The Effects of Light Ends and High Pressure on Paraffin Formation

Abstract

A thermodynamic model for paraffin formation is presented which accurately accounts for the effects of light ends, such as methane, ethane, and propane, and high pressures. The model uses the Simplified, Perturbed Hard Chain equation of state for all fluid phase fugacities and contains no adjustable parameters for the solid-liquid equilibria. Model predictions are compared to binary solid-liquid, solid-vapor, and solid-liquid-vapor equilibria data with good results. Also, a high-pressure, coldstage microscope technique was developed to measure cloud points of live oils with which to test the model. Comparisons between the predicted and measured cloud points for live oils are presented.

Evaluation of Wax Deposition and Its Control During Production of Alaska North Slope Oils

“…STO WAT gives higher value than live oil WAT of the same crude oil. This is to be expected, as light ends increase the solubility of paraffin molecules (Huanquan et al, 1997), while increase in pressure depresses the WAT below the bubblepoint pressure (Brown et al, 1994). The entire wax deposition process is complex.…”

“…Here wax appearance temperature decreases with increase in pressure up to bubblepoint pressure (Brown et al, 1994) due to dissolution of light ends back into the liquid phase. The WAT increases with increase in pressure for STO, commonly referred to as dead oil (Brown et al, 1994;Karan et al, 2000). Huanquan et al (1997) reported that the WAT increases with increase in pressure for a fixed component liquid mixture.…”

“…Hence, the solubility of wax is reduced with the loss of these light ends. Brown et al (1994) studied the effect of pressure on the cloud point of dead oil as well as live oil by measuring cloud point at atmospheric pressure and higher pressures. The wax appearance temperature increases with increase in pressure above the bubblepoint, at constant composition.…”

Green River Formation Water Flood Demonstration Project. Annual report, April 1, 1994--March 31, 1995

“…There has been a great deal of work on the thermodynamic models for predicting paraffin (or wax) precipitakion from oils (Weingarten and Euchner, 1988;Won, 1985,19SG,19S9;Hansen, 1988;Pedersen, 1991;Brown, 1994). Ring and Wattenbarger (1992) developed a computer simulator for predicting oil recovery in paraffinic crude reservoirs.…”

“…The calculations illustrate that reasonable predictions could be obtained by using the simplest of the Won's models (neglecting the effect of activity coefficients) with heats of fusion modification proposed by Pedersen et a1 (Pedersen, Skovborg and Ronningsen, 1991). Won's most recent model (1989) and some of the more recent models (Brown, et al, 1994) were not compared in this study.…”