Development of New Gas Viscosity Correlations
- Kadhem Salman Al-Nasser (South Rub Al-Khali Company Ltd) | Muhammad Ali Al-Marhoun (King Fahd U. of Petr. & Min.)
- Document ID
- Society of Petroleum Engineers
- SPE International Production and Operations Conference & Exhibition, 14-16 May, Doha, Qatar
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.2.1 Phase Behavior and PVT Measurements, 7.2.2 Risk Management Systems, 5.5 Reservoir Simulation, 4.6 Natural Gas
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Most of the existing correlations for estimating gas viscosity were developed in mid 60's and 70's of the last century. Limited number of data was used to develop them and their accuracies are questionable. Predicting accurate gas viscosity is extremely important in the oil and gas industry as it has a major impact on reservoir recovery, fluid flow, deliverability, and well storage.
In this study, a new correlation has been introduced. This correlation is simpler, features higher accuracy, and uses fewer coefficients compared with the existing correlations. Its application covers a wider range of gas specific gravity without jeopardizing the accuracy of the correlation. Another model was built using Artificial Neural Networks, ANN in order to compare its results with those obtained from the new correlation.
The existing correlations were studied and analyzed using the same, large set of measured data used for this study. Most of these correlations suffered from high errors and thus were optimized using the linear and non-linear regressions. New set of coefficients for these correlations are recalculated for which the accuracy has significantly improved. In spite of such an improvement, the new correlation and new ANN model outperform the existing correlations.
Many correlations have been proposed for gas viscosity estimation. These methods include Carr, et al., Jossi, et al, which was adapted by Lohernz, Bray and Clark, Dien and Stiel, Lee, et al. and Sutton. Carr, et al. 1 correlation has been very popular for estimating gas viscosity. Lee, et al. correlation has been used widely since mid 80s as it has proven to be more accurate. Each of these correlations will be discussed briefly below. The corresponding viscosity correlations are shown in Appendix A.
1. Carr, et al.1- Dempsey2-Standing3 method
Until recently, this correlation was considered to be the main correlation for estimating gas viscosity in petroleum industry. Carr, et al.1 used their experimental data (and Comings, Mayland, and Egly data) to create a graphical correlation, as function of reduced pressures and temperatures. Results were used to construct cross plots, which were a function of pseudo-reduced pressure, pseudo-reduced temperature and viscosity ratio. The main advantage of this correlation is its simplicity as well as the corrections it has for the existence of non-hydrocarbon gases such as CO2, N2 and H2S.
Carr, et al.1 correlation is reported to have an average of 0.38 absolute error. This correlation is recommended to be used for gases with specific gravity between 0.55 and 1.22 and a temperature range between 100 and 300 ºF.
Dempsey2 (1965) expressed the viscosity ratio for Carr, et al.1 chart µg/ µ1 mathmatical formula as shown in Appendix A.
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