Chemical methods of enhanced oil recovery (EOR) efficiency is associated with improved displacement of oil with original or slightly altered properties from unswept reservoir zones, and better displacement of mobile residual oil with high content of resin and asphaltene components from flushed zones. Studies on the effects of various production stimulation technologies remain important. The results of field-scale research provide the most valuable data necessary for feasibility studies and development of innovative technologies as well as for improvement of existing improved (IOR) and enhanced oil recovery methods.
The paper presents the results of comparative analysis of the composition and properties of crude oil samples collected before and after stimulation with the aim to improve sweep efficiency and oil recovery. To analyze oil composition, a number of physical and chemical methods were used including thermoanalysis, gas-liquid chromatography, gas-solid chromatography, infrared spectroscopy. It has been found that stimulation treatments promote oil displacement from unswept reservoir intervals containing oil with original or slightly altered properties. Injection of alkaline-polymer systems resulted in reduction of oil viscosity and asphaltene content while the content of middle distillates and light hydrocarbons increased. Similar changes were observed after application of integrated stimulation technology that consists in gel treatments followed by acid injection.
The results suggest that the applied technologies improve oil displacement from reservoir intervals and zones containing low-viscosity oil. These findings have been confirmed by well logging data. Chemical floods result in decrease of asphaltene content, increase of middle distillates and light hydrocarbons in produced oil, and overall mobilization of residual oil. Monitoring of composition and properties of produced oil makes it possible to understand the mechanisms of chemical EOR and confirms efficiency of chemical flooding.
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