On the Viscosity of Natural Gases from Qatari North Field Reservoir Mert Atilhan,* ,† Santiago Aparicio,* ,‡ Gustavo A. Iglesias-Silva, § Mahmoud El-Halwagi, | and Kenneth R. Hall | Department of Chemical Engineering, Qatar University, 2713 Doha, Qatar, Department of Chemistry, University of Burgos, 09001 Burgos, Spain, Departamento Ingenierı ´a Quı ´mica, Instituto Tecnolo ´gico de Celaya, Celaya, Guanajuato, Mexico, and Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843 New viscosity measurements of three natural gas-like mixtures with compositions resembling those of the Qatari North Field reservoir are reported in this work. The viscosity measurements were performed with an electromagnetic piston viscometer for temperatures from (250 to 450) K and pressure between (10 and 65) MPa. The apparatus was calibrated by use of nitrogen and propane as viscosity reference data. Uncertainties of reported data are ( 2.5 % for pressure less than 30 MPa and ( 4 % for higher pressures. The predictive ability of several models was analyzed in relation to the experimental reported viscosity data, leading to large deviations from the reported measurements. The effects of mixtures’ composition on viscosity were also studied. Introduction The total world production of natural gas is expected to increase from the 3.107 · 10 12 m 3 produced in 2008 to 4.370 · 10 12 m 3 in 2035, according to the most reasonable scenarios, and thus, a 1.4 % annual average percent change would be required. 1 The economic importance of natural gas may be inferred by considering that 39 % and 33 % of the world production is used for industrial purposes and for electricity generation, respectively. 1 Moreover, when carbon dioxide emissions from fossil fuel combustion are considered, it is clear that natural gas should be considered as a cleaner fuel in comparison with oil and coal. 2 The probed world total natural gas reserves are estimated to be 185.8 · 10 12 m 3 in 2010, which is a remarkable increment of 9.956 · 10 12 m 3 when compared with 2009 data. 3 The analysis of probed reserves by country shows that Qatar, with 25.28 · 10 12 m 3 probed, has the world’s third largest reservoirs, and thus, Qatar holds almost 14 % of total world natural gas. 3 In 2008, Qatar produced 75.9 · 10 9 m 3 of natural gas, 1 which is more than 5 times the amount produced in 1995; nevertheless, this quantity will increase remarkably in the next years. 1 The majority of Qatar’s natural gas is located in the massive offshore North Field, the world’s largest nonassociated natural gas field. The plans to expand natural gas production from North Field, to meet the expected increase in regional demand and to supply markets outside the region, would allow North Field to produce 205.32 · 10 9 m 3 · a -1 in 2012. 4 Increasing Qatar’s natural gas production will lead to large-scale projects such as new liquefied natural gas (LNG) infrastructure (Qatar is the first world LNG exporter), natural gas exports through the Dolphin pipeline, several large-scale gas-to-liquids (GTL) projects, and the promotion of downstream industries that utilize natural gas as feedstock. 5 The increasing worldwide demand for natural gas is leading to the need for developing reliable and accurate reservoir characterization and simulation. The upstream gas industry is also being faced with increasing needs for precision in the monitoring of gas supplies. Therefore, for optimal production, processing, transportation, and usage of natural gas, accurate and reliable knowledge of the natural gas viscosity, along with other thermophysical properties, is a prerequisite. The effect of gas viscosity estimation errors on the gas recovery from a simulated high pressure-high temperature (HPHT) reservoir was studied by Davani et al. 6 and Denney, 7 using numerical reservoir simulation methods, showing that a - 10 % error in gas viscosity can produce a relative 8.22 % error in estimated cumulative gas production, and a + 10 % error can lead to a relative 5.5 % error in cumulative production. Therefore, accuracy on viscosity data should have a large economical impact. The wide range of possible natural gas mixtures, depending basically on the origin, age, and depth of the reservoir, 8 and of conditions of interest, especially considering the HPHT conditions found in many new reservoirs that can be explored with current technologies, 9 precludes obtaining the relevant data by experimental studies on an exclusive basis. Moreover, to obtain accurate measurements of gas viscosity, especially for HPHT conditions, is very difficult, from a experimental viewpoint, and expensive. 6,10 Therefore, the analysis of published viscosity data found in the open literature shows that it is very limited in terms of both experimental conditions and quantity (see Atilhan et al. 11 and references therein), and in some cases their accuracy is unknown. Thus, the common practice in the natural gas industry is to estimate viscosity from available correlations and predictive methods that are based on available laboratory data. 12-14 Nevertheless, the predictive methods commonly applied in the industry have a reduced range of applicability, both in pressure-temperature conditions and mixtures’ composition, and thus their application for HPHT conditions or for mixtures not previously tested may be doubtful. 7,11,15 Therefore, the available viscosity models do not satisfy the current industrial requirements for flow assurance and reliable reservoir characterizations. The development of accurate and reliable natural gas viscosity models, or testing of * Corresponding authors. E-mail: mert.atilhan@qu.edu.qa (M.A.) or sapar@ ubu.es (S.A.). † Qatar University. ‡ University of Burgos. § Instituto Tecnolo ´gico de Celaya. | Texas A&M University. J. Chem. Eng. Data 2010, 55, 5117–5123 5117 10.1021/je100673w  2010 American Chemical Society Published on Web 09/14/2010