Parachors Based on Modern Physics and Their Uses in IFT Prediction of Reservoir Fluids
- D.S. Schechter (New Mexico Petroleum Recovery Research Center) | B. Guo (New Mexico Petroleum Recovery Research Center)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- June 1998
- Document Type
- Journal Paper
- 207 - 217
- 1998. Society of Petroleum Engineers
- 5.8.6 Naturally Fractured Reservoir, 4.1.2 Separation and Treating, 4.3.4 Scale, 4.6 Natural Gas, 5.2 Reservoir Fluid Dynamics, 4.1.5 Processing Equipment, 5.4.2 Gas Injection Methods, 5.5 Reservoir Simulation, 5.2.1 Phase Behavior and PVT Measurements
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Prediction of interfacial tension (IFT) is essential for modeling many secondary and tertiary oil recovery processes. The parachor method has been widely used to predict IFT. There has been considerable confusion in the literature concerning the parachor method for estimating IFT. The confusion is primarily based upon the lack of clarity concerning the scaling exponent and parachors derived based on this exponent.
According to modern physics, the theoretical value of the scaling exponent is 3.88 for all pure substances, although several values may be found in the literature, usually altered to match existing data. This paper addresses: (1) clarification of the confusion about the scaling exponent, (2) derivation of parachors for pure species occurring in petroleum fluids and oil cuts, and (3) verification of the validity of these derived parachors in IFT prediction of reservoir fluids.
We have analyzed experimental data for various compounds and compound mixtures occurring in the petroleum fluids and found that the 3.88 is the unique scaling exponent for pure species inside and outside, to some large extension, of the critical region. Taking 3.88 as a fixed scaling exponent, parachors of 139 crude oil components are back-calculated using surface tension and density data obtained from experiments by previous investigators. These parachors are compared with three selected parachor correlations for IFT predictions of six available crude oil and CO2 mixtures, and found to be more accurate.
Interfacial tension (IFT) is one of the key parameters controlling oil recovery from oil reservoirs. In low IFT region that occurs around the critical point close to dew and bubble point lines the IFT dominates relative permeabilities and residual liquid saturations. Prediction of IFT is essential for modeling many secondary and tertiary oil recovery processes. However, there is no consistent standard by which this may be accomplished.
Prediction of IFT of multicomponent systems using thermodynamics of adsorption at the interface has been demonstrated by Guggenheim and Adam at low pressures where the vapor density is negligibly small. The commonly used methods in petroleum industry for predicting the IFT are empirical correlations called Parachor Methods because of their simplicity. Although recently the gradient theory has been demonstrated to be in general superior in comparison to the parachor method, it may be applied accurately to interfaces at only conditions far from the critical region according to Cornelisse et al. We are interested in calculations of IFT of reservoir fluids, both in the low and high IFT regions. Therefore, only Parachor Methods are discussed in this paper.
Based on experimental observations, Macleod recognized the following relation between surface tension and densities:
(1) where is surface tension, and are densities of the liquid and vapor phases, respectively, and C is a constant. The exponent 4 was adopted from Van der Waal's equation which is based on the assumption that the force of attraction between molecules falls off as the 4th power of distance between them. Sugden related the constant C to chemical composition of the substance. He defined a parameter by
(2) where M is molecular weight and P is called parachor which was believed to be a measure of the molecular volume and chemical composition.
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