A Novel Simplification for the Prediction of Natural Gas Compressibility Factor

The need for a simpler, effective and less expensive predictive tool for the estimation of natural gas compressibility factor cannot be exaggerated. An accurate prediction of gas compressibility factor is essential because it plays a definitive role in evaluating gas reservoir properties used in the estimation of gas reserves, custody transfer and design of surface equipment. In this present work, a novel explicit correlation and a highly sophisticated computer program were developed to accurately predict natural gas deviation factor. The research also aims to effectively capture the relationship between Pseudo-reduced temperature and pressure in relations to the Z-factor. In this study, 3972 digitized data points extracted from Standing and Katz’s Chart were regressed and analyzed using Microsoft Excel Spreadsheet, the extraction of this data was done using WebPlotDigitizer developed by Ankit Rohatgi of GitHub, Pacifica, CA, USA. The correlation was developed as a function of Pseudo-reduced temperature and pressure with tuned parameters distributed across 1.05 ≤ Tpr ≤ 3.0 and 0 < Ppr ≤ 8.0. Subsequently, the input (Tpr and Ppr values) of the feed data was used to validate the correlation and compare it with other known and published correlations. Statistical analysis of the results showed that a 99.8% agreement exists between the predicted and actual compressibility factors for the various test scenarios and case studies involving both sweet and sour gases. Also, the correlation was observed to outperform other models. Finally, the results were observed to perfectly mimic the Standing and Katz charts with an overall correlation coefficient of 99.76% and an adjusted R2 of 99.75%. The proposed correlation was subsequently used to develop a software using JavaScript. Undoubtedly, the proposed correlation and software are suitable for rapid and accurate simplification and prediction of natural gas compressibility factor.

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Compressibility Factors for Lean Natural Gas-Carbon Dioxide Mixtures at High Pressure

Society of Petroleum Engineers Journal ◽

10.2118/1590-pa ◽

1967 ◽

Vol 7 (01) ◽

pp. 80-86 ◽

Cited By ~ 19

Author(s):

Thomas S. Buxton ◽

John M. Campbell

Keyword(s):

Carbon Dioxide ◽

Natural Gas ◽

Compressibility Factor ◽

Corresponding States ◽

Bulk Property ◽

Acentric Factor ◽

Reliable Determination ◽

Temperature And Pressure ◽

Compressibility Factors ◽

Reduced Temperature

Abstract The most widely used methods of predicting the volumetric properties of gas are based on the principle of corresponding states, which asserts that the compressibility factor is a universal function of reduced temperature and pressure. Previous studies have shown that the acentric factor, as proposed by Pitzer,1 is an important addition to reduced pressure and reduced temperature as factors affecting the compressibility factor. Results of this study indicate that, if the pseudocritical temperature and pressure used to determine the reduced conditions are adequately predicted, characterization of natural gas-carbon dioxide mixtures with the acentric factor will allow reliable determination of the compressibility factor. Comparisons of predicted and experimental compressibility factors have shown that the pseudocritical constant rules of Stewart, Burkhardt and Voo2 are satisfactory for hydrocarbon mixtures. However, these rules fail to predict the pseduocritical constants for hydrocarbon-carbon dioxide mixtures. Based on graphically determined pseudocritical temperatures for binary hydrocarbon-carbon dioxide mixtures, a correlation which gives the required correction to the Stewart, Burkhardt and Voo rules was prepared and a compressibility factor prediction technique was proposed. To test the proposed technique; compressibility factors for five mixtures of methane, carbon dioxide and either ethane or propane were experimentally determined at 100, 130 and 160F and pressures up to 7,026 psia. The predicted and experimental compressibility factors for these five mixtures had an average absolute deviation of 0.55 percent. INTRODUCTION Two-parameter generalized correlations based on the principle of corresponding states (PCS) are presently available for reliably predicting the compressibility factor of lean natural gas, i.e., natural gas with low concentrations of hydrocarbons heavier than methane. When these same correlations are used for mixtures of natural gas and carbon dioxide, large deviations between actual and predicted compressibility factors are observed. This study was undertaken to provide a means for accurately predicting the compressibility factor for such mixtures. In the past, two avenues of approach have been employed to extend the applicability of the PCS. The first has been to introduce additional parameters. The second has been to develop combination rules for predicting pseudocritical constants which do not suffer from the limitations of the commonly used molal average constants. In this study, both of these approaches have been considered and employed to arrive at a method for predicting the compressibility factor of mixtures of hydrocarbons and carbon dioxide. SELECTION OF A THIRD PARAMETER Failure of the original PCS to predict the compressibility factor for all pure gases, regardless of their mass, shape or polar moment, has led to the introduction of additional parameters into the PCS. Parameters have been introduced to correct for quantum deviations,3-5 non-spherical or globular shapes6-9 and for polar moments.8-12 In addition to these parameters which are based on some microscopic property and intended to correct for some specific cause of deviation, more general parameters based on some bulk property have also been introduced.1,13-16 To use additional parameters to correct for each of the possible causes of deviation among the individual constituents of a gas mixture would require a rather complex form of the PCS. To maintain the PCS in as simple a form as possible, it is more desirable to have a single third parameter which is based on some bulk property influenced by several of the factors causing deviations.

