Density Measurements and Thermodynamic Modeling of Two Crude Oil Samples

The growing worldwide demand for oil and gas is driving the exploration and production industry to search for new resources in deeper formations. As deeper formations are drilled higher temperatures and pressures and are encountered. These high-temperature, high-pressure (HTHP) wells are characterized as exhibiting pressures greater than 69 MPa and temperatures greater than 423 K. Drilling HTHP wells is very capital-intensive and so accurate models for thermodynamic properties, such as density and isothermal compressibility, are essential for accurate assessment of the amount of recoverable petroleum within a reservoir. To our knowledge, there are no crude oil density data in the literature for pressures in excess of 155 MPa. In this work we present density data for two Gulf of Mexico crude oils at pressures to 276 MPa and temperatures to 523 K. Methane gas is also added to each crude oil to simulate a “live” crude oil. A Tait relationship is used to correlate the measured density data; from this relationship a reference value for isothermal compressibility is obtained. PC-SAFT is used to predict the density and isothermal compressibility values for the hydrocarbons that compose the crude oil. A special set of new PC-SAFT parameters are used to obtain accurate predictions of fluid properties in the single -phase region at HTHP conditions. These parameters are determined with a knowledge of the measured aromaticity of the oil in question. Oil density and isothermal compressibility are successfully predicted to within 1-4% and 1-10% of experimental values, respectively.