## Hydrocarbon Composition

The petroleum fluids from reservoirs normally are multiphase and multicomponent mixtures, primarily consisting of hydrocarbons, which can be classified into the following three groups:
Physical Properties of Main Petroleum Components
Typical Compositon of a Gas Condensate
• Paraffins;
• Naphthenes;
• Aromatics.

In addition to hydrocarbons, water (H2O), nitrogen (N2), carbon dioxide (CO2), hydrogen sulfide (H2S), salts, and solids are often found in petroleum mixtures.

An increase in the carbon number of the component formula. If the carbon number of a component is less than 5, the component is in the gas phase at atmospheric pressure. When the mixture contains larger molecules, it is a liquid at normal temperatures and pressures. A typical petroleum fluid contains thousands of different chemical compounds, and trying to separate it into different chemical homogeneous compounds is impractical.

## Equation of State

For oil and gas mixtures, the phase behavior and physical properties such as densities, viscosities, and enthalpies are uniquely determined by the state of the system. The equations of state (EOS) for petroleum mixtures are mathematical relations between volume, pressure, temperature, and composition, which are used for describing the system state and transitions between states. Most thermodynamic and transport properties in engineering analyses are derived from the EOS. Since 1873, when the first EOS for representation of real systems was developed by the van der Waals, hundreds of different EOSs have been proposed and they are distinguished by Leland into four families:

1. van der Waals family;

2. Benedict-Webb-Rubin family;

3. Reference-fluid equations;

4. Augmented-rigid-body equations.

The cubic equations of the van der Waals family are widely used in the oil and gas industry for engineering calculations because of their simplicity and relative accuracy for describing multiphase mixtures. The simple cubic equations of state, Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR), are used in flow assurance software (e.g., PIPESIM). They require limited pure component data and are robust and efficient, and usually give broadly similar results.

The SRK Equation

The SRK Equation

PR Equation

PR Equation

## Hydrocarbon Properties

Oil and gas are very complex fluids composed of hydrocarbon compounds that exist in petroleum in a wide variety of combinations. Physical properties change with the component composition, pressure, and temperature. No two oils have the same physical properties. In considering hydrocarbon flow in pipes, the most important physical properties are density and viscosity.

### Density

Dead oil is defined as oil without gas in solution. Its specific gravity go is defined as the ratio of the oil density and the water density at the same temperature and pressure:
Water density at the same temperature and pressure
Oil density calculated

### Viscosity

The dynamic viscosity of a fluid is a measure of the resistance to flowexerted by a fluid. The viscosity of Newtonian fluids is a function of temperature and pressure. If the viscosity of a fluid varies with the thermal or time history, the fluid is called non-Newtonian. Most of the hydrocarbon fluids are Newtonian fluid, but in some cases, the fluid in the flowline should be considered to be non-Newtonian. The viscosity of oil decreases with increasing temperature, while the viscosity of gas increases with increasing temperature. The general relations can be expressed as follows for liquids:

The viscosity of crude oil with dissolved gases is an important parameter for the calculation of pressure loss for hydrocarbon flow in pipeline. Pressure drops of high viscous fluid along the pipeline segment may significantly impact deliverability of products. The oil viscosity should be determined in the laboratory for the required pressure and temperature ranges. Many empirical correlations are available in the literature that can be used to calculate the oil viscosity based on the system parameters such as temperature, pressure, and oil and gas gravities when no measured viscosity data are available.

To minimize pressure drop along the pipeline for viscous crude oils, it is beneficial to insulate the pipeline so it can retain a high temperature. The flow resistance is less because the oil viscosity is lower at higher temperatures. The selection of insulation is dependent on cost and operability issues. For most developed fields insulation may not be important. However, for heavy oil, high-pressure drops due to viscosity in the connecting pipeline between the subsea location and the receiving platform, insulation may have a key role to play.

## References

[1] R.C. Reid, J.M. Prausnitz, T.K. Sherwood, The Properties of Gases and Liquids, third ed., McGraw-Hill, New York, 1977.

[2] K.S. Pedersen, A. Fredenslund, P. Thomassen, Properties of Oils and Natural Gases, Gulf Publishing Company (1989).

[3] T.W. Leland, Phase Equilibria, Fluid, Properties in the Chemical Industry, DECHEMA, Frankfurt/Main, 1980. 283–333.

[4] G. Soave, Equilibrium Constants from a Modified Redilich-Kwong Equation of State, Chem. Eng. Sci vol. 27 (1972) 1197–1203.

[5] D.Y. Peng, D.B. Robinson, A New Two-Constant Equation of State, Ind. Eng. Chem. Fundam. vol. 15 (1976) 59–64.

[6] G.A. Gregory, Viscosity of Heavy Oil/Condensate Blends, Technical Note, No. 6, Neotechnology Consultants Ltd, Calgary, Canada, 1985.

[7] G.A. Gregory, Pipeline Calculations for Foaming Crude Oils and Crude Oil-Water Emulsions, Technical Note No. 11, Neotechnology Consultants Ltd, Calgary, Canada, 1990.

[8] W. Woelflin, The Viscosity of Crude Oil Emulsions, in Drill and Production Practice,, American Petroleum Institute vol. 148 (1942) p247.

[9] E. Guth, R. Simha, Untersuchungen u¨ber die Viskosita¨t von Suspensionen und Lo¨sungen. 3. U¨ ber die Viskosita¨t von Kugelsuspensionen, Kolloid-Zeitschrift vol. 74 (1936) 266–275.

