was suggested. Finally, the paper also shows the qualitative and quantitative importance of including emissions from produced water tanks, by a comparative analysis of various liberated gas samples from oil storage tanks and produced water tanks.