Miscible/Immiscible carbon dioxide injection is considered to be as one of most effective technology to improve oil recovery from complicated formations, and hard to recover oil reserves, in particular. Application of this technology can increase ultimate oil recovery by 10–15% and even more1. One of the main advantage of this technology is that it can be applied in a wide range of geological conditions for production both light and heavy oils. Striking illustration of this technology high efficiency is the fact that the number of active carbon dioxide (CO2) projects worldwide sharply increased during last 20 years, from 30–35 in the beginning of 1980s to almost 100 in 2000, while oil production increased from 25,000 BPD to more than 200,000 BPD during this period2. One of the main factor restraining wide application of this technology is its dependence on the natural CO2 sources, transportation of CO2, breakthrough of CO2 to production wells, corrosion of well and field equipment, safety and environmental problems etc. Except Hungary reserves of natural CO2 for field application of this technology are not existed in Europe. This restrains wide implementation of CO2 injection not only in many European countries but also worldwide where this technology could be efficiently applied and significantly improve oil production as well as ultimate oil recovery from depleted oil formations. Carbon dioxide enhanced oil recovery may be the key to recovering huge amount of oil from highly watered, depleted, heterogeneous and other type of so called "hard-to-recover" oil reserves. One of the main advantage of proposed technology is eliminating of CO2 negative impact on the environment and strong control of the process. New understanding of the nature of miscible displacement process when behavior of CO2 can be explain as a "super critical fluid" opens a unique future of oil displacement using this technology. Results of R & D as well as new approach in estimation of the efficiency of EOR technology application are described below. Proposed technology of in-situ CO2 generation is based on exothermic chemical reaction between gas forming water solution and low concentrated active acids. Introduction Displacement of oil by CO2 in miscible/immiscible conditions to improve oil recovery allowed to determine the mechanism of oil displacement and possible positive and negative factors affecting on oil displacement process3–6. Among main positive factors affecting on displacement of oil by CO2 the following can be outlined:CO2 solved in water increases water viscosity by 20–30% and its mobility by 2–3 times,CO2 solved in oil reduces oil viscosity by 1.5 - 2.5 times,CO2 solved in oil decreases interfacial tension in oil-water contact,CO2 solved in oil increases oil volume what affects on displacement of residual oil. At the same time following negative factors accompanied displacement of oil by CO2 have been observed:Changing of thermobaric conditions results on reduction of CO2 concentration followed by coagulation and sedimentation of waxes and asphaltens from oil,CO2 breakthrough to oil producers,Well and oil field equipment corrosion,CO2 transportation problems,High cost of technology,Shortage or absence of CO2 sources in the vicinity of oil fields. It is clear that development of technology where displacement agent to displace oil from formation (CO2) is generated in-situ avoiding any surface facility and any negative impact on the environment has a high priority.

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The experimental studies were conducted to estimate the effect of surfactant additives on the volume and the pressure of the CO2 gas generated according to the new proposed technology. An experimental device was designed and built specifically for these purposes. The designed setup allowed initiating and controlling the reaction between the "gas-yielding" (GY) and "gas-forming" (GF) agents proposed by this technology. The temperature was controlled, and the generated gas pressure and volume were recorded during the reaction process. Three types of surfactants were tested to estimate the effect on volume and pressure of generated CO2 gas. The preliminary experimental results on CO2 gas pressure measurements demonstrated that the gas pressure increases withsurfactant addition,decreasing the temperature, andincreasing salinity of the system. INTRODUCTION Dense phase gases (carbon dioxide, nitrogen, light hydrocarbons, etc.) are used to develop miscibility with crude oil in enhanced oil recovery processes. Due to the following reasons, carbon dioxide (CO2) flooding is considered the fastest-growing improved oil recovery method [1]: However, due to the low viscosity of dense CO2 (up to 20% of viscosity of oil), displacement front instabilities and a premature CO2 breakthrough is observed in many cases. In order to control the mobility of CO2 flooding, the gas injection is alternated with surfactant solution [1], which results in generation of foam (colloidal dispersion of gas in liquid). A thin intermediate boundary between the dispersed and continuous phases is called interface. The region that covers the thin film with two interfaces on its each side is called lamella. Each lamella has a link to other lamellae.