Abstract

Carbon dioxide (CO2) flooding is an efficacious method of enhanced oil recovery (EOR) that has nowadays become one of the most important EOR processes. It is a very complicated process, involving phase behavior that could increase oil recovery by means of swelling, evaporating and lowering oil viscosity. The present investigation reports the results of extensive experimental and theoretical work (with the aim of computer software, ECLIPSETM) to determine the viscosity and swelling factor changes of the live oil in the Cheshmeh Khoshk reservoir at southern of Iran (Ilam District) and also minimum miscible pressure. In this study we setup a series of slim tube experiments. In order to get representative fluid samples of areservoir, it was necessary that the right operation of mixing the separator oil and gas samples to match the bubble point pressure be carried out. And, the potential application of the study is that we could have a good estimate of the recovery improvement under CO2gas injection, which will be the basic input parameters for the economic feasibility study and also a decision can then be made whether to implement or abandon the prospective project.

Introduction

Carbon dioxide gas as an injection fluid into oil reservoirs has been a recognized well and tested as Enhanced Oil Recovery (EOR) method, because CO2dissolves easily into oil, it reduces oil viscosity, and it can extract the light components in oil at sufficiently high pressure, and it can become miscible with oil at very low pressure [1]. The injection of carbon dioxide for secondary and tertiary oil recovery has received considerable attention in the industry because of its high displacement efficiency and relatively low cost [2].

It appeared in 1930's and had a great development in 1970's. Over 30 years' production practice, CO2flooding has become the leading enhanced oil recovery technique for light and medium oil. It can prolong the production lives of light or medium oil fields nearing depletion under waterflooding by 15 to 20 years, and may recover 15% to 25% of the original oil in place [3]. Experience gained from CO2flooding worldwide indicates that enhanced oil recovery by using CO2as injection gas may result in additional oil ranging from 7 to 15 % of the oil initially in place [4].

CO2flooding process involves very complicated phase behavior, which depends on the temperature, pressure and fluids properties of a certain reservoir. Many factors have been found contributing to the oil recovery in CO2flooding. These mainly include: Low interface tensions, Viscosity reduction, Oil swelling, Formation permeability improvement, Solution gas flooding, and Density change of oil and water [3].

In the case of viscosity, there is a reduction for carbon dioxide as long as temperature increases. Appreciable solubility of carbon dioxide in the crude oil reduces its viscosity. At low temperatures, viscosity reduction for light oils is more than heavy oils [5].

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