Abstract
The surface tension that exists between hydrocarbon and water systems is an important property within the petroleum industry. Uses of this property range from quantifying its effects on capillary pressure which governs the vertical saturation distribution of hydrocarbons in a reservoir to determining liquid droplet size for multiphase flow calculations. A general correlation for estimating water-hydrocarbon surface tension has been developed. Prior generalized methods presented in the literature were found to be in error for gases other than methane and did not adequately characterize the change in surface tension with temperature. A large database consisting of 1902 data points was created as part of the development of the correlation. Pure hydrocarbon component surface tension measurements against pure water provide the basis for this database. Data ranging from methane through hexadecane as well as benzene and toluene were included in the main database. Pure water data at vapor pressure equilibrium was also included in the analysis to ensure that changes in surface tension with temperature were modeled accurately. In addition, natural gas, natural gas-carbon dioxide and natural gas-nitrogen mixtures with pure water were tested with the new correlation to ensure realistic scenarios could be accurately modeled. Pressure data covered the range from 14.7 to 43,526 psia while temperature ranged 33–500 °F which ensures that both conventional and HPHT conditions can be modeled. Real hydrocarbon-water systems usually contain dissolved salts in the water; therefore, a salinity correction must be applied to account for the increase in surface tension. Available data from the literature was examined and a suitable correction is proposed. This paper presents the analysis of an exhaustive database and proposes a new correlation to model water-hydrocarbon surface tension with significantly higher accuracy.
