Experimental and Theoretical Studies on the Fluid Properties Required for Simulation of Thermal Processes

Abstract

Experimental phase equilibrium data are presented for three reservoir oils at conditions approximating those encountered in in-situ thermal recovery processes. The fluid systems involved consist of three major groups of components: flue gas, water, and crude oil. Data were measured at temperatures from 204.4 to 371.1°C (400 to 700°F) and pressures from 6996.0 to 20785.6 kPa (1,000 to 3,000 psia). Experimental phase equilibrium data were used to develop a correlation of binary interaction coefficients of crude-oil fractions required for the Peng-Robinson equation of state. Phase equilibrium data predicted using the Peng-Robinson equation of state, using our interaction coefficients, are compared with experimental data. Generally, the Peng-Robinson equation of state predictions were in close agreement with the experimental data. Effect of feed gas/oil ratio and water/oil ratio on the equilibrium coefficients was examined through the Peng-Robinson equation of state. A study on the feasibility of representing the crude oil by only two fractions was made also. This study includes a procedure for lumping the crude-oil fractions and examples showing the importance of mixing rules in determining the pseudo critical properties of lumped fractions. Introduction The steady growth of commercial thermal recovery processes1 has created a need for basic data on phase equilibria that involve water and hydrocarbons ranging from methane to high boiling-point fractions. The in-situ thermal recovery processes often are operated at pressures above 6800 kPa (1,000 psia) and temperatures above 200°C (400°F). Experimental data and theoretical correlations on phase equilibria approximating these systems are virtually nonexistent. Early work by White and Brown2 dealt with high boiling-point hydrocarbon phase equilibria. However, the highest pressure studied was 6894.8 kPa (1,000 psia) and the lightest component was pentane. Poettmann and Mayland,3 on the basis of an empirical correlation,4 constructed charts of equilibrium coefficients, or K values, as functions of pressure and temperature for various boiling-point fractions. But the maximum pressure studied was 6894.8 kPa (1,000 psia). Later, Hoffmann et al.5 studied phase behavior of a gas-condensate system with the highest pressure reaching 20 684.3 kPa (3,000 psia) but the highest temperature investigated was only 94.2°C (201°F). In 1963, Grayson and Streed6 reported experimental vapor/liquid equilibrium data for high-temperature and high-pressure hydrocarbon systems. They also extended the Chao-Seader correlation to cover the higher temperature ranges. However, the. major light component in Grayson and Streed's system was hydrogen. Recently, because of the increasing activity in carbon dioxide flooding processes, the phase equilibria of systems involving carbon dioxide and crude oil has received attention. Simon et al.7 studied phase behavior and other properties of carbon-dioxide/reservoir-oil systems. Shelton and Yarborough8 examined phase behavior in porous media during carbon dioxide or rich-gas flooding. No extensive data on equilibrium coefficients were reported in those papers, and the temperature ranges (out of physical reality) were below 93.5°C (200°F). None of these papers surveyed included water as a component.

The Use of Semicontinuous Description To Model the C7+ Fraction in Equation of State Calculations

“…Lee et al 3 proposed plotting all properties available for each fraction with the boiling point as the independent variable. Those fractions with similar slopes were then grouped together.…”

A New Equilibrium Coefficient Correlation Method for Compositional Simulators

“…To examine the deviations of approximiBbng the activity coeffi ci ent, x.;(p) , si mply by y. , lOu 1 we calculate Yi(P) and Yi for three quaternary mixtures, using the Chao-Seader's correlation. The gas-phase fugacity coefficient, 4>i' are nearly equal to unity in the low pressure region, and are, therefore, set to be equal to uni&l in the calculations.…”

“…Cubic equations of state [1][2][3], though convenient and reliable in the calculation of phase equilibrium, suffer slow numerical convergence in performing flash calculations near the critical region and are generally not suitable for multi-dimensional field-scale recovery simulations.…”

Impact of fluid characterization on compositional gradient in a volatile oil reservoir

“…After distributing the plus fraction, properties for each SCN are estimated by empirical correlations and at the end, synthetic distribution is lumped into a smaller number of hypothetical components. Whitson mentions that number of components used to describe a reservoir fluid depends mainly on the process being simulated (Whitson and Brulé 2000) and this is the main reason for variety of grouping schemes presented in numerous publications (Whitson and Brulé 2000;Lee et al 1979;Behrens and Sandler 1986).…”