Prediction of Miscibility for the Enriched-Gas Drive Process

Abstract

Minimum miscibility pressure (MMP) is an important parameter for screening and selecting reservoirs for miscible gas injection projects. This paper presents a new correlation for the enriched-gas process that can be used to calculate the miscible slug compositions which consist of methane and mixtures of intermediate molecular weight hydrocarbons such as ethane to butane. The miscibility correlation was developed from MMP predictions of four reservoir fluids and several enriched-gas mixtures using the Peng-Robinson equation-of-state model. The correlation can be used to predict MMP for a fixed slug composition, or predict methane concentration for a given operating pressure. The correlation was tested with published data and showed an average prediction error of ± 2.5 mol% methane. The miscibility conditions for two reservoirs and several enriched-gas mixtures were also determined in this study using slim tube apparatus. The miscibility in the slim tube tests was judged from the change of phases in the miscible transition zone rather than arbitrarily choosing oil recovery at the 90% level. A photosensor was used to aid the determination of miscibility. This experimental technique has proved to be very consistent. The results of these tests were compared with the new correlation and showed an average prediction error on MMP of less than ± 4%. In general, either a higher pressure or a higher concentration of C2 to C4 hydrocarbons in the injection gas is required for achieving miscibility as (1) reservoir fluid C5+ molecular weight increases, (2) average molecular weight of C2 to C4 components in the injection gas decreases, or (3) reservoir temperature increases.

A rigorous approach to predict nitrogen-crude oil minimum miscibility pressure of pure and nitrogen mixtures

“…More than 90 experimental data sets were provided from variety of literature sources including Firoozabadi and Khalid [20], Glaso [16], Hudgins et al [17], Sebastian and Lawrence [19], Hanssen [31], Kuo [32], Al-Ajmi et al [33], Jaubert et al [34], and Husodo et al [35]. Table 1 shows the range of data used in this study.…”

Improved Method for Calculating Minimum Miscibility Pressure for Gas Flooding

“…We know of several empirical equations for calculating the MMP for oil and hydrocarbon gas [8][9][10][11]. The most accurate and widely used equations were developed by Kuo (1985), Firoozabadi and Aziz (1986), and Pedrood (1995).…”

“…The most accurate and widely used equations were developed by Kuo (1985), Firoozabadi and Aziz (1986), and Pedrood (1995). Table 2 gives the indicated equations and the restrictions on their application.…”

“…The optimization function contains 12 decision variables (m = (m 1 , m 2 , m 3 ... m 12 )). We used literature data [8][9][10]13,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] to construct a database for the MMP of gases and oils. The database includes data from 97 MMP measurements in the temperature range 38°C-130°C and average molecular weight of the C 7+ fraction ranging from 144 to 302 g/mol.…”

“…The MMP can be found experimentally [3][4][5][6][7] and by calculation using empirical equations [8][9][10][11] and the equation of state [12,13]. The primary experimental method for estimating the MMP is the slim-tube test [3].…”