The gas lift method is an artificial lift method of well production using the energy of compressed gas injected into the well to lift the reservoir fluid to the surface. The formation of paraffin deposits has remained one of the critical oil production problems due to the growing percentage of hard-to-recover reserves in the overall structure. This complication is also typical for many oil and gas fields in Vietnam, such as the White Tiger, White Bear, and Dragon fields. Wax deposit formation negatively affects the operation of individual production wells and the development of the field as a whole, which leads to a decrease in productivity and the need to take measures to remove paraffin deposits, subsequently increasing the downtime period of the well. In order to ensure stable production of highly paraffinic oil, it is necessary to take measures to dewax wells systematically. The frequency of wax removal operations depends on the intensity of the wax formation, which is determined by various technological, technical, and geological factors. The interval between dewaxing operations is called the dewaxing interval period (DIP). This value is an important technological parameter and characterizes the efficiency of a well’s operation. In this study, a comprehensive method has been developed to determine the dewaxing interval period (treatment interval) for gas-lift wells when the formation of wax deposits has occurred. The optimal dewaxing interval period is suggested to be determined by the change in the liquid well flow rate at the point when it falls by 20% from the initial value. In addition, a mathematical model of the time-dependent wax thickness, taking into account the heat and mass transfer laws and the laboratory results using the Cold Finger method, has also been developed. The proposed model for determining the dewaxing interval period was applied to an oil well in Vietnam. The DIP prediction model gave a similar value to the actual DIP field data (6.67 and 6 days, respectively). The obtained results showed that the model had proven its accuracy following the results of a comparison with the field's data of dewaxing operations.

This paper presents the results of the controlled sedimentation process for deasphalting, caused by targeted formation of the fuel dispersed system components incompatibility (proportion of the paraffins with normal structure increase) experimental investigations. The main purpose was to decrease the contained amount of sulphur in sedentary marine fuel and procure VLSFO. Developed and given account of the laboratorial method of instituting the sediment which modifies standard TSP and allows to control the deasphalting with the take-off of sediment and deasphaltisate for future analysis. In this case, 5 components of marine fuels, their basic physical and chemical properties, and chemical group composition were used as an object of study. Based on the data obtained and via use of worked out software package, 6 compositions of marine fuels were specified. Furthermore, they were then produced and their quality attributes were defined. The results show that the deasphalting caused by the components targeted incompatibility is accompanied by the desulphurization. Sulphur concentration took place in the sediment where its content was 4.5 times higher than in composite fuel. At the same time, sediment content fell from 0.9% to 1.02% by weight according to the fuel composition. The sulphur content in the resulting deasphaltisate declined by approximately 15% in relation to original fuel mix, moreover, other quality indicators improved. In order to find out whether the usage of sediment obtained is possible, its composition and structure were assessed. The results of the interpretation showed, that sediments were inclined to bitumens, which allows them to be mixed with sediments as a way to cut process waste. Targeted deasphalting makes it possible for the expenses on reducing sulphur containment in marine residual fuels to be decreased, which expands the opportunities of fuels application according to ISO 8217:2017.