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Gas compressibility factor explicit correlations for range of pseudo reduced temperature and pressure

Flow Measurement and Instrumentation ◽

10.1016/j.flowmeasinst.2019.05.003 ◽

2019 ◽

Vol 67 ◽

pp. 176-185 ◽

Cited By ~ 3

Author(s):

Kale B. Orodu ◽

Emmanuel E. Okoro ◽

Oluwaseye K. Ijalaye ◽

Oyinkepreye D. Orodu

Keyword(s):

Compressibility Factor ◽

Temperature And Pressure ◽

Gas Compressibility ◽

Reduced Temperature

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A Comprehensive Review of Recent Advances in the Estimation of Natural Gas Compressibility Factor

10.2118/207083-ms ◽

2021 ◽

Author(s):

Oluwasegun Cornelious Omobolanle ◽

Oluwatoyin Olakunle Akinsete

Keyword(s):

Artificial Intelligence ◽

Equation Of State ◽

Compressibility Factor ◽

Operating Conditions ◽

Measurement Equation ◽

Comprehensive Review ◽

Holistic Understanding ◽

Deviation Factor ◽

Gas Compressibility ◽

Limited Accuracy

Abstract Accurate prediction of gas compressibility factor is essential for the evaluation of gas reserves, custody transfer and design of surface equipment. Gas compressibility factor (Z) also known as gas deviation factor can be evaluated by experimental measurement, equation of state and empirical correlation. However, these methods have been known to be expensive, complex and of limited accuracy owing to the varying operating conditions and the presence of non-hydrocarbon components in the gas stream. Recently, newer correlations with extensive application over wider range of operating conditions and crude mixtures have been developed. Also, artificial intelligence is now being deployed in the evaluation of gas compressibility factor. There is therefore a need for a holistic understanding of gas compressibility factor vis-a-vis the cause-effect relations of deviation. This paper presents a critical review of current understanding and recent efforts in the estimation of gas deviation factor.

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An accurate empirical correlation for predicting natural gas compressibility factors

Journal of Natural Gas Chemistry ◽

10.1016/s1003-9953(11)60352-6 ◽

2012 ◽

Vol 21 (2) ◽

pp. 184-188 ◽

Cited By ~ 27

Author(s):

Ehsan Sanjari ◽

Ebrahim Nemati Lay

Keyword(s):

Natural Gas ◽

Empirical Correlation ◽

Compressibility Factors ◽

Gas Compressibility

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Calculation Method of Natural Gas Compressibility Factor and its Application in Pipeline Trade

Volume 1: Design and Construction; Environment; Pipeline Automation and Measurement ◽

10.1115/ipc2014-33258 ◽

2014 ◽

Author(s):

Xiaocui Tian ◽

Xiaokai Xing ◽

Rui Chen ◽

Shubao Pang ◽

Liu Yang

Keyword(s):

Natural Gas ◽

Compressibility Factor ◽

Economic Benefits ◽

Ideal Gas ◽

Operating Conditions ◽

Pipeline System ◽

Natural Gas Pipeline ◽

Gas Volume ◽

Gas Compressibility ◽

Simplified Formula

In the custody transfer metering of natural gas, it’s necessary to transform gas volume from metering state into standard state. Natural gas is non-ideal gas, and its compressibility factor varies with different components, temperature and pressure. So the accuracy of its calculation has direct impact on that of natural gas metering, and then affects the economic benefits of the enterprise [1]. According to related standard of China, in the custody transfer metering of natural gas, the formula stipulated by AGA NO.8 should be adopted to calculate compressibility factor. But the components of natural gas must be monitored at all times when this method is used, and the calculation process is complicated. In practical operation of natural gas trade, compressibility factor changes because of frequent adjustment of pipeline operating conditions. In order to simplify the calculation, simplified formula is applied to calculate compressibility factor generally, but it’s difficult to guarantee the accuracy at the same time. In this paper, the simplified formula, which is used for calculating natural gas compressibility factor of a joint-stock natural gas pipeline of CNPC, is modified with the standard formula stipulated by AGA NO.8. After the modification, an empirical formula of compressibility factor calculation applicable to this pipeline system is proposed, whereby the accuracy of compressibility factor calculation is improved. When the modified one is applied to natural gas trade, the accuracy of metering is improved likewise.

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THE INFLUENCE OF PRESSURE AND TEMPERATURE ON THE COMPRESSIBILITY FACTOR

Romanian Journal of Petroleum & Gas Technology ◽

10.51865/jpgt.2021.02.02 ◽

2021 ◽

Vol 2(73) (2) ◽

pp. 13-21

Author(s):

George Iulian Oprea ◽

◽

Artemis Aidoni ◽

Ioana Cornelia Mitrea ◽

Florinel Dinu ◽

...

Keyword(s):

Natural Gas ◽

Entire Range ◽

Compressibility Factor ◽

Ideal Gas ◽

Calculation Methods ◽

Natural Gases ◽

Canadian Association ◽

Compression And Expansion ◽

Gas Compressibility ◽

Reduced Pressures

The natural gas compressibility factor indicates the compression and expansion characteristics of natural gas under different conditions. It is a thermodynamic property used to take into account the deviation of the behaviour of real natural gases from that of an ideal gas. Compressibility factor, Z, values of natural gases are necessary for most petroleum gas engineering calculations. In this study, a comparison between five different calculation methods is presented to determine this critical parameter for the same natural gas at different conditions (pressure and temperature), using Canadian Association of Petroleum Producers, Azizi, Behbahani and Isazadeh, Dranchuk- Purvis- Robinson, Dranchuk-Abu-Kassem and Standing- Katz methods. The correlations are based on the equation of state are often implicit because they require iteration. Many correlations have been derived to enhance simplicity; however, no correlation has been developed for the entire range of pseudo-reduced pressures and temperatures. Azizi, Behbahani and Isazadeh’s method was found to have the biggest error as a result obtained for T=20° C, and p=20 bar is no longer in the field of applicability.

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