Isothermal PqT measurements on Qatar’s North Field type synthetic natural gas mixtures using a vibrating-tube densimeter Mert Atilhan a,⇑ , Santiago Aparicio b,⇑ , Ferdi Karadas a,⇑ , Kenneth R. Hall c , Rafael Alcalde b a Department of Chemical Engineering, Qatar University, 2713 Doha, Qatar b Department of Chemistry, University of Burgos, 09001 Burgos, Spain c Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843, USA article info Article history: Received 27 February 2012 Received in revised form 5 April 2012 Accepted 6 April 2012 Available online 17 April 2012 Keywords: Density Natural gas Multicomponent mixtures High pressure Equation of state abstract Pressure–density–temperature (PqT) measurements of five natural gas mixtures that represent Qatar’s North Field natural gas reservoirs were carried out at temperatures from (250 to 450) K and at pressures up to 65 MPa by using a Anton Paar Ò (Graz, Austria) vibrating tube densimeter DMA 512P high-pressure cell. Total 20 isotherms from 250 K by 10 K intervals up to 450 K were measured. Experimental density data were compared with two main industry standard equations of state (EOS) namely AGA8-DC92 EOS and GERG2008 EOS. Comparisons of the experimental data with respect to AGA8-DC92 EOS and GERG2008 EOS resulted in prediction deviation ranges of (0.05 to 0.5)% and (0.25 to 0.5)% respectively. Ó 2012 Published by Elsevier Ltd. 1. Introduction Accurate natural gas density measurements at wide tempera- tures and pressure ranges are necessary in order to establish cost effective and reliable custody transfer across pipelines [1]. Refer- ence equation of states (EOS) is used for predicting natural gas den- sity for these purposes. Most widely used and industry standard equation of states are AGA8-DC92 EOS and GERG2008 EOS [2,3]. Oil and gas industry relies on these EOS and for reservoir fluids and pipeline mixtures frequent calibrations are required in order to observe the EOS prediction adequacy for the changing mixture compositions. Accurate density data is required for flow metering measurements, allowing the measurand from a flow meter, volu- metric flow rate, to be converted to a mass flow rate [4]. In theory, for each new pipeline and reservoir mixture composition, new set of accurate experimental PqT data is required. However, in prac- tice, it is difficult to measure all mixture possibilities and the amount of the published data for multi-component gas mixtures that represents natural gas is scarce. Therefore, accurate experi- mental PqT measurements are required for new fields and new pipeline mixture conditions. By obtaining different sets of accurate experimental data for samples that represents a specific reservoir and specific pipeline conditions, equation of state parameters can be fine-tuned and custody transfer calculations can be made accordingly. Based on 2011 figures, according to Energy Informa- tion Administration (EIA), Qatar’s proven natural gas reserves at its offshore reservoirs called as ‘‘North Field’’ stood at approxi- mately 25.4 trillion cubic meters, that is almost 14.9% of all known natural gas reserves and the 3rd largest in the world behind Russia and Iran [5,6]. The North Field is the largest non-associated natural gas reservoir in the world [7,8]. Oil and mostly natural gas indus- tries have great role in Qatar’s development and majority of the na- tional economic structure relies on the natural gas sales income in the form of liquefied natural gas (LNG). Having stressed the impor- tance of natural reserves for Qatari economy, there has been no published academic research that covers systematical study on Qa- tar’s North Field natural gas mixtures. Our research group has pub- lished recently systematical study on the viscosity behavior of five synthetic natural gas mixtures that represents Qatari North Field reservoir gas after sweetening [9,10]; and in this manuscript we re- port the density measurements of five multi component gas mix- tures obtained via vibrating tube densimeter. 2. Experimental 2.1. Materials Synthetic natural gas sample compositions resemble those of typical sweetened Qatar North Field gas. Five different samples (QNG-S1–QNG-S5) were studied to analyze the effects of mixture 0021-9614/$ - see front matter Ó 2012 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.jct.2012.04.008 ⇑ Corresponding authors. E-mail addresses: mert.atilhan@qu.edu.qa (M. Atilhan), sapar@ubu.es (S. Aparicio). J. Chem. Thermodynamics 53 (2012) 1–8 Contents lists available at SciVerse ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct