(88b) Volume-Translated Cubic Eos and PC-SAFT Density Models and a Free Volume-Based Viscosity Model for Hydrocarbons At Extreme Temperature and Pressure Conditions

This research focuses on providing the petroleum reservoir engineering community with robust models of hydrocarbon density and viscosity at the extreme temperature and pressure conditions (up to 500 ^oF and 35000 psi, respectively) characteristic of ultra-deep reservoirs, such as those associated with the deepwater wells in the Gulf of Mexico.  Our strategy is to base the volume-translated (VT) Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) cubic equations of state and PC-SAFT on an extensive data base of high temperature (40 – 500 ^oF), high pressure (1000 – 40000 psi) density rather than fitting the models to low pressure saturated liquid density data.  This high temperature high pressure (HTHP) data base consists of literature data for hydrocarbons ranging from methane to C40, and, where gaps in the HTHP regions are were identified, new data collected by our team using a windowed, agitated, variable-volume cell.  The three new models developed in this work, HTHP VT-PR EOS, HTHP VT-SRK EOS, and HTHP PC-SAFT, yield mean absolute percent deviation values (MAPD) for HTHP hydrocarbon density of ~2.0%, ~1.5%, and ~1.0%, respectively. 

An effort was also made to provide accurate hydrocarbon viscosity models based on literature data and data collected with our HTHP, windowed, rolling-ball viscometer.  Viscosity values are estimated with the frictional theory (f-theory) and free volume (FV) theory of viscosity.  MAPD values of ~5% for the viscosity are obtained when the PR and SRK EOSs, or their HTHP VT analogs, are used to estimate the attractive and repulsive pressure input values for the f-theory.  However, the FV theory, which requires fluid density as an input, provides MAPD values of ~3% for the viscosity when coupled with the HTHP VT PR or HTHP VT SRK EOS.  Combined with PC SAFT-based density predictions, the FV theory had MAPD values of less than 2% for hydrocarbon viscosity values.