Asphaltene and wax depositions in the course of production of many Iranian reservoirs have become a serious problem. In order to investigate the effects of injecting rich and dry gases and also nitrogen, on the asphaltene precipitation process, a comprehensive research study was launched.
The three phase equilibrium calculation of NGHIEM and his colleagues was used . In the method pure asphaltene in the oil was considered as solid and the heavy part of the oil was split as precipitating and non-precipitating. The provided model was able to describe the phase behavior of reservoir oil encountered with a compositional disturbance caused by injecting light fluids into the reservoir during the production period.
In this work, first, the natural depletion model of each case was constructed and then the changes of behavior by injecting rich and dry natural gases and also high nitrogen content gas were investigated. Also the changes in the onset of asphaltene precipitation for different injections were shown. The achieved results showed that the nitrogen gas had more moderate effect on precipitation process compared to more vigorous effect of dry and rich gases.
The nature of asphaltene and its role in the production and processing of crude oils has been the topic of numerous studies. This is due to the fact that the economics of oil production can be seriously affected by the asphaltene deposition problems.
The precipitation of asphaltene aggregates can cause such severe problems as reservoir plugging and wettability reversal. The adsorption of asphaltene aggregates at oil-water interfaces has been shown to cause the steric stabilization of (W/O) petroleum emulsions. Consequently, the oil industry is in critical need of quantitative tools and thermodynamic data to predict asphaltene solubility and aggregation as a function of crude oil composition and reservoir temperature and pressure. In general asphaltene both decreases the conventional oil production by deposition and also causes a higher percent of oil to remain underground.
Asphaltenes are more likely found in heavy oil reservoirs in which there are more heavy components and therefore there is a higher risk of Asphaltene deposition. However, the weight percent of asphaltene does not indicate the existence of a problem situation. There have been cases in which in spite of their low asphaltene content a serious deposition problem was encountered.