Swelling/Extraction Test of a Small Sample Size for Phase Behavior Study

Abstract

Swelling/extraction tests are single-contact phase-behavior experiments to measure the solubility of CO 2 dissolved in crude oil and the amount of hydrocarbon that CO 2 can extract or vaporize from crude oil. The tests are commonly conducted in a visual PVT cell with a large sample size (40-100cc). In this paper, an easy operated apparatus capable of determining phase behavior with a significantly smaller sample size (3 to 14 cc) is described. The apparatus consists of a high-pressure view cell, high-pressure and precision syringe pump filled with CO 2 , a water bath, and accessories to measure the temperature and pressure. The device is capable of determining vapor-liquid, liquid-liquid and vapor-liquid-liquid equilibrium commonly observed in a high pressure CO 2 enhanced oil recovery process. The solubility of CO 2 in oil, the expansion volume of oil due to the dissolution of CO 2 as well as the phase transition during the test were quantified with excellent reproducibility. The molar volume of oil saturated with CO 2 correlated linearly with the mole fraction of dissolved CO 2 suggesting ideal mixing in the liquid phase. The phase behavior between CO 2 and crude oil samples with different composition, temperature and pressure is discussed.

An improved method for estimating minimum miscibility pressure through condensation–extraction process under swelling tests

“…First, it reduces the uncertainties on the resulting MMP under swelling tests as noted by Harmon and Grigg (1988). Second, it improves the evaluation technique proposed by Tsau et al (2010).…”

“…However, the miscibility should occur before the minimum value of the swelling factor is reached as noted by Tsau et al (2010). In this regard, Harmon and Grigg (1988) studied further the case by constructing a swelling factor curve as a function of pressure and compared it with the results of a slim tube experiment.…”

“…The MMP has also been observed under swelling tests by Tsau et al (2010). Based on their laboratory work, they proposed to estimate the MMP using a plot of swelling factor vs. pressure.…”

“…Through this paper, we propose a method of analysis to improve the method previously presented by Wang (1986), Harmon and Grigg (1988), and Tsau et al (2010) to estimate the MMP. The proposed method is composed of 3 (three) parts:…”

“…First, we construct a plot of the swelling factor vs. pressure as it was suggested by Tsau et al (2010). In the same graph, we also construct the oil recovery as a function of pressure resulted from a slim tube experiment similar to that proposed by Harmon and Grigg (1988).…”