| Popis: |
Abstract In the frame of the laboratory studies the effect of natural and recycled CO2 and different air/CO2 mixtures on chemical composition of crude oil and gas phase, the rheological and interfacial properties, the flow mechanism and the safety measures were analyzed. The tests were performed at reservoir conditions using formation rock, oil and gas samples. The oxygen content of the gas phase and the gas/oil ratio varied between wide limits. Both crude and asphaltene-free oil were used to determine the consequences of the low temperature oxidation. The main observation of the laboratory studies is that detrimental phenomena using natural and recycled CO2 as a cap gas may not ensue even at long term contact of oil and gas. On the other hand it was also found that the oxygen content of cap gas had completely consumed by the chemical reactions (oxidation, condensation and water formation), and as a result nearly 9 % excess asphaltene formation was observed in both the crude and the asphaltene-free oils. The substantial increase in asphaltene content and the presence of colloidal water resulted in a measurable change in rheological and interfacial properties. Despite these factors the flow and displacement mechanism is ouly slightly influences if the reservoir is of fractured character and the oil is already highly oxidized or is still in prematured evolution state. As a final statement it was concluded that application of natural and recycled CO2 is a reasonable reservoir engineering and technological concept at the Nagylegyel field. However, in certain cases the chemical reactions can be in-situ regulated without jeopardizing the recovery efficiency by re placing the CO2 or inert gases with oxygen-containing cap gas. In this way the application of the artificial gas cap concept may open new vistas in EOR operations in karstic and fractured reservoirs bearing medium or heavy crude oils even in those cases when natural CO2 or CH source is not locally available. P. 183 |
