In order to design appropriate recover storage, transportation and processingsystems to handle crude oils, the engineer requires simple equations that canaccurately predict the oil's physical properties. This paper presents somesuitable equations for viscosity, density and gas solubility which were foundto apply to a wide variety of heavy oils produces in Saskatchewan.
The Beggs and Robinson equation was modified and extended to correlateviscosity. The new equation here accounts for temperature, pressure, CH4 concentration and CO2 concentration. An equationproposed by Mehrotra and Svroek was found to be suitable for gas solubility.For oil density, the Rojas equation was extended to account for temperature andCH4/CO2 concentrations.
Heavy oil in Saskatchewan represents an enormous reserve of energy. Forinstance, if the present known reserves could be totally recovered, there wouldbe enough oil to feed Canada's present consumption rate for the next 40 years.Current recovery techniques include conventional pumping, waterflooding. Steamheating and in-situ combustion. Some work has also been done on other enhancedrecovery techniques such as polymer flooding and CO2injection.
Recovered oil is usually treated to separate water and solid particles and thentransported via pipeline or truck to further upgrading stations. In processes, an engineer estimate and design these processes, an engineer requires simpleequations which will allow him to accurately predict how the crude oil is goingto behave.
In this work, 59 heavy crude oils collected from different producingareas/subareas of Saskatchewan were correlated against a variety of existingequations previously presented in the literature. These correlations wereperformed on three important physical properties: viscosity, gas solubility anddensity. The experimental data for these 59 samples were generated over aperiod of many months by procedures previously described by Jha 1.All the equations presented here use mPa.S for viscosity, Kelvin fortemperature, MPa for pressure, more % for gas concentration, g/cm3for density and STP m3 of gas/m3 of oil forsolubility.
The equations were fit using a non-linear, least squares fitting subroutinecalled ZXSSQ, marketed by IMSL, Houston, Texas. In order to obtain improvedfits and/or to include extra independent parameters in the analysis, literatureequations were frequently modified and extended. Although many equations wereresearched in this work, only the most successful ones will be discussed here.Reference to other correlating equations are described by Quail et al2 elsewhere.
Beggs and Robinson3 presented a completely empirical equation forpredicting crude oil viscosity as a function of API gravity and temperature.Their equation is a double logarithmic form given by:
Equation (1) (Available in full paper)
..in which we have substituted specific gravity (?) for API gravity. Thesubscript " d" on viscosity refers to " dead oil" viscosity. This form ofequation has been used by many investigators when dealing with oil viscosityand indeed we found it to be the most accurate type of equation for Saskatchewan heavy oils.