[10] H.V. Smith, K.E. Arnold, Crude Oil Emulsions, in Petroleum Engineering Handbook, in: H.B. Bradley (Ed.), third ed., Society of Petroleum Engineers, Richardson, Texas, 1987.

[11] C.H. Whitson, M.R. Brule, Phase Behavior, Monograph 20, Henry, L. Doherty Series, Society of Petroleum Engineers, Richardson, Texas, (2000).

[12] L.N. Mohinder (Ed.), Piping Handbook, seventh, ed., McGraw-Hill, New York, 1999.

[13] L.F. Moody, Friction Factors for Pipe Flow, Trans, ASME vol. 66 (1944) 671–678.

[14] B.E. Larock, R.W. Jeppson, G.Z.Watters, Hydraulics of Pipeline Systems, CRC Press, Boca Raton, Florida, 1999.

[15] Crane Company, Flow of Fluids through Valves, Fittings and Pipe, Technical Paper No. 410, 25th printing, (1991).

[16] J.P. Brill, H. Mukherjee, Multiphase Flow in Wells, Monograph vol. 17(1999), L. Henry, Doherty Series, Society of Petroleum Engineers, Richardson, Texas.

[17] H.D. Beggs, J.P. Brill, A Study of Two Phase Flow in Inclined Pipes,, Journal of Petroleum Technology vol. 25 (No. 5) (1973) 607–617.

[18] Y.M. Taitel, D. Barnea, A.E. Dukler, Modeling Flow Pattern Transitions for Steady Upward Gas-Liquid Flow in Vertical Tubes, AIChE Journal vol. 26 (1980) 245.

[19] PIPESIM Course, Information on Flow Correlations used within PIPESIM, (1997). 398 Y. Bai and Q. Bai

[20] H. Duns, N.C.J. Ros, Vertical Flow of Gas and Liquid Mixtures in Wells, Proc. 6th World Petroleum Congress, Section II, Paper 22-106, Frankfurt, 1963.

[21] J. Qrkifizewski, Predicting Two-Phase Pressure Drops in Vertical Pipes, Journal of Petroleum Technology (1967) 829–838.

[22] A.R. Hagedom, K.E. Brown, Experimental Study of Pressure Gradients Occurring During Continuous Two-Phase Flow in Small-Diameter Vertical Conduits, Journal of Petroleum Technology (1965) 475–484.

[23] H. Mukherjce, J.P. Brill, Liquid Holdup Correlations for Inclined Two-Phase Flow, Journal of Petroleum Technology (1983) 1003–1008.

[24] K.L. Aziz, G.W. Govier, M. Fogarasi, Pressure Drop in Wells Producing Oil and Gas, Journal of Canadian Petroleum Technology vol. 11 (1972) 38–48.

[25] K.H. Beniksen, D. Malnes, R. Moe, S. Nuland, The Dynamic Two-Fluid Model OLGA: Theory and Application, SPE Production Engineering 6 (1991) 171–180. SPE 19451.

[26] A. Ansari, N.D. Sylvester, O. Shoham, J.P. Brill, A Comprehensive Mechanistic Model for Upward Two-Phase Flow in Wellbores, SPE 20630, SPE Annual Technical Conference, 1990.

[27] A.C. Baker, K. Nielsen, A. Gabb, Pressure Loss, Liquid-holdup Calculations Developed, Oil & Gas Journal vol. 86 (No 11) (1988) 55–59.

[28] O. Flanigan, Effect of Uphill Flow on Pressure Drop in Design of Two-Phase Gathering Systems, Oil & Gas Journal vol. 56 (1958) 132–141.

[29] E.A. Dukler, et al., Gas-Liquid Flow in Pipelines, I. Research Results, AGA-API Project NX-28 (1969).

[30] R.V.A. Oliemana, Two-Phase Flow in Gas-Transmission Pipeline, ASME paper 76- Pet-25, presented at Petroleum Division ASME Meeting, Mexico City, (1976).

[31] W.G. Gray, Vertical Flow Correlation Gas Wells API Manual 14BM (1978).

[32] J.J. Xiao, O. Shoham, J.P. Brill, A Comprehensive Mechanistic Model for Two-Phase Flow in Pipelines, SPE, (1990). SPE 20631.

[33] S.F. Fayed, L. Otten, Comparing Measured with Calculated Multiphase Flow Pressure Drop, Oil & Gas Journal vol. 6 (1983) 136–144.

[34] Feesa Ltd, Hydrodynamic Slug Size in Multiphase Flowlines, retrieved from http:// www. feesa.net/flowassurance.(2003).

[35] Scandpower, OLGA 2000, OLGA School, Level I, II.

[36] Deepstar, Flow Assurance Design Guideline, Deepstar IV Project, DSIV CTR 4203b–1, (2001).

[37] J.C. Wu, Benefits of Dynamic Simulation of Piping and Pipelines, Paragon Technotes (2001).

[38] G.A. Gregory, Erosional Velocity Limitations for Oil and Gas Wells, Technical Note No. 5, Neotechnology Consultants Ltd, Calgary, Canada, 1991.

[39] American Petroleum Institute, Recommended Practice for Design and Installation of Offshore Platform Piping System, fifth edition,, API RP 14E, 1991.

[40] M.M. Salama, E.S. Venkatesh, Evaluation of API RP 14E Erosional Velocity Limitations for Offshore Gas Wells, OTC 4485 (1983). Hydraulics 399