Determination and Prediction of CO2 Minimum Miscibility Pressures (includes associated paper 8876 )
- W.F. Yellig (Amoco Production Co.) | R.S. Metcalfe (Amoco Production Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- January 1980
- Document Type
- Journal Paper
- 160 - 168
- 1980. Society of Petroleum Engineers
- 4.3.4 Scale, 4.1.5 Processing Equipment, 2.4.3 Sand/Solids Control, 4.6 Natural Gas, 5.3.2 Multiphase Flow, 5.2 Reservoir Fluid Dynamics, 4.3.3 Aspaltenes, 4.1.2 Separation and Treating, 5.4 Enhanced Recovery, 5.2.1 Phase Behavior and PVT Measurements, 5.4.2 Gas Injection Methods, 5.4.9 Miscible Methods
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An experimental procedure is presented for determining the CO2 minimum miscibility pressure for a reservoir oil. The procedure consists of performing CO2 displacements at various pressure levels in a sand-packed slim tube. A correlation is presented for predicting reservoir oil CO2 minimum miscibility pressures based on reservoir temperature and bubble-point pressure.
The injection of carbon dioxide (CO2) for secondary and tertiary oil recovery has received considerable attention in the industry because of its high displacement efficiency and relatively low cost. Miscible recovery of a reservoir oil can be achieved by CO2 displacement at a pressure level greater than a certain minimum. This minimum pressure is hereafter defined as the CO2 minimum miscibility pressure (MMP). The CO2 MMP is an important parameter for screening and selecting reservoirs for CO2 injection projects. For the highest recovery, a candidate reservoir must be capable of withstanding an average reservoir pressure greater than the CO2 MMP. A knowledge of the CO2 MMP is also important when selecting a model to predict or simulate reservoir performance as a result Of CO2 injection. Methods of predicting CO2 MMP's based on reservoir composition and reservoir temperature have been presented in the literature. These methods have limitations that can result in large discrepancies when compared with experimentally determined values. In addition, there is no generally accepted standard method in the literature for experimentally determining the CO2 MMP for an oil. An experimental study was undertaken to obtain a better understanding of the effects of temperature and oil composition on the CO2 MMP determined for an oil. CO2 MMP's were determined using the sand-packed coil (or slim-tube)method. Results of this study were used to develop a correlation for predicting the CO2 MMP for an oil. The purpose of this paper is to present the correlation for predicting CO2 MMP's that was developed from this study. Another purpose is to propose that the sand-packed coil method be used as a standard method of experimentally determining the CO2 MMP for an oil.
Experimental Study Experimental Variables
Two variables were considered in this study: oil composition and temperature. Oils were considered to consist of three fractions: a light fraction consisting primarily of C1 and small amounts of N2 and CO2; an intermediate fraction consisting of hydrocarbons with molecular weights between C2 and C6; and a heavy fraction (C7+) consisting of hydrocarbons with molecular weights equal to or greater than normal C7. The oils discussed in this paper were prepared by combining the molar amounts of these fractions in varying proportions. In general, the same C7+ , fraction was recombined with different amounts of the light (C1 + CO2 + N2) and intermediate (C2 - C6) fractions. With the exception of one oil, the same ratio of one component to another within each fraction was maintained regardless of the total amount of the fraction in any oil. The C7 + fraction was prepared by batch distilling a west Texas 30 degrees API (0.87-g/cm ) separator oil. This distillation had approximately five theoretical plates and was performed at atmospheric pressure and 208 degrees F (98 degrees C).
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