This paper presents a complete sets ofexperimental work on finding the optimum miscibility condition for 8 Iranian oil fields. During these experimental works new miscibility criteria for slim-tube apparatus investigated. Then a comprehensive simulation procedure to model the miscibility process in slimrube apparatus is given. In order to investigate the applicability of the empirical correlations. the results of experiments and simulation runs are compared to the prediction of different correlations which show unreliable prediction of the correlations. Finally, a semi-empirical correlation is developed, which can predict the minimum miscibility pressure (MMP) with an acceptable error.


In order to enhance the oil recovery from reservoirs, there are several methods. Hydrocarbon gas injection is one of the most suitable methods for some Iranian reservoirs. If the injected gas becomes miscible with the oil, the residual oil will be decreased, therefore, a high amount of oil will be recovered which is favourable. The miscible displacement of oil by injected gas is only achieved at a pressure higher than a certain minimum pressure. The determination of this minimum miscibility pressure (MMP) is vital to any gas injection process. When a study on miscibility of a crude oil and selected gas is stated, two methods are in principal to get the optimum miscibilty condition: laboratory experiments such as slim-tube dynamic tests, and modelling (theoretical and empirical). A series of experiments with slim-tube miscibility apparatus were done, then a fully compositional simulator were used to model the miscibility process in slim-tube apparatus. The results show that the available gases alone or with some enrichment can develop miscibility process with crude oils at reservoir condition.

The objective of this study is to investigate different methods to obtain the optimum condition of the injected gas to get the maximum recovery.


In Iran, the gas injection was started for some reservoirs. Some other reservoirs are candidates for gas injection in future. However, these gas injection processes are for pressure maintenance or increasing the reservoir pressure purposes1.

For miscible flooding to be a competitive process in a given reservoir, several conditions must be satisfied:

  1. an adequate volume of solvent must be available at a rate and cost that will allow favourable economics,

  2. the reservoir pressure required for miscibility between the solvent and oil in question must be attainable, and

  3. incremental oil' recovery must be sufficiently large and timely for project economics to withstand the added costs.

Hydrocarbon solvents in other countries such as U.S. could be too expensive. However, supply and cost in Iran as well as conservation policies could be favourable for projects with hydrocarbon solvents. Determining the MMP (item 2), is the main object of this paper, which will be discussed in next paragraphs, and economical considerations are (item 3), are vital for any industrial projects.


There are basically two methods to study the miscibility process.

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